RBSE Solutions Class 7 Science Chapter 11 Light Shadows and Reflections

Light Shadows And Reflections Class 7 Question Answer

RBSE Class 7 Science Chapter 11 Light Shadows And Reflections Question Answer

Class 7 Science Curiosity Chapter 11 Question Answer (Exercise)

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Question 1. Which of the following are luminous objects? Mars, Moon, Pole Star, Sun, Venus, Mirror.
Answer: The Sun and the Pole Star are luminous objects. They create and give off their own light. All other objects listed, like Mars, the Moon, Venus, and a mirror, only shine because they reflect light from other sources, such as the Sun. Being able to produce its own light is a key characteristic of a luminous object.
In simple words: The Sun and the Pole Star make their own light. Other objects just reflect light from the Sun.

🎯 Exam Tip: Remember that luminous objects *produce* light, while non-luminous objects *reflect* light.

Question 2. Match the following columns:
Answer:

🎯 Exam Tip: Understand the basic properties of light and objects (transparent, opaque) to easily match them with their effects.

Question 3. Sahil, Rekha, Patrick and Qasima are trying to observe the candle flame through the pipe as shown in Fig. 11.16. Who can see the flame?
Answer: Only Patrick can see the candle flame. This is because light travels in a straight line. Sahil, Rekha, and Qasima are trying to look through bent pipes, which blocks the straight path of light. Patrick's pipe is straight, allowing the light from the candle flame to reach his eyes directly.
In simple words: Only Patrick can see the candle flame. Light always travels in a straight path, so you need a straight pipe to see it.

🎯 Exam Tip: Remember the fundamental principle that light travels in a straight line. This is crucial for understanding how we see objects and how shadows are formed.

Question 4. Look at the images shown in Fig. 11.17 and select the correct image showing the shadow formation of the boy.
Answer: Image (D) correctly shows how the boy's shadow is formed. The shadow is shortest when the sun is directly overhead. When the sun is to the right or left of an object, the shadow will appear on the opposite side of the object. This is because the sun's position affects both the length and direction of a shadow.
In simple words: When the sun is high above, shadows are small. When the sun is to one side, the shadow appears on the other side. Image (D) shows this correctly.

🎯 Exam Tip: The length and direction of a shadow change throughout the day, depending on the sun's position relative to the object.

Question 5. The shadow of a ball formed on a wall by placing the ball in front of a fixed torch as shown in Fig. 11.18. In scenario (i) the ball is closer to the torch, while in scenario (ii) the ball is closer to the wall. Choose the most accurate representation of the shadows formed in both scenaries from the
Answer: If the ball is placed closer to the torch, the shadow formed on the wall will be large and a bit blurry. This is correctly shown by scenario (ii). However, if the ball is positioned closer to the wall, the shadow on the wall will be smaller and have clearer edges. This is represented by scenario (i). The distance between the light source, object, and screen (wall) affects the shadow's size and sharpness.
In simple words: When the ball is near the torch, the shadow is big and blurry (like in scenario ii). When the ball is near the wall, the shadow is small and sharp (like in scenario i).

🎯 Exam Tip: Remember that the size and sharpness of a shadow depend on the distances between the light source, the object casting the shadow, and the surface where the shadow appears.

Question 6. Match the following columns based on how light affects shadows:
Answer:

🎯 Exam Tip: This exercise helps understand how light travels in straight lines and how the distance between light sources, objects, and screens affects shadows. When two light sources are used, each source can create its own shadow.

Question 8. Write your name on a piece of paper and hold it in front of a plane mirror such that the paper is parallel to the mirror. Sketch the image. What difference do you notice? Explain the reason for the difference.
Answer: When you hold your name in front of a plane mirror, the image of your name will appear laterally inverted. This means the left side of your name in real life will look like the right side in the mirror, and vice versa. However, the size and height of your name will stay the same. This happens because light rays bounce off the mirror at the same angle they hit it, causing a left-right reversal, which is a key property of reflection in plane mirrors.
In simple words: In a mirror, your name looks flipped from left to right, but its size stays the same. This is called lateral inversion and happens because of how light reflects.

🎯 Exam Tip: Lateral inversion is a common characteristic of images formed by plane mirrors, where the image is flipped horizontally but not vertically.

Question 9. Measure the length of your shadow at 9 AM, 12 PM and 4 PM with the help of your friend. Write down your observations:
(i) At which of the given times is your shadow the shortest?
(ii) Why do you think this happen?
Answer:
(i) The shadow is shortest at 12 PM (noon).
(ii) This occurs because at noon, the Sun is directly overhead. This causes the Sun's rays to hit the object almost straight down, making the shadow very short and directly beneath the object. In contrast, during the morning (9 AM) and evening (4 PM), the Sun is lower in the sky, so its rays hit the object at a slant. This slanted light causes longer shadows to be formed.
In simple words: (i) Your shadow is shortest at 12 PM. (ii) The shadow is shortest at noon because the sun is right above you, making the light hit straight down. In the morning and evening, the sun is lower, so shadows are longer.

🎯 Exam Tip: The angle at which sunlight hits an object determines the length of its shadow. A higher sun means a shorter shadow, and a lower sun means a longer shadow.

Question 11. Suppose you are given a tube of the shape shown in the figure 11.20 and two plane mirrors smaller than the diameter of the tube. Can this tube be used to make a periscope? If yes, mark where you will fix the plane mirrors.
Answer: Yes, this shaped tube can be used to construct a periscope. To do this, two plane mirrors should be placed at each open end of the tube. Each mirror must be angled at 45 degrees to the main axis of the tube. This specific angle ensures that light rays entering the first mirror are reflected downwards to the second mirror, which then reflects them into the viewer's eye, allowing us to see objects that are not in a direct line of sight.
In simple words: Yes, you can make a periscope with this tube. Put two flat mirrors inside, one at each end, tilted at a 45-degree angle. This helps light bounce from one mirror to the other so you can see around corners.

🎯 Exam Tip: Periscopes work on the principle of reflection, using two plane mirrors placed at 45-degree angles to change the direction of light.

Question 12. We do not see the shadow on the ground of a bird flying high in the sky. However the shadow is seen on the ground when the bird swoops near the ground. Think and explain why it is so.
Answer: When a bird flies very high in the sky, we usually don't see its shadow on the ground. This is because the great distance allows the light from the bird to scatter widely, making the shadow too faint and spread out to be noticeable. However, when the bird flies closer to the ground, the light does not have as much space to scatter, so the shadow is more concentrated and visible. The closer an object is to the surface where its shadow is cast, the clearer and more defined the shadow appears.
In simple words: Birds flying high don't make shadows we can see because their light scatters too much. When they fly low, the shadow is clear because the light doesn't spread out as much.

🎯 Exam Tip: The visibility and sharpness of a shadow depend greatly on the distance between the object casting the shadow and the screen (or ground) on which it is formed.

Question 1. What happens when an object comes in the path of light?
Answer: When an object comes into the path of light, what happens next depends on the type of object. If the object is transparent, like clear glass, light will pass straight through it entirely. If it's translucent, like frosted glass, light will pass through only partially, scattering a bit. But if the object is opaque, like a thick wall, it will block all the light, creating a shadow behind it.
In simple words: It depends on the object. Clear objects let all light through. Cloudy objects let some light through. Solid objects block all light, making a shadow.

🎯 Exam Tip: Objects are classified as transparent, translucent, or opaque based on how much light they allow to pass through them.

Question 2. What happens when an opaque object blocks the path of light?
Answer: When an opaque object blocks the path of light, it stops the light from passing through. This creates a dark area on the surface behind the object, which we call a shadow. Shadows are formed because opaque objects do not allow light to pass through them.
In simple words: When a solid object stops light, a dark spot appears behind it. This dark spot is called a shadow.

🎯 Exam Tip: Shadows are formed when an opaque object completely obstructs the path of light, preventing light from reaching a surface directly.

Question 3. When the opaque object was a shiny object like a polished steel plate, I got a shadow on the screen, but I also saw that there was a bright spot of light on the wall on the opposite side. Why was it so?
Answer: When a shiny, opaque object like a polished steel plate is in the path of light, it forms a shadow because it blocks light. However, the bright spot seen on the opposite wall is caused by the reflection of light. Shiny surfaces, like mirrors or polished metal, bounce light off their surface instead of absorbing it, changing the direction of the light rays.
In simple words: A shiny object makes a shadow because it blocks light. The bright spot on the other wall is from the light bouncing off the shiny object. This bouncing is called reflection.

🎯 Exam Tip: Reflection occurs when light bounces off a surface, and shiny, smooth surfaces are particularly good at reflecting light in a focused way.

Question 4. In a mirror, I can also see my face. Is that also due to the reflection of light?
Answer: Yes, when you see your face in a mirror, it is indeed due to the reflection of light. Mirrors have very smooth and shiny surfaces that efficiently bounce light rays back. The light from your face travels to the mirror, reflects off its surface, and then travels to your eyes, allowing you to see your own image.
In simple words: Yes, seeing your face in a mirror happens because of light reflecting. Light from your face hits the mirror and bounces back to your eyes.

🎯 Exam Tip: Mirrors work by reflecting light, which is why we can see images of ourselves and other objects in them. The smoother the surface, the clearer the reflection.