Extra Questions for Chapter 11 Light: Shadows and Reflections Class 7 Science Curiosity
Class 11 Light: Shadows and Reflections Extra Questions
Very Short Answer Questions
Question 1. What is a luminous object?
Answer
An object that emits its own light.
Question 2. Name a natural source of light.
Answer
The Sun.
Question 3. Name an artificial source of light.
Answer
Electric bulbs.
Question 4. Does the Moon produce its light?
Answer
No, the Moon reflects sunlight.
Question 5. How does light travel under normal conditions?
Answer
Light travels in a straight line.
Question 6. What is the characteristic path of light?
Answer
The path of light is always straight and never curved.
Question 7. What is the reflection of light?
Answer
When light bounces off a surface and changes direction.
Question 8. What is the direction of light travel called?
Answer
Rectilinear propagation.
Question 9. What happens when light passes through aligned holes in a straight line?
Answer
It creates a bright spot on a screen.
Question 10. What device uses two mirrors to see objects that are not directly visible?
Answer
A periscope.
Question 11. What is a transparent material?
Answer
A material that lets light pass through almost completely, like glass.
Question 12. What kind of material allows only some light to pass through?
Answer
Translucent material.
Question 13. Give one example of a translucent material.
Answer
Tracing paper.
Question 14. What is formed when an object blocks light?
Answer
A shadow.
Question 15. What type of image does a plane mirror form?
Answer
A virtual, upright, same-size, laterally inverted image.
Question 16. What are virtual images?
Answer
Virtual images are images that cannot be captured on a screen or surface.
Question 17. What is lateral inversion in a mirror image?
Answer
The left side appears as the right side and vice versa.
Question 19. What type of shadow do translucent objects create?
Answer
Lighter and less distinct shadows.
Short Answer Questions
Question 1. Why we are not able to see the candle flame through a bent pipe?
Answer
We cannot see the candle flame through a bent pipe due to the way light travels.
Here are the key points:
- Light travels in straight lines.
- A bent pipe alters the path of light, preventing it from reaching our eyes.
Thus, the flame is not visible when viewed through the bent pipe.
Question 2. What happens when light falls on a mirror?
Answer
A mirror changes the direction of light that hits it. This process is known as the reflection of light.
- When light strikes a mirror, it bounces back.
- This change in direction allows us to see our reflection.
- Mirrors can be made from various shiny surfaces, including polished metals and glass.
Question 3. Why do opaque objects create shadows?
Answer
Opaque objects block the path of light, and as a result, a dark area forms on the opposite side of the object. This dark area is the shadow. Since opaque objects completely block light, they create the darkest shadows.
Question 4. What happens when light passes through transparent materials?
Answer
When light passes through transparent materials, like glass or clear water, it passes almost completely through them, allowing us to see through the material clearly. Transparent materials allow most of the light to pass through without scattering.
Question 5. What is the difference between luminous and non-luminous objects?
Answer
Luminous objects are those that emit their own light, such as the Sun, stars, and fireflies. Non-luminous objects do not emit light; they reflect light from luminous objects. The Moon is an example of a non-luminous object because it only reflects sunlight.
Question 6. What happens when light is reflected by a mirror?
Answer
When light strikes a mirror, it changes direction and is reflected. The angle at which light hits the mirror (angle of incidence) is equal to the angle at which it is reflected (angle of reflection). This is known as the law of reflection.
Question 7. How does the Moon produce light?
Answer
The Moon does not produce its own light. It is a non-luminous object that reflects the light of the Sun. This reflected light is what we see as moonlight. The surface of the Moon reflects sunlight, but because the surface is rough, the light is scattered.
Question 8. What are real images, and where are they captured?
Answer
Real images are images that can be captured on a screen or surface. For example, in a camera, images are real and can be captured on the negative.
Question 9. How does a periscope work?
Answer
A periscope allows you to see objects that are out of your direct line of sight by using two mirrors placed at 45° angles inside a box. Light entering the periscope is reflected off both mirrors, allowing you to see over obstacles or around corners.
Question 10. What types of spherical mirrors exist, and how do they differ?
Answer
There are two types of spherical mirrors: concave mirrors and convex mirrors. Concave mirrors have a curved inward reflecting surface, while convex mirrors have a curved outward reflecting surface.
Question 11. Differentiate between concave and convex mirrors and provide examples of their applications.
Answer
Concave mirrors are used to magnify objects and can form both virtual and real images. They are used in applications such as dental mirrors, flashlights, and car headlights. Convex mirrors, on the other hand, form virtual, erect, and diminished images. They are used in rear-view mirrors in vehicles, parking lots, and security applications.
Question 12. What happens when light falls on a polished or a shiny surface?
Answer
When light strikes a polished or shiny surface, it is primarily reflected. This reflection occurs due to the smoothness of the surface, which allows light to bounce back in a consistent direction.
- The light does not scatter but reflects at the same angle it hits the surface.
- Common examples of such surfaces include mirrors, stainless steel, and calm water.
- This property is what makes these surfaces appear shiny and allows us to see reflections.
Question 13. How can we change the path of light?
Answer
We can change the path of light by using any shiny or polished surface. Here are some examples:
- A stainless steel plate can redirect light.
- A steel spoon acts like a mirror.
- The surface of water can also reflect light.
In essence, any shiny surface can alter the direction of light.
Question 14.What is the role of mirrors in forming images?
Answer
Mirrors form images by reflecting light. The image formed in a plane mirror is virtual, meaning it cannot be captured on a screen. The image is always upright, of the same size as the object, and laterally inverted (left-right reversal).
Question 15. What is the purpose of red oxide coating on transparent spherical surfaces?
Answer
Red oxide coating helps tell concave and convex mirrors apart. If the concave side is silvered, it’s a concave mirror; if the convex side is silvered, it’s a convex mirror. The coating just marks the non-reflecting side and doesn’t change how the mirror works.
Question 16. Describe the dispersion of light through a prism and what causes it.
Answer
Dispersion of light through a prism occurs when a narrow beam of sunlight passes through a prism. Different component colours of white light bend differently as they pass through the prism due to the phenomenon of refraction, creating a spectrum of colours.
Question 17. "What is meant by the angle of incidence and angle of reflection, and how are they related?
Answer
The angle of incidence is the angle between the incoming light ray and the normal, and the angle of reflection is the angle between the reflected ray and the normal. They are equal, as per the law of reflection.
Question 18. What is a rainbow, and how is it formed?
Answer
A rainbow is a band of colours extending from violet to red, formed by the refraction and reflection of the sun's rays through raindrops. It appears when it is raining in one part of the sky and sunny in another. The center of the rainbow's arc is always directed away from the sun.
Question 19. Describe the applications of lenses and provide examples.
Answer
Lenses have various applications, such as magnifying glasses for reading, cameras for photography, microscopes for scientific observation, and telescopes for stargazing. They are also used in devices like binoculars and projectors.
Question 20. Why does changing the colour of an object not affect the colour of its shadow?
Answer
Shadows are formed because the object blocks light from reaching a surface. Since a shadow is simply an area with less or no light, it appears dark or black regardless of the object's colour. The colour of the object does not add light to the shadow, so the shadow colour remains unaffected.
Question 21. Give two differences between luminous and non-luminous objects.
Answer
|
Luminous Objects |
Non Luminous Objects |
|
1. Luminous objects produce their own light. |
1. Non-luminous objects do not produce light but reflect it from luminous objects. |
|
2. Example: Sun, stars, fireflies. |
2. Example: Moon, mirrors. |
Question 22. Why is "AMBULANCE" written in reverse on the front of vehicles?
Answer
"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.
Question 23. Why is it important to recycle LED lamps properly? What could happen if they end up in regular waste?
Answer
LED lamps contain small amounts of metals and electronic parts that can be harmful to the environment if thrown away carelessly. Recycling them properly ensures these materials are safely processed and reused, preventing pollution. If LED lamps go into regular trash, toxic substances can leak into soil and water, harming plants, animals, and people.
Question 24. Given that light generally travels in a straight line, how do you explain the bending of light in phenomena like rainbows or when light passes through water?
Answer
Although light usually travels straight, it bends when it passes from one material to another at an angle — this is called refraction. For example, when sunlight passes through raindrops, it bends inside the drops and splits into different colours, creating a rainbow. Similarly, light bends when it moves from air into water because water is denser, changing the light’s speed and direction.
Question 25. Imagine you are asked to create a new educational toy using the properties of light and reflection. What would it be and how would it work?
Answer
I would create a “Light Maze” toy. It would have a small laser pointer at one end and a maze made of mirrors inside a box. Children would move mirrors to reflect the laser light through the maze and hit a target. This would teach them how light travels straight and reflects off surfaces at equal angles, making learning fun and interactive.
Question 26. Why does the size and shape of a shadow change when you move the light source closer or farther from the object?
Answer
When the light source moves closer to the object, the rays spread out more, and the shadow becomes bigger and less sharp because the light is coming from a wider angle. When the light source is farther away, the rays are more parallel and the shadow becomes smaller and sharper. Also, changing the angle of the light source changes the shape of the shadow because the light hits the object differently.
Long Question Answer
Question 1. What is reflection of light?
The reflection of light occurs when a light ray bounces back after hitting a surface.
Key points include:
- Light travels in straight lines.
- When light strikes a smooth surface, it changes direction.
- This change in direction is known as reflection.
- Common reflective surfaces include mirrors and calm water.
Question 2. What is a periscope, and mention its practical uses.
Answer
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.
Question 3. Explain how light travels and what happens when it hits different objects.
Answer
Light travels in a straight line. This is known as the rectilinear propagation of light.
When light strikes different materials, it behaves in different ways:
- Transparent materials, like glass and clear water, allow light to pass through them completely. This means we can see through them clearly.
- Translucent materials, like tracing paper or frosted glass, let some light pass through but not all. They cause the light to scatter, so objects on the other side are not clearly visible.
- Opaque materials, like cardboard or wood, block light completely. No light passes through opaque objects, which is why we can't see through them.
In experiments, when you place objects in the path of a torch beam, you can observe that light passes through transparent materials but either partially or completely blocks through translucent and opaque materials.
Question 4. How do mirrors reflect light?
Answer
Mirrors reflect light by changing the direction of the light that falls on them. When light hits a mirror, it bounces off the surface. This reflection allows us to see an image of objects placed in front of the mirror. The reflection follows a law called the law of reflection, which states that the angle at which the light hits the mirror (angle of incidence) is equal to the angle at which it reflects off (angle of reflection).
In experiments with mirrors:
- If you direct light onto a flat, shiny surface (like a mirror), it will reflect in a straight line to another surface or wall.
- If the mirror is tilted, the direction of the reflected light will change, but the angle of incidence will always equal the angle of reflection.
The images formed in a plane mirror are:
- Erect (not upside down),
- Same size as the object,
- Laterally inverted (left and right are reversed),
- Cannot be projected on a screen because they are virtual.
Question 5. Design a simple experiment at home to demonstrate that light travels in a straight line. Describe the steps.
Answer
You can try this easy experiment: Take three pieces of cardboard and make a small hole in each. Now, hold these three cardboard pieces so that the holes are perfectly lined up in a straight line.
- Shine a torch or flashlight through the holes.
- You will see the light pass through all three holes and form a bright spot on a wall behind.
- Now, move one cardboard piece slightly so that the holes are no longer aligned.
- The light spot disappears, showing that light cannot bend around the hole.
This proves that light travels in a straight line.
Question 6. How can we create a periscope and how does it work?
Answer
A periscope is a simple device that allows you to see things that are hidden from direct view. It works by using two mirrors arranged at an angle to each other. Here's how to make a simple periscope:
- Take a rectangular box and cut two holes on opposite sides.
- Place two plane mirrors inside the box at an angle of 45° to each other.
- Through one hole, you can look into the periscope, and through the other hole, you can see the image reflected by the mirrors.
When light enters through the first hole, it strikes the first mirror and is reflected onto the second mirror. The second mirror then reflects the light to the second hole, allowing you to see objects that are outside the direct line of sight.
Periscopes are often used in submarines, tanks, or by soldiers to observe the surroundings without exposing themselves. They are useful for seeing over obstacles or around corners.
Question 7. Explain how the Moon reflects light.
Answer
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.
Question 8. Assume, a person is standing in front of a plane mirror. The distance between the mirror and his image is 6 m. If the person moves 2 m towards the plane mirror, what would be the distance between the person and his image?
Answer
Since, the image is 6m away from the plane mirror. So, it means that the object is also 6m away from the mirror.
[Because OP = PI]
So, when the person moves 2 m towards the plane mirror, then the distance between the person and the plane mirror will be equal to (6 m – 2 m) = 4 m, this means that distance between the image and the mirror will be 4m.
The distance between the person and his image = PO’+ PI’= 4 + 4 = 8m
Question 9. It was observed that when the distance between an object and a lens decreases, the size of the image increases. What is the nature of this lens? If you keep on decreasing the distance between the object and the lens, will you still able to obtain the image on the screen? Explain.
Answer
The lens in question is a convex lens. When the distance between an object and a convex lens decreases, the size of the image increases. This is because a convex lens converges light rays, creating a larger image as the object gets closer. As you continue to decrease the distance between the object and the lens:
- The image will initially remain clear and magnified.
- Eventually, the image may become virtual, meaning it cannot be projected onto a screen.
At very close distances, the image may appear distorted or blurred.