Key Concept: Types of Current

b) Alternating Current (AC)
[Solution Description]
The syllabus states that electricity from power plants to wall sockets is Alternating Current (AC), which can run larger appliances.

Key Concept: Safety Precautions

b) Body conducts electricity better when wet, increasing shock risk
[Solution Description]
Our body is a conductor of electricity, and handling switches with wet hands increases the risk of electric shock, which can cause severe injury or death as mentioned in the syllabus.

Key Concept: Hydroelectric power generation, Energy conversion

c) 2.81 GW
[Solution Description]
First calculate potential energy per second: P.E. = mgh, where m is mass flow rate.
Mass flow rate = density × volume flow rate = 1000 kg/m$^3$ × 1500 m$^3$/s = 1,500,000 kg/s
Potential energy/s = mgh = 1,500,000 × 9.8 × 225 = 3,307,500,000 J/s or Watts
Electrical power output = Input power × efficiency = 3,307,500,000 × 0.85 = 2,811,375,000 W ≈ 2.81 GW

Key Concept: Turbine Functionality

d) Francis turbine
[Solution Description] Large dams like the Bhakra Nangal generally use Francis turbines due to their efficiency and ability to handle a wide range of heads and flow rates. This makes them suitable for large-scale power generation projects.

Key Concept: Transportation, Communication

c) Efficient battery management system supporting GPS
[Solution Description]
For a successful operation, maintaining continuous connectivity and ensuring efficient energy use are crucial. An effective strategy involves incorporating a robust battery management system (BMS) that not only powers the scooter's movement but also supports its communication module. The BMS should prioritize battery life extension and efficient power distribution between the motor and GPS unit to enhance reliability and performance.

Key Concept: Transportation

c) Electric Train
[Solution Description] Electric trains are a common mode of public transport in many urban areas. They run on tracks and are powered by electricity, offering an efficient way to commute across cities.

Key Concept: Importance of warning signs

c) To provide warnings about potential electrical hazards.
[Solution Description]
Danger signs serve to alert people about the potential hazards associated with electricity. They warn individuals that coming into contact with certain parts of electric poles or appliances can be dangerous, helping to prevent accidental injuries or fatalities.

Key Concept: Danger Signs

a) They signal high voltage areas
[Solution Description] Danger signs on electric poles serve as warnings that electricity can be hazardous if not handled properly. These signs are meant to alert people to the potential dangers present and to encourage safe practices around electrical equipment to prevent accidents.

Key Concept: Unit Conversion

c) 2 minutes
[Solution Description]
There are 60 seconds in a minute.
Step 1: Divide the total seconds by 60:
$\text{Minutes} = \frac{120}{60} = 2 \text{ minutes}$

Key Concept: Basic Circuit Components

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that a cell supplies energy for charge movement, which is true. The reason explains the underlying mechanism (chemical to electrical conversion), correctly justifying the assertion.

Key Concept: Battery Configuration

c) The circuit remains open
[Solution Description] If the cells are inserted with incorrect polarity, meaning the positive end of one cell is not connected to the negative end of the other, the circuit is incomplete. Without a complete circuit, electrical current cannot flow through the lamp, which prevents the lamp from glowing.

Key Concept: Incandescent Lamp Structure

c) The filament
[Solution Description] An incandescent lamp produces light due to the filament inside it. When electricity passes through the filament, it heats up and glows brightly, thus emitting light. The filament is typically made of tungsten because of its ability to withstand high temperatures without melting quickly.

Key Concept: Electric lamp, Electric cell, Battery

b) The bulb remains off
[Solution Description] When the cells are connected correctly, with the positive terminal of one cell connecting to the negative terminal of the other, it creates a complete circuit allowing current to flow through and power the bulb. However, if one cell is reversed, the positive terminal is connected to the positive terminal of the next cell, and similarly for the negative terminals. This results in a net voltage difference of zero across the bulb because the voltages cancel each other out. Therefore, no electric current flows through the circuit, and the bulb does not glow. Hence, when one cell is reversed, the lamp will not light up.

Key Concept: Electric cell, Battery, Electric lamp

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
An incandescent lamp works based on the principle of heating effect of electric current. When the switch is turned on, the circuit is completed, allowing current to flow from the battery through the filament. The filament is made of a material with high resistance, such as tungsten. According to Joule's law, the power dissipated as heat in the filament is given by $P = I^2 R$, where $I$ is the current and $R$ is the resistance. The high resistance of the filament causes it to heat up to a temperature where it emits visible light, thus glowing. Therefore, both the Assertion and Reason are correct, and the Reason correctly explains why the Assertion occurs.

Key Concept: Switch Functionality

c) It allows or stops the flow of current in the circuit
[Solution Description] A switch serves as a controlling device in an electric circuit. When the switch is closed (ON), it completes the circuit by allowing current to flow through it. When open (OFF), it breaks the circuit, preventing any current from flowing. This ability to complete or break the circuit makes it possible to control devices like lamps in a simple manner.

Key Concept: Switch Operation

b) The circuit closes, allowing current to flow
[Solution Description] When the switch is turned to the 'ON' position, it closes the circuit. Closing the circuit means that there is a complete path for electrical current to flow from the battery through the lamp and back to the battery. This allows the current to pass through the filament of the bulb, making it glow.

Key Concept: Incandescent lamp

b) The filament inside
[Solution Description] The filament, which is a thin wire fixed in the middle of the glass bulb of the lamp, glows when the torch is switched on. It heats up due to electricity flowing through it, producing light.

Key Concept: Battery Configuration in Torch

b) Positive terminal of one cell to the negative terminal of the next.
[Solution Description] When forming a battery with two cells in a torch, the cells should be arranged such that the positive terminal of one cell is connected to the negative terminal of the next cell. This arrangement creates a series connection, which allows the voltages of the individual cells to add up and power the torch's lamp effectively.

Key Concept: Electric Cell Terminals

a) The metal cap is the positive terminal, and the metal disc is the negative terminal.
[Solution Description] An electric cell has two terminals: a positive terminal and a negative terminal. The metal cap serves as the positive terminal, while the metal disc functions as the negative terminal.

Key Concept: Electric Cell and Battery

b) 4.5V
[Solution Description]
When connecting cells in series, the total voltage is the sum of the individual voltages. Each cell provides 1.5V. Therefore, for three cells:
Total Voltage = $1.5\, \text{V} + 1.5\, \text{V} + 1.5\, \text{V} = 4.5\, \text{V}$
Hence, the total voltage across the series combination of three cells is 4.5V.

Key Concept: Electric Cell Terminal Identification

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
According to the syllabus, an electric cell has two terminals: a positive terminal (metal cap) and a negative terminal (flat metal disc). The assertion correctly identifies the metal cap as the positive terminal, which aligns with the information provided in the syllabus. The reason also correctly states that all electric cells have two terminals, a positive and a negative one, which explains why the metal cap is indeed the positive terminal. Therefore, both the assertion and reason are true, and the reason correctly explains the assertion.

Key Concept: Electric Cell Terminals

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that the metal cap is the positive terminal and the flat disc is the negative terminal of an electric cell. This is correct as per the syllabus description. The reason explains that in a torch, connecting the positive terminal of one cell to the negative terminal of another ensures the proper flow of current, making the lamp glow. Both statements are true, and the reason correctly explains the assertion since the correct connection of terminals is essential for the circuit to work.

Key Concept: Structure of an electric cell, Positive and negative terminals, Series Connection of cells

Correct answer option (either of a), b), c) or d)) Negative terminal
[Solution Description]
The battery is formed by connecting multiple cells in series such that the positive terminal of one cell is connected to the negative terminal of the next. This creates a path for current flow from the first cell through to the last cell. If we consider three cells connected in series, the positive terminal of the first cell should be connected to the negative terminal of the second cell. The negative terminal of a cell is typically indicated by a flat metal disc. The concept ensures current flows efficiently through the series arrangement.

Key Concept: Electric Cell Terminal Identification

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
According to the syllabus, an electric cell has two terminals: a positive terminal marked with a (+) sign (metal cap) and a negative terminal marked with a (–) sign (flat metal disc). The assertion correctly states that the metal cap is the positive terminal, which aligns with the syllabus. The reason also correctly describes the marking convention for terminals. Moreover, the reason logically explains why the metal cap is identified as the positive terminal (because it bears the (+) mark). Therefore, both the assertion and reason are true, and the reason correctly explains the assertion.

Key Concept: Connecting an LED to a battery

a) The LED's longer wire is connected to the negative terminal of the battery
[Solution Description] For an LED to light up, its longer wire (positive terminal) should connect to the positive terminal of the battery, while the shorter wire (negative terminal) should connect to the negative terminal. If these wires are connected incorrectly, the LED will not glow due to reverse polarity.

Key Concept: LED Connection

c) Longer wire to positive terminal
[Solution Description] An LED will illuminate when its longer lead (positive terminal) is connected to the positive terminal of the battery, and the shorter lead (negative terminal) is connected to the negative terminal of the battery. This ensures proper current flow through the diode.

Key Concept: Energy Supply Duration and Voltage

c) Increases both voltage and duration
[Solution Description] Using multiple cells in series increases the voltage available in the circuit because the voltages of individual cells add up. This increased voltage can provide more energy per unit time. Additionally, with more cells, energy can be supplied over a longer period because the cumulative capacity of the cells is greater than a single cell alone. This ensures that devices like torches can operate for extended periods without needing frequent replacements.

Key Concept: Battery Connection Order

a) Positive to Negative
[Solution Description] To ensure that the lamp glows, we need the current to flow through the circuit. For this reason, the positive terminal of one cell should connect to the negative terminal of the next cell. This series connection allows the voltage from each cell to add up, providing enough energy for the lamp. Connecting cells in any other configuration would prevent the proper flow of electricity, thus stopping the lamp from glowing.

Key Concept: Cell Orientation in Holder

b) Towards the spring side of the holder
[Solution Description] According to the correct placement described in the syllabus, each cell's negative terminal should be towards the spring side of the holder. This orientation will allow the battery to function correctly by completing the circuit.

Key Concept: Identifying battery terminals

b) The terminal connected to the positive of the first cell
[Solution Description] In a typical cell holder where cells are placed side by side, the positive terminal of the battery is connected to the positive terminal of one cell, and the negative terminal is connected to the negative terminal of the other cell. To determine the positive terminal of the battery, check which terminal is directly connected to the positive terminal of one of the cells via the metal strip or wire.

Key Concept: Positive and negative terminals of an electric cell

a) It is the positive terminal
[Solution Description] The metal cap on an electric cell serves as the positive terminal. In contrast, the flat metal disc at the opposite end is typically the negative terminal. This identification helps in correctly placing cells in devices to form a complete circuit.

Key Concept: Electric Cell, Battery, Circuit Diagram

a) 3.0 V
[Solution Description] In a series connection, the voltages of individual cells add up. Here, two cells are connected in series, so the total voltage provided by the battery is $V_{\text{total}} = 1.5\, \text{V} + 1.5\, \text{V} = 3.0\, \text{V}$. Since the LED and the lamp are connected in parallel, they both experience the same voltage supplied by the battery. Therefore, the voltage across the LED is 3.0 V.

Key Concept: Incandescent Lamp

d) The filament
[Solution Description]
Inside an incandescent lamp, the thin wire known as the filament heats up when electricity passes through it. This heating causes the filament to glow and produce light.

Key Concept: Electric cell, Battery

c) The torch will not turn on due to incorrect current path formation.
[Solution Description] In a correct configuration for a battery in a series circuit, the positive terminal of one cell connects to the negative terminal of the next cell. This arrangement allows current to flow through the entire setup. However, if both cells are placed with their positive terminals facing the same direction, there will be no path for the current to complete the circuit as required. The flow of electric charges will stop at the point where the two similar terminals meet, preventing current flow entirely. Thus, the lamp will not glow.

Key Concept: Complete Circuit Condition

a) Because of a broken filament
[Solution Description] An incandescent lamp may not glow if its filament is broken. A broken filament stops the flow of current within the circuit, preventing the lamp from completing the circuit necessary for the current to pass through and make it glow. This condition is often referred to as the lamp being 'fused.'

Key Concept: Electric Circuit

c) A complete circuit
[Solution Description] For an electric lamp to glow, a complete path must be provided for the electric current to flow through it. This means connecting one terminal of the lamp to one terminal of the electric cell and the other terminal of the lamp to the other terminal of the cell using wires. This complete setup forms an electrical circuit, allowing current to pass through the filament of the lamp and making it glow.

Key Concept: Incandescent Lamp and Electrical Circuit

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that an incandescent lamp glows when connected to a cell because the filament gets hot and produces light. This is true as per the syllabus where it mentions that the filament glows when current passes through it. The reason states that the filament is connected to two terminals allowing current to flow, heating it up. This is also correct and explains why the assertion happens. Thus, both are true, and the reason correctly explains the assertion.

Key Concept: Properties of Electric Current in a Circuit

c) The lamp will glow normally without any effect.
[Solution Description] In a simple electric circuit with an incandescent lamp, the direction of conventional current is from the positive terminal to the negative terminal of the cell. Reversing the connections on the lamp does not change its ability to glow because the lamp is non-polarized. Therefore, the lamp will continue to glow as long as the circuit remains complete, even if the terminals are switched.

Key Concept: Function of the Filament in an Incandescent Lamp

c) The filament glows and emits light
[Solution Description] When electric current flows through the filament of an incandescent lamp, it heats up due to its resistance to the flow of electricity. As the filament gets hot, it begins to glow, emitting light. This process of heating and glowing is what produces light in an incandescent lamp.

Key Concept: Structure of Incandescent Lamp

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that the filament in an incandescent lamp is made of a thin wire that glows when current passes through it. This is true as per the syllabus, which mentions that the filament gets hot and glows to produce light. The reason states that the filament is connected to two thick wires which are fixed to the metal base terminals to allow current flow. This is also true because the syllabus describes how the filament is attached to thicker wires connected to the terminals (metal case and metal tip). Moreover, the reason correctly explains why the filament glows—because it is connected to terminals allowing current flow. Thus, both assertion and reason are true, and the reason is the correct explanation of the assertion.

Key Concept: Electrical Circuit and Filament

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that the filament of an incandescent lamp glows when current flows through it, which is correct as per the syllabus. The reason provided is also true because the filament is connected to the terminals of the electric cell, completing the circuit and allowing current to flow. Moreover, the reason correctly explains the assertion since the glowing of the filament occurs due to the current passing through it in a complete circuit.

Key Concept: Working: filament glows when current flows

a) Filament
[Solution Description]
In an incandescent lamp, the filament is the thin wire that gets heated up and emits light when an electric current passes through it. The resistance of the filament causes it to heat up and glow brightly.

Key Concept: Understanding electrical circuit connection

a) It increases the brightness of the LED.
[Solution Description] Connecting two cells in series increases the total voltage across the LED. According to Ohm's Law ($V = IR$), increasing the voltage while maintaining resistance would increase the current, causing the LED to shine brighter. Hence, using two cells in series provides more power, resulting in increased brightness of the LED.

Key Concept: Direction of electric current

b) From positive terminal to negative terminal
[Solution Description] Conventional current is considered to flow from the positive terminal to the negative terminal of a power source. Even though electrons physically move from negative to positive, convention uses positive to negative direction. Therefore, in a functioning LED circuit, the conventional current flows from the positive terminal of the battery through the LED to the negative terminal.

Key Concept: LED Connection for Lighting

a) Positive terminal of LED connects to positive battery, negative to negative
[Solution Description]
An LED lights up only when its positive terminal (longer wire) is connected to the positive terminal of the battery and its negative terminal (shorter wire) is connected to the negative terminal of the battery. This completes the correct circuit orientation for current flow through the LED.

Key Concept: LED Properties

b) Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.
[Solution Description]
The assertion states that an LED does not have a filament inside it, which is correct because LEDs are semiconductor devices and do not rely on heating a filament to produce light. The reason explains that LEDs operate based on the movement of electrons in a semiconductor material, which is also true. However, the reason does not explicitly explain why there is no filament; it describes how LEDs function differently from incandescent lamps. Thus, both statements are true, but the reason does not directly explain the assertion.

Key Concept: Circuit Components, Electric Cells

c) There may be a break in the circuit
[Solution Description] When a correctly assembled circuit fails to light up the LED despite all components being functional, the issue might lie with the circuit continuity or external influences such as insufficient voltage. The electric cell's positive and negative terminals must align with those of the LED. However, if there is a break in the circuit path due to loose connections or insulation impeding conductor touch, the LED will not light up. Additionally, verifying that the cell provides adequate voltage is essential since it might be depleted.

Key Concept: Understanding LED and battery connection, Circuit Design

c) The LED will not glow
[Solution Description] The LED has two terminals, positive (longer wire) and negative (shorter wire). For the LED to glow, the current must flow from the positive terminal of the battery through the positive terminal of the LED and return to the negative terminal of the battery via the shorter wire (negative terminal of the LED). Interchanging the wires connected to the LED's terminals means that both terminals are incorrectly aligned to the cell's terminals. Since LEDs only allow current flow in one direction, reversing the connections makes the LED not glow.

Key Concept: Directional Current Flow in LED

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that an LED glows under specific polarity conditions, which is correct based on the syllabus. The reason explains why this happens: current flows unidirectionally in an LED. Since the assertion is true and the reason correctly explains it, the correct option is where both are true and the reason justifies the assertion.

Key Concept: LED Connection in Circuit

a) Longer wire of LED to positive battery terminal, shorter wire to negative battery terminal.
[Solution Description] To ensure the LED lights up, it should be connected such that its longer wire (positive terminal) connects to the positive terminal of the battery, and its shorter wire (negative terminal) connects to the negative terminal of the battery. This allows the current to flow in the correct direction through the LED.

Key Concept: Direction of Current Flow

b) From the positive terminal to the negative terminal of the cell
[Solution Description]
Conventional current flows from the positive terminal to the negative terminal of the electric cell. This convention was established based on early assumptions before the actual electron flow direction (negative to positive) was understood. Thus, in diagrams and explanations, we describe current as moving from positive to negative.

Key Concept: Electric Circuit, Current Flow

b) The current decreases
[Solution Description] According to Ohm’s Law, $V = IR$, where $V$ is the voltage, $I$ is the current, and $R$ is the resistance. In this scenario, since the voltage $V$ provided by the battery is constant, any increase in filament resistance $R$ will inversely affect the current $I$. The formula rearranges to give us $I = \frac{V}{R}$. Therefore, if $R$ increases, $I$ must decrease because they are inversely proportional when $V$ is constant.

Key Concept: Electric Circuit Components

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that the lamp will not glow if the circuit is incomplete or connections are incorrect. This is true because for the lamp to glow, there must be a continuous path for current to flow from the positive terminal of the cell/battery to the negative terminal via the lamp. If any part of the circuit is disconnected or incorrectly connected, the current cannot flow, and the lamp will not glow.
The reason explains that the filament of the lamp glows only when current passes through it. This is also true because the heating effect of the current causes the filament to heat up and emit light. Furthermore, the reason correctly explains why the assertion is true—the lamp glows only if current flows through the filament, and current flows only in a complete and correctly connected circuit.
Hence, both the assertion and reason are true, and the reason is the correct explanation of the assertion.

Key Concept: Electric Cell Polarity

a) A small protruding metal cap
[Solution Description]
The positive terminal of an electric cell is marked with a "+" sign and can be identified by the small protruding metal cap on one side. This is opposite to the flat metal disc, which represents the negative terminal.

Key Concept: Effect of broken component

d) Neither lamp will glow
[Solution Description] In a series circuit, the current flows through each component sequentially. If the filament of one lamp breaks, it interrupts the entire circuit, stopping the current flow. As a result, both lamps will not glow because the circuit is no longer complete.

Key Concept: Glowing condition of a lamp

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
From the syllabus, the lamp glows when both terminals are correctly connected to the cell, forming a complete path for current. This matches the Assertion. The Reason states that the lamp glows only when current flows in a complete circuit, which is also true. Since the Reason correctly explains why the lamp glows under the condition mentioned in the Assertion, both statements are true and related.

Key Concept: Complete Circuit, Filament Integrity

c) The lamp terminals are reversed (positive to negative and vice versa).
[Solution Description]
To determine why the lamp is not glowing despite correct connections, we analyze each option:
1. Fused lamp: If the filament is broken, current cannot flow, so the lamp will not glow.
2. Insulator-covered wires: Insulators prevent current flow, so the circuit remains incomplete.
3. Reversed terminals: Incandescent lamps glow regardless of terminal polarity, so reversing terminals does not affect operation.
4. Low cell voltage: If the cell does not provide sufficient voltage, the lamp may not glow.
Thus, the incorrect reason is reversed terminals since polarity does not matter for incandescent lamps.

Key Concept: Complete Circuit

b) Because the circuit becomes complete allowing current to flow
[Solution Description]
A lamp glows when its terminals are correctly connected to those of an electric cell because this setup completes the electrical circuit, providing a path for the electric current to flow through the lamp's filament. The lamp will only glow if the circuit is complete and current flows through it.

Key Concept: Circuit Diagram Symbols

c) To standardize representations internationally
[Solution Description] Symbols in circuit diagrams standardize the representation of electrical components, making it easier for people worldwide to understand and communicate effectively about circuits. This uniformity simplifies both design and troubleshooting processes.

Key Concept: Battery Configuration, Switch Functionality

c) The lamp does not glow due to insufficient net voltage.
[Solution Description]
Cells in series add their voltages when correctly aligned (+ to -). Reversing one cell opposes the others, reducing total voltage.
Step 1: Normal series connection: Total voltage = 3V (assuming V per cell).
Step 2: One reversed cell cancels another’s voltage: Net voltage = V (3V - 2V).
Step 3: Lamp may not glow as insufficient voltage is provided to overcome its resistance.

Key Concept: Direction of current

b) From the positive to the negative terminal of the cell
[Solution Description] The direction of electric current in a simple electrical circuit is conventionally taken to be from the positive terminal of the electric cell to the negative terminal. When connected properly, current flows through the lamp's filament causing it to glow.

Key Concept: Directional Nature of Current Flow, Electric Field Influence

b) The lamp becomes brighter
[Solution Description] Reducing the resistance in a circuit increases the current flow according to Ohm's Law, represented by $I = V/R$, where $I$ is the current, $V$ is the voltage and $R$ is the resistance. With decreased resistance, more current passes through the filament of the lamp. The increase in current results in more energy being delivered per unit time, causing the filament to get hotter and emit more light, thus increasing the brightness of the lamp. Therefore, reducing resistance enhances the brightness of the lamp.

Key Concept: Circuit completion, Lamp glowing condition

c) The current flows from negative to positive terminal inside the battery.
[Solution Description]
For the lamp to glow, there must be a complete path for current from the positive terminal to the negative terminal of the battery. If the lamp does not glow, possible reasons include: disconnected wires (open circuit), incorrect polarity (though lamps usually work both ways), or a burnt-out filament. However, the direction of current flow (conventional vs. actual electron flow) does not affect whether the lamp glows; it’s the completion of the circuit that matters.

Key Concept: Direction of Electric Current and LED behavior

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
According to the syllabus, the direction of electric current in a circuit is conventionally from the positive to the negative terminal of the battery. The assertion states that an LED glows only when connected correctly—positive terminal of LED to positive terminal of battery and negative terminal of LED to negative terminal of battery. This is true because LEDs are unidirectional devices and allow current to pass only in one direction. The reason explains that the conventional current direction is from positive to negative terminal, which is correct, and also mentions the unidirectional property of LEDs, which directly supports why the LED glows under the specified condition. Hence, both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

Key Concept: Direction of Electric Current

b) From the positive terminal to the negative terminal
[Solution Description] In an electric circuit with a single cell, the conventional direction of electric current is considered to flow from the positive terminal to the negative terminal of the cell.

Key Concept: Circuit completeness, filament function

b) The circuit is incomplete preventing current flow
[Solution Description]
For a lamp to glow, current must flow through its filament continuously, requiring a complete circuit. If one terminal is disconnected, the circuit is incomplete, so no current flows and the filament doesn't glow. The correct answer involves recognizing that the circuit must be closed for current to flow.

Key Concept: Circuit Completion, Switch Functionality

b) The switch is not fully disconnecting the circuit
[Solution Description]
When the switch is in the $OFF$ position, the circuit should ideally be open, preventing current flow. However, if the bulb glows faintly, there might be an unintended conductive path or partial contact allowing small current leakage. Possible reasons include a faulty switch (not completely breaking the circuit), moisture causing partial conduction, or high voltage leakage due to damaged insulation. The most plausible explanation among basic circuits is a minor incomplete break in the switch's connection.

Key Concept: Construction of a Simple Switch

c) It acts as a contact point for closing the circuit
[Solution Description] The second drawing pin acts as one of the contact points necessary for completing the circuit. When the free end of the safety pin touches this pin, it closes the circuit, allowing current to flow through the connected device.

Key Concept: Concept of Open and Closed Circuits

d) The circuit is open
[Solution Description] When the safety pin does not make contact with the second drawing pin, there is an air gap that prevents current from flowing through the circuit. This describes an open circuit because the path for electricity is incomplete, thus preventing any electrical flow. Hence, the lamp will not light up as the circuit is in the OFF position.

Key Concept: Circuit completion, Switch functionality

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that in a simple homemade switch, the lamp does not glow when the safety pin is not touching both drawing pins. This is true because when the safety pin does not touch the second drawing pin, the circuit remains open (OFF position), and no current flows through the bulb.
The reason states that an open circuit prevents the flow of electric current, making the bulb not glow. This is also true because, in an open circuit, there is no complete path for current to flow from the positive terminal to the negative terminal of the cell.
Additionally, the reason correctly explains the assertion because the lack of current flow (due to the open circuit) directly causes the bulb not to glow. Hence, both the assertion and reason are true, and the reason is the correct explanation of the assertion.

Key Concept: Symbol Recognition in Circuit Diagrams

b) An open line representing a break
[Solution Description] In a circuit diagram, symbols are used to represent various components. For a switch, the symbol showing a break or an open line indicates its OFF position. This symbolizes that the circuit is not complete, which corresponds to the physical condition where an actual switch breaks the connection between two points, thus preventing the flow of electric current.

Key Concept: Identifying Circuit Behavior with Switches

b) The circuit completes, enabling current to flow and light up the bulb
[Solution Description] When a switch is moved to the ON position in a circuit, it closes the circuit. This means that the previously introduced air gap by the OFF position is now eliminated, forming a complete conductive path. As a result, electricity can flow from the positive terminal of the battery through the entire circuit and back to the negative terminal. Consequently, devices such as bulbs would light up because the closed circuit allows current to pass through them.

Key Concept: Understanding the Function of a Switch

c) The circuit breaks and stops current flow
[Solution Description] When a switch is in the OFF position, it means that the circuit is open. An open circuit does not allow current to flow through it because the path for the electric charges is incomplete. This prevents any connected devices, such as a lamp, from operating because they require a closed loop to function.

Key Concept: Role of a Switch in ON Position

b) Closes the circuit and allows current flow
[Solution Description] A switch in the ON position closes the circuit, creating a continuous path for the electric charges to move through. This allows electricity to flow from the positive terminal to the negative terminal of a power source, thereby enabling any connected device or appliance to function properly.

Key Concept: LED Circuit Analysis

c) The current flows in the direction of the triangle in its symbol
[Solution Description]
The syllabus states that the triangle in the LED symbol points to the direction of current flow. For the LED to glow, the current must flow in the direction indicated by the triangle, meaning the positive terminal of the battery must be connected to the side of the LED where the triangle points.

Key Concept: Circuit Diagrams

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
From the syllabus: The long line in the symbol of an electric cell represents the positive terminal, and the short line represents the negative terminal. This is a standardized representation as per international organizations like IEC, ANSI, and IEEE to maintain uniformity across different regions and industries.
The assertion correctly states the representation of terminals in an electric cell symbol, and the reason accurately explains that such standardization is done by organizations like IEC for global consistency. Hence, both the assertion and reason are true, and the reason correctly explains the assertion.

Key Concept: Circuit diagram definition

c) Circuit diagram
[Solution Description]
The syllabus defines a representation of an electrical circuit using symbols as its circuit diagram.

Key Concept: Switch in ON/OFF position, Battery, Wire

b) Current stops immediately
[Solution Description]
The standard symbol for a switch in the 'OFF' position indicates an open circuit, meaning no current flows. The 'ON' position closes the circuit, allowing current flow.

Key Concept: Electric Cell Function

b) To provide electrical energy
[Solution Description]
An electric cell is a portable source of electrical energy. It provides the necessary voltage/current to power devices connected in a circuit.

Key Concept: Source of Electrical Energy

c) Electrical energy
[Solution Description]
An electric cell is a portable source of electrical energy. It supplies the necessary power for the circuit to function.

Key Concept: Battery Connection

d) Assertion is false, but Reason is true.
[Solution Description]
From the syllabus, it is clear that for a lamp to glow, the cells must be connected in the correct order (positive terminal of one cell to the negative terminal of the next cell). Reversing the direction of even one cell breaks this connection, disrupting the flow of current and preventing the lamp from glowing. Therefore, the Assertion is false because reversing any cell's direction stops the lamp from glowing. The Reason is true since proper connection is essential for current flow.

Key Concept: Types of Batteries

b) Button cells
[Solution Description]
Button cells are small, round batteries typically used in devices like watches and hearing aids because of their compact size and ability to provide steady power for long periods. Cylindrical batteries are used in larger devices like torchlights, while rechargeable batteries are used in high-drain devices like mobile phones.

Key Concept: LED Terminals

d) Positive terminal
[Solution Description]
An LED has two terminals: the positive terminal is attached to a longer wire, while the negative terminal is attached to a shorter wire.

Key Concept: Circuit Completion for Lamp Glow

c) When both terminals are connected correctly
[Solution Description]
An incandescent lamp glows when one terminal of the lamp is connected to one terminal of the electric cell and the other terminal of the lamp is connected to the other terminal of the cell, forming a complete circuit.

Key Concept: LED Connection and Functioning

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
According to the syllabus, an LED lights up only when its positive terminal (longer wire) connects to the positive terminal of the battery and its negative terminal (shorter wire) connects to the negative terminal of the battery. This means the LED must be forward-biased to allow current flow and emit light. If the connection is reversed (positive terminal of LED to negative terminal of battery), no current flows and the LED does not glow. The Assertion states a correct fact about the incorrect connection preventing the LED from glowing. The Reason correctly explains why this happens by stating the condition for current flow in an LED (forward-biasing). Therefore, both Assertion and Reason are true, and Reason correctly explains the Assertion.

Key Concept: Circuit Diagram Symbol

a) Direction of current flow
[Solution Description]
The syllabus explains that the LED symbol is represented by a triangle with arrows indicating light emission, where the triangle points in the direction of current flow.

Key Concept: Switch Placement

c) Anywhere in the circuit
[Solution Description]
A switch can be placed anywhere in an electrical circuit because its function is to either complete or break the circuit. Its position does not affect its ability to control the flow of current.

Key Concept: Switch Functionality

d) Generates electric current when turned ON
[Solution Description]
A switch is used to either complete or break a circuit, allowing or preventing current flow respectively. It does not generate current but controls its flow. Option d) incorrectly states that a switch generates current.

Key Concept: Wire Insulation

b) To protect people from electric shocks
[Solution Description]
Plastic and rubber are excellent insulators that do not conduct electricity. They are used to cover wires primarily to prevent electric shocks when people come into contact with the wires. The insulation also protects against short circuits and environmental factors, but safety is the main concern.

Key Concept: Circuit Symbols

c) The direction of current flow
[Solution Description]
According to the syllabus (Fig. 3.13b), in the symbol for an LED, the triangle points to the direction in which current can flow through the LED. The arrows represent light emission, but the question specifically asks about the triangle's meaning.

Key Concept: Circuit Diagrams: International Standard Symbols

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that using international standard symbols in circuit diagrams ensures easy understanding across different countries and industries. This is true because standardized symbols eliminate confusion and allow engineers and technicians worldwide to interpret circuit diagrams correctly. The reason mentions that international organizations like IEC, ANSI, and IEEE create these standard symbols to promote uniformity in communication. This is also true and directly explains why the assertion holds—standardization by recognized bodies ensures global consistency in symbol usage. Thus, both the assertion and reason are true, and the reason correctly explains the assertion.

Key Concept: Importance of International Standard Symbols

c) International Electrotechnical Commission (IEC)
[Solution Description]
International organizations such as the International Electrotechnical Commission (IEC), American National Standards Institute (ANSI), and the Institute of Electrical and Electronics Engineers (IEEE) are responsible for creating these standard symbols.

Key Concept: LED, Battery, Switch

c) A battery symbol with the long line connected to a closed switch, followed by an LED whose triangle points towards the battery’s short line
[Solution Description]
Since the LED's triangle must point in the direction of current flow (from positive to negative), it should be aligned such that its triangle points towards the negative terminal when connected in series. The switch symbol should be shown as closed (ON position). The battery's long line (+) must connect to the side opposite the LED's triangle.

Key Concept: Electrical Conductors

c) The object is a poor conductor of electricity.
[Solution Description]
If the bulb glows dimly, it means that the material allows some electric current to pass through but offers high resistance. This indicates that the material is a poor conductor (not a good conductor or insulator).

Key Concept: Safety in Handling Electricity

c) Plugging devices with dry hands
[Solution Description]
Since the human body is a conductor of electricity, precautions must be taken to avoid electric shocks. Let's evaluate each option:
1. Using electrical appliances with wet hands: Unsafe, as water increases conductivity, leading to shocks.
2. Touching a frayed wire: Unsafe, as damaged insulation exposes live wires.
3. Plugging devices with dry hands: Safe, as dry skin has higher resistance to current.
4. Standing on a wet floor while using an appliance: Unsafe, as moisture facilitates current flow.
The only safe action among the given options is plugging devices with dry hands.

Key Concept: Electrical Insulators

d) Assertion is false, but Reason is true.
[Solution Description]
The Assertion states that rubber is used to cover electrical wires because it is a good conductor of electricity. This is false because rubber is actually an insulator and does not conduct electricity. The Reason correctly states that insulators like rubber prevent electric shocks by blocking the flow of current, which is true. Since the Assertion is false but the Reason is true, the correct option is (d).

Key Concept: Conductor Identification

b) It is a poor conductor
[Solution Description]
Pencil lead is made of graphite, which is a semi-conductor. Unlike perfect conductors (e.g., metals), graphite allows some current to pass but with resistance, leading to a dim glow in the lamp. Hence, it is neither a good conductor nor a perfect insulator.

Key Concept: Electrical Conductors and Insulators

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that a lamp does not glow when connected to a circuit using a wooden stick. This is true because wood is an insulator, as shown in Table 3.3 of the syllabus, where wooden objects do not conduct electricity. The reason states that wood is an insulator and does not allow electric current to flow, which is also true and directly explains why the lamp does not glow. Therefore, both the assertion and reason are true, and the reason correctly explains the assertion.

Key Concept: Insulators

c) Plastic
[Solution Description]
Plastic, rubber, and ceramics are insulators. They are used to cover electrical wires to protect people from electric shocks.

Key Concept: Conductors and Insulators

c) Ceramic
[Solution Description]
Plug tops must be covered with insulating materials to prevent electric shocks. Among the options, ceramic is the best insulator because it does not conduct electricity and can withstand high temperatures.