Key Concept: Light Travel

c) In a straight line
[Solution Description]
Light travels in a straight line from the source to the object. This is a fundamental property of light as mentioned in the syllabus.

Key Concept: Light Pollution

c) Disruption in communication
[Solution Description]
Light pollution disrupts natural habitats by masking the light signals of fireflies, which they use for communication and mating. Excessive artificial light confuses them, leading to population decline.

Key Concept: Luminous and Non-luminous Objects, Reflection of Light

a) Moon (Non-luminous), LED lamp (Luminous), Venus (Non-luminous), burning candle (Luminous)
[Solution Description]
The Moon and Venus are non-luminous because they reflect sunlight. An LED lamp and a burning candle are luminous since they emit their own light. Thus, the correct classification is:
Luminous: LED lamp, burning candle; Non-luminous: Moon, Venus.

Key Concept: Reflection, Artificial Light

c) LED light is direct emission, whereas moonlight is reflected sunlight with reduced intensity
[Solution Description]
An LED lamp emits its own light directly, while moonlight is reflected sunlight, which loses intensity after reflection. Additionally, the LED lamp is closer to the observer compared to the Moon, making it appear brighter despite its smaller size.

Key Concept: Non-Luminous Objects

c) Non-luminous object
[Solution Description]
Non-luminous objects do not emit their own light but reflect light from other sources. The Moon reflects sunlight, so it is classified as a non-luminous object.

Key Concept: Natural Light Sources, Historical Context

c) Natural light cannot be used at all times
[Solution Description]
Analyzing the options based on historical progression and advantages of artificial light sources:
1. **Greater Control and Convenience**:
Natural light sources like fire or sunlight are inconsistent and uncontrollable (e.g., no sunlight at night). Artificial lighting provides reliable illumination anytime.
2. **Technological Advancements**:
Invention of electricity and modern lighting technologies (like gas lamps, later electric bulbs) made artificial lighting more efficient and widespread.
3. **Environmental Factors** (incorrect option):
While LEDs are eco-friendly now, earlier artificial sources (like kerosene lamps) were not necessarily better for the environment than fire.
The primary reason was greater control over illumination and convenience, as natural sources were limiting.

Key Concept: Properties of Light

b) It reflects sunlight
[Solution Description]
The Moon is a non-luminous object, meaning it does not emit its own light. It appears bright because it reflects the sunlight falling on its surface. This reflection allows us to see the Moon from Earth.

Key Concept: Luminous Objects

d) Assertion is false, but Reason is true.
[Solution Description]
The Assertion states that the Moon is a luminous object emitting its own light, which is false. The Moon does not emit its own light; it reflects sunlight. Therefore, it is a non-luminous object. The Reason correctly defines luminous objects as those that emit their own light and can be seen in the dark. However, this correct reason does not explain the incorrect assertion about the Moon.

Key Concept: Gas lamps, Heat energy conversion

b) 165 kJ
[Solution Description]
Total energy from 0.5 moles of propane:
$0.5 \text{ moles} \times 2200 \text{ kJ/mole} = 1100 \text{ kJ}$
Light energy produced (15\% efficiency):
$1100 \text{ kJ} \times 0.15 = 165 \text{ kJ}$

Key Concept: LED lamps, Energy efficiency, Environmental impact

b) \$1,095,000
[Solution Description]
First, calculate the power consumed by incandescent bulbs annually:
$100,000 \times 60 \text{ W} = 6,000,000 \text{ W} = 6000 \text{ kW}$
Daily energy consumption: $6000 \text{ kW} \times 5 \text{ h} = 30,000 \text{ kWh}$
Annual energy consumption: $30,000 \text{ kWh/day} \times 365 \text{ days} = 10,950,000 \text{ kWh}$
Now, calculate for LED bulbs:
$100,000 \times 10 \text{ W} = 1,000,000 \text{ W} = 1000 \text{ kW}$
Daily energy consumption: $1000 \text{ kW} \times 5 \text{ h} = 5000 \text{ kWh}$
Annual energy consumption: $5000 \text{ kWh/day} \times 365 \text{ days} = 1,825,000 \text{ kWh}$
Energy saved: $10,950,000 - 1,825,000 = 9,125,000 \text{ kWh}$
Cost saving: $9,125,000 \text{ kWh} \times 0.12 \text{ \$/kWh} = \$1,095,000$

Key Concept: Luminous vs. Non-luminous objects

b) It emits its own light
[Solution Description]
A luminous object emits its own light, unlike non-luminous objects that reflect light from other sources.

Key Concept: Luminous vs. Non-luminous, Real-world application

d) LED lamps save energy and reduce environmental pollution.
[Solution Description]
LED lamps consume much less power compared to traditional lamps while providing brighter light. They also have a longer lifespan, reducing waste generation. This leads to lower electricity bills and fewer resources spent on manufacturing replacements. Additionally, LEDs reduce environmental impact due to lower energy consumption, which decreases greenhouse gas emissions from power plants. Proper disposal or recycling at their end-of-life ensures minimal environmental harm.

Key Concept: Non-Luminous Objects, LED Technology, Science & Society

b) Unlike the Moon, LEDs emit their own light, making them luminous.
[Solution Description]
The Moon reflects light (non-luminous), whereas LEDs emit their own light (luminous). However, both topics involve understanding how light behaves—either reflected or emitted. Government efforts emphasize efficiency (LEDs), just as understanding reflection helps explain why the Moon is visible without self-emission.

Key Concept: Sources of Light

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The syllabus states that objects emitting their own light are called luminous objects, while those that do not are non-luminous. The Moon does not emit light but reflects sunlight, making it non-luminous. Therefore, both the assertion and reason are true, and the reason correctly explains the assertion.

Key Concept: Light travels in a straight line

c) A laser beam in water appears as a straight line
[Solution Description]
All given options relate to light behavior, but only one directly shows light traveling in a straight line. A laser beam passing through water follows a visible straight path, providing direct evidence of this property.

Key Concept: Light Travel, Matchbox Activity, Candle Flame Experiment

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The Assertion states that light travels in a straight line based on the matchbox activity where light passes only when holes are aligned. This is correct as per the syllabus observation. The Reason provides another experiment (candle flame through a bent pipe) to support the same conclusion. Both activities independently confirm that light travels in a straight line, making the Reason a correct explanation of the Assertion.

Key Concept: Matchbox hole experiment, alignment of holes

c) The spot disappears
[Solution Description]
The bright spot appears only when all three holes are perfectly aligned in a straight line, allowing light to pass through them uninterrupted. Raising the middle matchbox misaligns its hole, blocking the light path. Therefore, the spot on the screen disappears.

Key Concept: Observation from experiment

c) No light spot appears on the screen
[Solution Description]
When one matchbox is moved out of alignment, the light path is blocked because light travels in straight lines and cannot bend to go through misaligned holes. Therefore, no spot appears on the screen.

Key Concept: Light propagation, Straight vs. Bent Pipe

d) The exact angle depends on the pipe's length and diameter
[Solution Description]
The experiment shows that light travels in a straight line and cannot bend around corners. As the pipe is gradually bent, the point where the flame disappears corresponds to the angle at which light can no longer travel directly from the flame to the observer's eye due to the obstruction caused by the bend. This occurs when the inner walls of the pipe block the direct path of light. Therefore, the flame first disappears when the pipe is bent just enough to obstruct the straight-line path of light.

Key Concept: Experiment Conclusion

c) Light travels in a straight line
[Solution Description] The observation confirms that light travels in a straight line since it can pass through a straight pipe but not a bent one, where its path is obstructed.

Key Concept: Light travels in a straight line, Matchbox experiment

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that if three matchboxes are arranged non-linearly, no light will pass through all the holes. This is true because light travels in a straight line, as demonstrated by the matchbox experiment in Activity 11.1. When the holes are not aligned, light cannot travel through all of them. The reason explains that light travels in a straight line unless obstructed or refracted, which is also true. The reason correctly explains the assertion since the inability of light to pass through non-aligned holes is due to its straight-line propagation property.

Key Concept: Light travel, Shadow formation

b) The light spot disappears.
[Solution Description]
When all three pinholes are aligned in a straight line, light passes through them and forms a bright spot on the screen. If the middle pinhole is moved upward, the alignment is broken. Light from the torch passes through the first hole but cannot pass through the misaligned second hole, preventing it from reaching the screen. Thus, no spot will be seen.

Key Concept: Transparent Materials

c) Glass
[Solution Description]
Transparent materials, like glass, allow almost all light to pass through them. From Table 11.1, glass is classified as transparent and permits full light transmission.

Key Concept: Translucent Materials

b) Tracing paper
[Solution Description]
Translucent materials, such as tracing paper, let some light pass but not fully. From Table 11.1, tracing paper is translucent and transmits light partially.

Key Concept: Transparent Materials

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that glass allows light to pass through it completely, enabling clear visibility of objects behind it. This is true because transparent materials, such as glass, permit almost all incident light to pass through them without significant scattering or absorption. The reason claims that transparent materials like glass do not scatter or absorb any significant amount of light, which is also correct and directly explains why the assertion is true. Therefore, both the assertion and reason are true, and the reason correctly explains the assertion.

Key Concept: Light Transmission

c) Translucent
[Solution Description]
Translucent materials allow light to pass partially but do not allow objects to be seen clearly. From the syllabus, tracing paper is an example of a translucent material. Transparent materials allow clear visibility, while opaque materials block light completely. Thus, the correct answer must describe a translucent material.

Key Concept: Translucent Materials

c) Oiled paper
[Solution Description]
According to the syllabus, translucent materials partially allow light to pass through. Oiled paper is given as an example of a translucent material in the syllabus.

Key Concept: Light transmission, Shadow formation

c) Light intensity decreases due to cumulative scattering by both materials.
[Solution Description]
When light passes through the first translucent material, it gets scattered and only a portion reaches the screen. Placing a second identical translucent material further reduces the intensity because scattering occurs again. Thus, the total transmitted light decreases multiplicatively.
Problem-solving steps:
- Light incident on first material: $I_0$.
- Light passing through first material: $T \cdot I_0$, where $T < 1$ is the transmittance.
- Light passing through second material: $T \cdot (T \cdot I_0) = T^2 I_0$.
Hence, the final light intensity reaching the screen is reduced.

Key Concept: Shadow Formation

c) A transparent object
[Solution Description]
According to syllabus observations in Activity 11.4, three things are needed to form a shadow: a light source, an opaque object, and a screen. A transparent object isn't needed as it would allow light to pass through.

Key Concept: Shadow Size

c) Shadow becomes smaller
[Solution Description]
Table 11.2 in the syllabus clearly states that when the object is moved closer to the torch (with screen fixed), the shadow becomes smaller. This occurs because more light can go around the object when it's nearer the source.

Key Concept: Laser beam visibility

c) The laser beam becomes visible and follows a straight path.
[Solution Description]
The laser beam becomes visible due to the scattering of light by milk particles. The path of the beam inside the water appears straight because light travels in a straight line.

Key Concept: Light Travel, Laser Beam Visibility in Medium

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that adding milk to water makes a laser beam visible, confirming its straight-line travel. This is true because milk particles scatter light, making the beam observable. The reason correctly explains this phenomenon by connecting the visibility effect to scattering and rectilinear propagation, both valid concepts from the syllabus. Hence, both statements are true, and the reason justifies the assertion.

Key Concept: Shadow Properties

b) Color of the shadow
[Solution Description]
The color of a shadow depends on the opacity of the object blocking the light, not on the color of the object itself. Changing the color of the object does not alter the color of the shadow; it remains dark or faint depending on the opacity.

Key Concept: Shadow Formation

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The Assertion states that translucent objects cast lighter shadows compared to opaque objects. This is true because translucent objects partially transmit light, leading to less intense shadows. The Reason explains that translucent objects allow some light to pass through, while opaque objects block all light, which is a correct explanation for why translucent objects form lighter shadows. Both statements are true, and the Reason logically justifies the Assertion.

Key Concept: Shadow Characteristics

d) The color of the shadow is always black regardless of the object's color
[Solution Description]
Shadows are formed when light is blocked by an opaque object. The color of the object does not affect the color of the shadow; it only affects the darkness or lightness of the shadow. Transparent objects do not form dark shadows because they allow most light to pass through. Shadows give information about the shape but not necessarily the exact identity of the object.

Key Concept: Shadow Formation

c) The shadow becomes larger
[Solution Description]
When an opaque object is placed closer to the light source, the angle at which light is blocked increases. This causes the shadow to become larger on the screen. The size of the shadow depends on the distance between the light source and the object. As the object moves closer to the light source, the shadow enlarges because more light is obstructed from reaching the screen.

Key Concept: Basic Components of Shadow Formation

b) Light source, opaque object, screen
[Solution Description]
To form a shadow, we need:
1. A source of light (e.g., torch, sun).
2. An opaque object that blocks the light.
3. A screen (e.g., wall, floor) where the shadow is observed.
These are the only necessary components for shadow formation.

Key Concept: Shadow formation, Multiple light sources

d) Two overlapping shadows form an umbra and penumbra
[Solution Description]
With two light sources, each casts its own shadow of the sphere on the screen. These shadows overlap partially. In the overlapping region, no light reaches the screen because both light sources are blocked, creating a darker area called the umbra. Outside the umbra but within individual shadows, only one light source is blocked, creating lighter regions called penumbrae. Thus, there will be two penumbral regions and a central umbral region where both shadows overlap. The exact pattern depends on the distances between the lights, object, and screen, but the key feature is the presence of distinct umbra and penumbra zones.

Key Concept: Luminous and Non-Luminous Objects

d) Assertion is false, but Reason is true.
[Solution Description]
The Assertion states that the Moon is a luminous object, which means it emits its own light. However, according to the syllabus, the Moon does not emit its own light; it reflects sunlight. Therefore, the Assertion is false. The Reason correctly explains that the Moon reflects light from the Sun, which is true as per the syllabus. Hence, the Assertion is false, but the Reason is true.

Key Concept: Shadow Formation

b) The dark region formed where light is blocked by an object
[Solution Description]
A shadow is formed when an opaque object blocks the path of light, creating a dark patch where light does not reach. This happens because light travels in straight lines and cannot bend around the object.

Key Concept: Shadow Characteristics

d) The position of the object relative to the light source and screen
[Solution Description]
From the syllabus: "The shape, size, and sharpness of the shadow depend on the position of the object relative to the light source and the screen."
For example, moving the object closer to the light source makes the shadow larger, while tilting the object changes its shape.

Key Concept: Shadow Formation, Opaque Objects

b) Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.
[Solution Description]
When an opaque object is placed near a light source, more light rays are obstructed compared to when it is farther away. This obstruction leads to a larger area where light does not reach, forming a darker shadow. The closer the object gets to the light source, the more divergent the light rays become, increasing the region of darkness. However, the reason states that the shadow becomes sharper, which is not always true—it depends on the size and nature of the light source. While moving the object closer does make the shadow darker, the sharpness aspect is context-dependent and not universally accurate.

Key Concept: Shadow Formation: Screen

b) Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.
[Solution Description]
To form a shadow, three things are essential: a light source, an opaque object, and a screen. The screen acts as the surface where the shadow is observed. The light is blocked by the opaque object, creating a shadow on the screen. The assertion states that a shadow cannot be formed without a screen, which is true because without the screen, there is no surface to project the shadow onto. The reason states that the screen is necessary to block the light and observe the shadow. This is also true, but incorrect in explaining the assertion. The screen does not block the light; it merely displays the shadow formed due to the blocking of light by the opaque object. Therefore, both Assertion and Reason are true, but Reason does not correctly explain Assertion.

Key Concept: Basic Components for Shadow Formation

c) Light, opaque object, screen
[Solution Description]
To observe a shadow, we need three things: a source of light, an opaque object that blocks the light, and a screen where the shadow is formed. The syllabus clearly states that shadows are formed when an object blocks light from falling on a screen.

Key Concept: Shadow Formation

d) Color of the opaque object
[Solution Description]
The sharpness of a shadow depends on factors like the size of the light source, distance between the object and the screen, and the opacity of the object. However, the color of the opaque object does not affect the sharpness but only changes the appearance of the shadow (e.g., darkness). Thus, changing the color does not impact its sharpness.

Key Concept: Shadow size, Distance variation

b) Decreases by a factor of 2
[Solution Description]
The size of the shadow depends on the relative distances of the light source, object, and screen. Doubling the light-source-to-object distance reduces the angle at which light rays diverge around the object, causing the shadow to become smaller. Specifically, the height of the shadow ($H$) is given by $H = h \left(1 + \frac{D_2}{D_1}\right)$, where $h$ is the object height, $D_1$ is the light-source-to-object distance, and $D_2$ is the object-to-screen distance. If $D_1$ increases, the ratio $\frac{D_2}{D_1}$ decreases, reducing $H$.

Key Concept: Shadow Characteristics

c) Shadow becomes larger
[Solution Description]
When the object moves closer to the light source relative to the screen, the shadow becomes larger in size because the angle at which light is blocked increases, casting a bigger shadow on the screen.

Key Concept: Shadow Formation, Opaque vs Translucent

c) A dark shadow with a faint outer region
[Solution Description]
The opaque sheet will block all light, forming a completely dark shadow. The translucent sheet allows some light to pass through, creating a faint or lighter shadow. Since they are of the same size and placed one after another, both shadows will overlap. The final shadow will have a darker region corresponding to the opaque sheet and a lighter region where only the translucent sheet blocks the light.

Key Concept: Shadow Formation and Color

c) Color of the object
[Solution Description]
The color of a shadow is determined by the absence of light and does not change based on the color of the object blocking the light. According to the syllabus, changing the color of an opaque object does not alter the shadow's color.

Key Concept: Translucent vs. opaque shadows

d) The opaque sheet blocks all light, producing a darker shadow.
[Solution Description]
Translucent materials allow some light to pass through them, resulting in a faint shadow because the screen receives partial illumination. Opaque materials block all light, creating a dark shadow where no light reaches the screen. The color of the sheets is irrelevant to the shadow's darkness; only the opacity affects it.

Key Concept: Shadow Formation - Translucent and Transparent Materials

d) Assertion is false, but Reason is true.
[Solution Description]
The assertion states that all transparent objects form faint shadows. According to the syllabus, some transparent objects can create faint shadows, but not all. Thus, the assertion is false.
The reason states that transparent objects allow most light to pass through but may still block a small amount of light. This is true, as even transparent materials can slightly scatter or absorb light, leading to faint shadows in some cases. Hence, the reason is correct but does not explain the assertion since the assertion itself is incorrect.

Key Concept: Shadow Formation by Translucent Objects

c) A lighter and less defined shadow
[Solution Description]
Translucent objects allow some light to pass through but scatter it, resulting in a lighter shadow compared to opaque objects. Since they do not block all light, the shadow formed will be faint or blurred.

Key Concept: Image Formation by Plane Mirror

b) 10 cm
[Solution Description]
For a plane mirror, the image distance ($d_i$) is equal to the object distance ($d_o$) but on the opposite side of the mirror. Since the object is placed 10 cm in front of the mirror, the image will be formed 10 cm behind the mirror.

Key Concept: Law of Reflection

c) The angle of incidence is equal to the angle of reflection
[Solution Description]
The law of reflection states that the angle of incidence is equal to the angle of reflection, i.e., $\text{Angle of incidence} = \text{Angle of reflection}$.

Key Concept: Reflection, Image Formation

c) 40 cm
[Solution Description]
First, the light from the source travels down to the mirror. The apparent depth due to refraction is calculated as:
$d' = \frac{d}{n} = \frac{20}{1.33} = 15.04 \text{ cm}$ (distance in water).
The light reflects from the mirror and travels back up. The total distance traveled by light in water is $2 \times 15.04 = 30.08 \text{ cm}$.
The apparent height after reflection is again $d'' = d' \times n = 30.08 \times 1.33 = 40 \text{ cm}$.
Therefore, the image appears $40 \text{ cm}$ below the water surface.

Key Concept: Definition of Reflection

c) Reflection of light
[Solution Description]
The change in direction of light when it falls on a shiny surface like a mirror is called reflection of light. This is explicitly mentioned in the syllabus.

Key Concept: Reflection of Light

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that a plane mirror changes the direction of light when it strikes its surface. This is true because, as per the syllabus, reflection is defined as the change in direction of light upon striking a shiny surface like a mirror. The reason given is also true, stating that reflection of light occurs because a shiny surface alters the path of light rays. Moreover, the reason correctly explains why the assertion is true, as the alteration of light's path by a shiny surface is precisely what causes reflection.

Key Concept: Image Characteristics

c) Same size as the object and laterally inverted
[Solution Description]
The syllabus states that the image formed by a plane mirror has specific characteristics: it is of the same size as the object, erect (upright), cannot be obtained on a screen, and is laterally inverted (left-right reversed). These are all properties mentioned under "Additional Notes" in the syllabus.

Key Concept: Image Characteristics

c) The image is of the same size as the object
[Solution Description]
The image formed by a plane mirror is always virtual, erect, and of the same size as the object. It cannot be obtained on a screen and shows lateral inversion. Therefore, the correct answer is that it is of the same size as the object.

Key Concept: Images Formed in a Plane Mirror

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The Assertion states that the image formed by a plane mirror is virtual and cannot be obtained on a screen, which is true as per Activity 11.7. The Reason explains that a virtual image is formed when light rays appear to diverge but do not actually meet, which is also correct. Moreover, the Reason correctly explains why the Assertion is true because virtual images cannot be captured on a screen due to the divergence of light rays.

Key Concept: Lateral Inversion

b) Right hand
[Solution Description]
Due to lateral inversion, the image in a plane mirror appears reversed from left to right. Thus, when you raise your left hand, the image appears to raise its right hand. This is a classic demonstration of lateral inversion in plane mirrors.

Key Concept: Image Distance and Size

d) 20 cm
[Solution Description]
In a plane mirror, the image appears to be as far behind the mirror as the object is in front of it. Therefore, if the object is 10 cm from the mirror, the image will appear to be 10 cm behind the mirror. The total distance between the object and its image is the sum of these two distances: $10\,\text{cm} + 10\,\text{cm} = 20\,\text{cm}$.

Key Concept: Plane Mirror Image Properties

b) Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.
[Solution Description]
The assertion states that the image formed by a plane mirror is always the same size as the object, which is true based on the syllabus observations. The reason explains that the light rays diverge after reflection, forming a virtual image at an equal distance behind the mirror. While this is true, the size of the image being the same as the object is independent of the distance due to the nature of reflection in plane mirrors. Therefore, both statements are true, but the reason does not correctly explain why the image size remains unchanged with varying distances.

Key Concept: Distance of Image from Mirror

b) 5 meters
[Solution Description]
From the syllabus, the distance of the image from the mirror is equal to the distance of the object from the mirror. Therefore, if the object is 5 meters away, the image will appear 5 meters behind the mirror.

Key Concept: Object movement, Image behavior

b) 2 m/s
[Solution Description]
In a plane mirror, the image appears to be as far behind the mirror as the object is in front. When the object moves towards the mirror at 2 m/s, the image also appears to move towards the mirror at the same speed (2 m/s). The relative speed between the object and its image would be 4 m/s when approaching each other, but the question asks for the apparent speed of the image towards the mirror.

Key Concept: Erect Image Formation

d) Erect and same size as the object
[Solution Description]
The image formed by a plane mirror is always erect (upright), virtual, same size as the object, and cannot be obtained on a screen.

Key Concept: Plane Mirror Properties

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The image formed by a plane mirror is virtual because it is formed by the apparent intersection of the reflected rays behind the mirror, not by the actual convergence of light rays. Since virtual images cannot be projected onto a screen, both the assertion and reason are true, and the reason correctly explains the assertion.

Key Concept: Properties of Plane Mirror Images

c) The image is laterally inverted and cannot be captured on a screen.
[Solution Description]
The image formed by a plane mirror is virtual (cannot be captured on a screen), erect, of the same size as the object, and laterally inverted. It is not real or diminished.

Key Concept: Lateral inversion, Real-world application

b) AMBULANCE
[Solution Description]
The word $\text{\textbackslash reflectbox\{ECNALUBMA\}}$ is the laterally inverted form of "AMBULANCE". When viewed in a mirror, it appears correct ("AMBULANCE"). Therefore, the original text is "AMBULANCE".

Key Concept: Laterally Inverted Image in Plane Mirror

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that when a person raises their left hand, the image in a plane mirror appears to raise its right hand. This is true because a plane mirror creates a laterally inverted image, where left and right sides are swapped. The reason explains that a plane mirror causes lateral inversion, which is correct and directly explains the assertion. Therefore, both the assertion and reason are true, and the reason correctly explains the assertion.

Key Concept: Pinhole Camera Image Formation

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that the image formed by a pinhole camera is inverted, which is true as observed in Activity 11.9. The reason explains that light travels in straight lines, causing the inversion because the rays from the top of the object cross at the pinhole and reach the bottom of the screen, and vice versa. This correctly explains the assertion.

Key Concept: Pinhole Camera Image Formation, Light Propagation

b) The image becomes larger and blurrier
[Solution Description]
When the distance between the pinhole and the screen ($d_s$) is increased, the image becomes larger because the light rays spread over a larger area on the screen. However, increasing $d_s$ also reduces the brightness and sharpness of the image because fewer light rays from the object reach each point on the screen. The image remains inverted as long as the pinhole is small enough for straight-line propagation.

Key Concept: Light intensity, Image brightness

d) Decreases by factor of 4
[Solution Description]
The brightness of the image depends on the amount of light passing through the pinhole. Light passing through is proportional to the area of the pinhole. Area is proportional to square of diameter ($A ∝ d^2$). When diameter becomes $\frac{d}{2}$, area becomes $\frac{d^2}{4}$. Therefore, the brightness reduces by factor of 4.

Key Concept: Key observation about pinhole camera

b) Pinhole camera forms inverted image, mirror forms laterally inverted image
[Solution Description]
A pinhole camera forms an inverted image, while a mirror forms a laterally inverted image (left-right reversed but not upside down).

Key Concept: Pinhole Camera, Image Formation, Lateral Inversion

d) Assertion is false, but Reason is true.
[Solution Description]
The assertion states that the image formed by a pinhole camera is both inverted and laterally inverted. However, according to the syllabus, the image formed by a pinhole camera is only inverted (upside down), not laterally inverted. The reason given is correct because the pinhole camera works due to the rectilinear propagation of light, which causes the image to be inverted but not laterally inverted. Therefore, the assertion is false while the reason is true.

Key Concept: Material Used

c) The entire structure of the camera
[Solution Description]
The main body of the pinhole camera is constructed using two cardboard boxes that slide into each other. The larger box has the pinhole, while the smaller box holds the translucent screen. This setup allows adjusting the distance between the pinhole and the screen to focus the image.

Key Concept: Pinhole Camera vs. Plane Mirror Images

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The Assertion states that a pinhole camera forms an inverted image due to the crossing of light rays at the pinhole. This is correct because light from the top of the object passes downward through the pinhole and appears at the bottom of the image, and vice versa, resulting in inversion. The Reason explains why a plane mirror does not invert the image: it reflects light without crossing, producing a laterally inverted but upright image. Both statements are accurate, and the Reason directly explains the difference between the two imaging mechanisms.

Key Concept: Pinhole camera construction

c) Tracing paper
[Solution Description]
The activity specifically mentions using tracing paper (a thin translucent paper) to cover the opening and form the screen where the image appears.

Key Concept: Periscope

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The periscope is designed with two plane mirrors placed at 45-degree angles inside a Z-shaped tube. Light entering from one end hits the first mirror and reflects at 90 degrees to the second mirror. The second mirror then reflects the light again at 90 degrees towards the viewer's eye. This double reflection allows light to bend around obstacles, enabling the viewer to see objects that are not directly visible. Therefore, both assertion and reason are correct, and the reason correctly explains how the periscope works.

Key Concept: Periscope

b) 2 mirrors arranged in a Z-shape
[Solution Description]
A periscope requires two plane mirrors arranged in a Z-shaped configuration to reflect light twice, allowing the user to see around obstacles.

Key Concept: Periscope

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that a periscope uses two plane mirrors at a 45-degree angle to view objects not directly visible. This is true because the Z-shaped arrangement of mirrors allows light to reflect twice, enabling the user to see around obstacles. The reason given is that light travels in a straight line and is reflected by mirrors, which is also correct and explains why the periscope works: the straight-line propagation and reflection principles are fundamental to its operation.

Key Concept: Principle of Reflection in Periscope

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that a periscope uses two plane mirrors at 45° angles, which is correct as per the syllabus. The reason explains that the angle of incidence equals the angle of reflection, which is true for plane mirrors. This principle ensures that light is redirected properly through the periscope, enabling indirect visibility. The reason correctly explains why the arrangement of mirrors at 45° angles works, as it ensures the light exits parallel to its original direction after two reflections. Therefore, both the assertion and reason are true, and the reason correctly explains the assertion.

Key Concept: Periscope Construction

b) Light reflects twice before exiting
[Solution Description]
When two mirrors are placed at a 45\textdegree angle to each other, light undergoes reflection twice before it exits. The first reflection occurs at the first mirror, redirecting the light towards the second mirror. The second reflection occurs at the second mirror, which then allows the light to exit the tube. Thus, there are exactly 2 reflections.

Key Concept: Periscope, Reflection in Mirrors

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
Understanding the behavior of light in a periscope requires analyzing the reflections:
1. When light enters the periscope, it hits the first mirror (Mirror 1) at 45°. The first reflection causes lateral inversion of the image.
2. The reflected light then travels to the second mirror (Mirror 2), also placed at 45°. The second reflection causes another lateral inversion.
3. Two lateral inversions restore the original orientation of the image. Thus, the final image appears as it would without any mirrors.
Therefore, the assertion is true because the final image is not laterally inverted due to double inversion. The reason correctly explains why the final image returns to its original orientation.

Key Concept: Image Formation

d) Seven images are formed
[Solution Description]
When two mirrors are inclined at 45\textdegree, they form multiple images due to successive reflections. The number of images formed is calculated by $\frac{360}{\theta} - 1$, where $\theta$ is the angle between the mirrors. For $\theta = 45\textdegree$, $\frac{360}{45} - 1 = 7$. So, 7 images are formed.

Key Concept: Image Formation by Mirrors

c) The second mirror cancels the inversion caused by the first
[Solution Description]
Each reflection in a mirror causes lateral inversion (left-right reversal). In a periscope, the first mirror reflects the image downward, and the second mirror corrects the orientation by reflecting it back to an upright position. Since both reflections compensate for each other, the final image is not upside-down but only laterally inverted.

Key Concept: Periscope construction, Lateral inversion

b) Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.
[Solution Description]
The assertion correctly states that a periscope uses two plane mirrors in a Z-shape to view obscured objects, which is accurate as per the syllabus. The reason claims that the mirrors are set at 45 degrees and correct lateral inversion through double reflection. While two reflections do occur, the primary purpose is to redirect light, not necessarily to "correct" lateral inversion, as the final image still shows lateral inversion. Thus, the reason is not entirely accurate in its explanation regarding correction of lateral inversion.

Key Concept: Periscope

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that a periscope uses two plane mirrors arranged in a Z-shaped box to see objects not directly visible, which is correct as per the syllabus. The reason explains that the reflection of light from two mirrors allows viewing around obstacles. Both statements are accurate and the reasoning correctly explains how the periscope works by reflecting light twice to see around obstacles.

Key Concept: Construction of Kaleidoscope

c) Plane mirrors or reflective paper strips
[Solution Description]
To construct a basic kaleidoscope, reflective surfaces are needed to create multiple images of the objects inside. Plane mirrors or thick reflective paper strips can be used as they reflect light efficiently. Without these reflective surfaces, the kaleidoscope cannot produce the characteristic patterns.

Key Concept: Mirror Arrangement

c) Three
[Solution Description]
A kaleidoscope uses three rectangular plane mirror strips arranged in a triangular shape to create multiple reflections and beautiful patterns. This is clearly mentioned in the syllabus under "Key Features" and "Materials Needed".

Key Concept: Reflection in Kaleidoscope

c) New patterns are formed due to changing reflections
[Solution Description]
A kaleidoscope contains three rectangular mirrors arranged in a triangular manner. When you rotate it, the arrangement of the broken pieces of colored bangles or beads inside changes. Due to multiple reflections from the three mirrors, new patterns are formed each time because the relative positions of the objects change with rotation.

Key Concept: Mirror reflection property

a) Symmetrical patterns
[Solution Description]
The syllabus explicitly states under Important Observations: "The patterns formed are symmetrical and vary with the arrangement of coloured objects." This results from multiple reflections in the triangular mirror arrangement.

Key Concept: Multiple reflections, Symmetrical patterns

c) 6
[Solution Description]
In a triangular mirror arrangement with 60° angles, the number of virtual images formed is calculated by 360°/angle between mirrors - 1. For equilateral triangle mirrors (60° angle): Number of images = (360/60) - 1 = 6 - 1 = 5. However, due to the closed triangular system, these images further reflect creating a symmetrical pattern with theoretically infinite images. But practically, we see finite distinct images forming hexagonal symmetry, typically observable as 6 main images plus the original object.
The correct mathematical formulation for perfect mirrors gives: N = (360/θ) - 1 where θ is the angle between mirrors. For θ=60°, N=5. But in reality, each of these 5 images reflects again in other mirrors, creating a complex but finite pattern that appears as 6 clearly distinguishable symmetric images around the central object.

Key Concept: Kaleidoscope Principle

b) To create multiple reflections forming symmetric patterns
[Solution Description]
The triangular arrangement of mirrors in a kaleidoscope creates multiple reflections of the colored objects placed at one end. Each reflection from one mirror strikes another, leading to symmetric and beautiful patterns due to repeated reflections. This arrangement ensures that light reflects back and forth between the mirrors, creating an intricate design.

Key Concept: Kaleidoscope Functionality

c) Reflection of light
[Solution Description]
A kaleidoscope works based on the reflection of light. When light falls on the mirrors arranged in a triangular manner, it undergoes multiple reflections, producing beautiful patterns.

Key Concept: Application of Kaleidoscope

c) Designers and artists
[Solution Description]
Designers and artists often use kaleidoscopes to generate new ideas for patterns. The ever-changing symmetric designs provide creative inspiration for textiles, wallpapers, logos, and other artistic projects.

Key Concept: Mirror Arrangement, Symmetry

c) The symmetry increases, creating more complex patterns.
[Solution Description]
The number of reflections in a kaleidoscope depends on the angle between the mirrors. With three mirrors arranged symmetrically at 60 degrees, the pattern repeats every 60 degrees due to the hexagonal symmetry. When the angle is reduced to 45 degrees, the symmetry changes to octagonal because 360 divided by 45 equals 8, meaning the pattern repeats every 45 degrees. Therefore, the symmetry increases, creating more complex and detailed patterns.

Key Concept: Materials Used

b) Broken pieces of colored bangles or beads
[Solution Description]
Broken pieces of colored bangles or beads are placed on the transparent plastic sheet at one end of the kaleidoscope. These objects reflect off the mirrors to create the colorful patterns seen when peeping through the other end.

Key Concept: Kaleidoscope

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The kaleidoscope indeed uses three mirrors arranged in a triangular manner, which causes multiple reflections of the objects placed inside it. Each reflection creates an image, and these images overlap due to the angular arrangement of the mirrors, producing intricate and symmetric patterns. When the kaleidoscope is rotated, the relative positions of the objects and the mirrors change, resulting in new patterns. Therefore, both the assertion and reason are true, and the reason correctly explains why the patterns change when the kaleidoscope is turned.

Key Concept: Kaleidoscope mirror angles, multiple reflections

c) Pattern symmetry increases to 24-fold but appears less distinct
[Solution Description]
In a standard kaleidoscope with three mirrors at 60° angles (equilateral triangle), the pattern has 6-fold symmetry (360°/60°). When one mirror is rotated by 15°, the new angle between adjacent mirrors becomes 45° and 75°. The symmetry changes because the angular divisions are no longer equal. The least common divisor of 45° and 75° is 15°, so the new symmetry order is 360°/15° = 24. However, practical visibility reduces the effective repeating sections due to limited reflection depth.