Unit Test Solutions: Light: Shadows and Reflection | Science (Curiosity) Class 7 - New NCERT PDF Download

Time: 1 Hour

Maximum Marks: 30

Instructions:

Attempt all questions.

Question numbers 1 to 5 carry 1 mark each .
Question numbers 6 to 8 carry 2 marks each.
Question numbers 9 to 11 carry 3 marks each.
Question numbers 12 and 13 carry 5 marks each.

Q1. Which object shines by reflecting light rather than producing it? (1 Mark)
a) Sun
b) Firefly
c) Moon
d) Lightning

Answer: c) Moon
Sol: The Moon is a non-luminous object that shines by reflecting sunlight

Q2. What happens when light passes through a translucent material? (1 Mark)
a) It is completely blocked
b) It passes through clearly
c) It passes through partially, causing blurred visibility
d) It reflects back completely

Answer: c) It passes through partially, causing blurred visibility
Sol: Translucent materials, like frosted glass, allow light to pass partially, making objects blurry

Q3. What is the term for the left-right reversal in a plane mirror image? (1 Mark)
a) Rectilinear propagation
b) Shadow formation
c) Lateral inversion
d) Reflection

Answer: c) Lateral inversion
Sol: Lateral inversion is the left-right reversal in a plane mirror image

Q4. Which device uses two mirrors to see objects not directly visible? (1 Mark)
a) Pinhole camera
b) Periscope
c) Kaleidoscope
d) Torch

Answer: b) Periscope
Sol: A periscope uses two mirrors to reflect light and see objects, like in submarines

Q5. Which material produces the darkest shadow? (1 Mark)
a) Glass
b) Tracing paper
c) Cardboard
d) Clear plastic

Answer: c) Cardboard
Sol: Opaque materials like cardboard block all light, creating the darkest shadows,

Q6. Give two differences between luminous and non-luminous objects. (2 Mark)

Sol:

Luminous Objects
1. Luminous objects produce their own light. 
2. Example: Sun, stars, fireflies.

Non Luminous Objects
1. Non-luminous objects do not produce light but reflect it from luminous objects. 
2. Example: Moon, mirrors.

Q7. Why is "AMBULANCE" written in reverse on the front of vehicles? (2 Mark)

Sol:"AMBULANCE" is written in reverse letters so that drivers ahead see it correctly in their rear-view mirrors due to lateral inversion. This helps them quickly recognize and make way for ambulances.

Q8. What makes LED lamps environmentally friendly? (2 Mark)

Sol: LED lamps use less electricity, making them energy-efficient and reducing environmental impact. They also last longer than traditional bulbs, saving resources.

Q9.  What are the characteristics of an image formed in a plane mirror? (3 Mark)

Sol: The plane mirror has following characteristics

• Same size as the object.

• Upright (erect).

• Laterally inverted (left appears as right and vice versa).

• The distance of the image from the mirror equals the distance of the object from the mirror.

Q10 What is a periscope, and mention its practical uses. (3 Mark)

Sol:

A simple periscope is made by placing two plane mirrors inside a Z-shaped box. 

The reflection from these mirrors allows us to see objects that are not directly visible. 

Practical uses of a periscope:

• Submarines use periscopes to see above water without surfacing.

• Soldiers use periscopes to observe enemy movements safely from bunkers or trenches.

• Useful in crowds to see over taller individuals.

Q11. ​How do you form a shadow using a torch? (3 Mark)

Sol: To form a shadow, you need 
1. A light source (like a torch), 
2. An opaque object to block the light
3. A screen (like a wall or a cardboard). 
When the object blocks the light, the shadow forms on the screen in the shape of the object.

Q12: Describe the process of shadow formation. (5 Mark)

Sol: Shadows are formed when an object blocks the path of light. Since light travels in a straight line, when it hits an opaque object, the area behind the object will not receive light. This creates a shadow. The size, shape, and sharpness of the shadow depend on the position of the object, the light source, and the screen where the shadow is cast.

• Opaque objects create darker shadows because they block most or all of the light.

• Translucent objects create lighter shadows because some light passes through them.

• Even transparent objects, like clear plastic, can create faint shadows, as they only slightly allow light to pass through.

When you move the object closer to the light source, the shadow becomes larger. If you move the object further away, the shadow becomes smaller. The position of the object also affects the sharpness of the shadow—closer objects create sharp shadows, while distant objects create blurry ones.

Q13: Explain how the Moon reflects light. (5 Mark)

Sol: The Moon does not produce its own light. It is a non-luminous object, which means it doesn’t emit light. Instead, the Moon reflects the light of the Sun that falls on its surface. This reflected light is what we see as moonlight.

The Moon's surface is rough and uneven, so the light it reflects is scattered. This is why moonlight is not as bright as sunlight. During the day, we can’t see the moon's light because the sunlight is much brighter. But at night, when the Sun’s light is not in the sky, the moon’s reflection becomes visible to us.

This phenomenon of reflection is similar to how mirrors work. The only difference is that the Moon’s surface reflects light unevenly due to its craters and rough texture, which is why the moonlight we see is softer and more diffused than sunlight.