Reflection of Light | Class 8 | Science | Chapter 16 | Maharashtra State Board
Explore the fascinating concepts of light reflection, including laws of reflection, types of reflection, and practical experiments like periscopes and kaleidoscopes. Learn how light interacts with surfaces through engaging activities and solved examples.
Questions & Answers
1. Fill in the blanks:
i. The perpendicular to the mirror at the point of incidence is called …………. .
Ans.
The perpendicular to the mirror at the point of incidence is called the normal.
ii. The reflection of light from a wooden surface is ……….. reflection.
Ans.
The reflection of light from a wooden surface is irregular reflection.
iii. The working of a kaleidoscope is based on the properties of …………… .
Ans.
The working of a kaleidoscope is based on the properties of reflection of light.
2. Draw a figure describing the following:
The reflecting surfaces of two mirrors make an angle of 90° with each other. If a ray incident on one mirror has an angle of incidence of 30°, i draw the ray reflected from the second mirror. What will be its angle of reflection?
Ans.
For the ray C, the angle of reflection = 60°.
3. How will you explain the statement ‘We cannot see the objects in a dark room’?
Ans.
In a room that is completely dark, no light falls on objects. Hence, no light enters our eyes. Hence, there is no sensation of vision, i.e., we cannot see the objects.
4. Explain the difference between regular and irregular reflection of light.
Ans.
For regular reflection of light, the angles of incidence as well as the angles of reflection are the same for all parallel rays of light incident on the plane and smooth surface. Hence, the reflected rays are also parallel to one another.
For irregular reflection of light, the angles of incidence for parallel rays of light incident on the rough surface are not equal, and hence the angles of reflection are also not equal. Here, the reflected rays are not parallel to one another and spread over a large surface.
5. Draw a figure showing the following:
(a) Incident ray, (b) Normal, (c) Angle of incidence, (d) Angle of reflection, (e) Point of incidence, (f) Reflected ray.
Ans.
6. Study the following incident.
Swara and Yash were looking in a water-filled vessel. They could see their images clearly in the still water. At that instant, Yash threw a stone in the water. Now their images were blurred. Swara could not understand the reason for the blurring of the images. Explain the reason for blurring of the images to Swara by answering the following questions:
i. Is there a relation between the reflection of light and the blurring of the images?
Ans.
Yes.
ii. Which types of reflection of light can you notice from this?
Ans.
Regular reflection of light when light is incident on the still water and irregular reflection of light when light is incident on the water as ripples are produced on its surface when a stone is thrown in the water.Still water behaves as a plane and smooth surface while oscillating water behaves as a rough surface.
iii. Are the laws of reflection followed in these types of reflection?
Ans.
Yes.
7. Solve the following examples.
a. If the angle between the plane mirror and the incident ray is 40°, what are the angles of incidence and reflection?
Solution:
The angle between the plane mirror and the incident ray is 40°. Therefore, the angle of incidence (i) = the angle made by the incident ray with the normal to the plane mirror = 90° – 40° = 50°. The angle of reflection, r – i – 50°.
b. If the angle between the mirror and reflected ray is 23°, what is the angle of incidence of the incident ray?
Solution:
The angle between the mirror and the reflected ray is 23°.
Therefore, the angle of reflection (r) = the angle made by the reflected ray with the normal to the plane mirror = 90° – 23° = 67°.
∴ The angle of incidence, i = r = 67°.
E X T R A
1. Rewrite the following statements by selecting the correct option:
1. If the angle made by the incident ray with the surface of a plane mirror is 30°, the angle of reflection must be …….. .
(a) 30°
(b) 90°
(c) 60°
(d) 15°
Ans.
If the angle made by the incident ray with the surface of a plane mirror is 30°, the angle of reflection must be 60°.
2. If the angle of incidence is 40°, the angle made by the reflected ray with the surface of the plane mirror must be ……. .
(a) 40°
(b) 50°
(c) 20°
(d) 80°
Ans.
If the angle of incidence is 40°, the angle made by the reflected ray with the surface of the plane mirror must be 50°.
3. If the angle of incidence is 20°, the angle made by the reflected ray with the normal to the surface must be ……… .
(a) 20°
(b) 70°
(c) 10°
(d) 40°
Ans.
If the angle of incidence is 20°, the angle made by the reflected ray with the normal to the surface must be 20°.
4. In a kaleidoscope, the mirrors are inclined to each other at ……. .
(a) 60°
(b) 30°
(c) 45°
(d) 90°
Ans.
In a kaleidoscope, the mirrors are inclined to each other at 60°.
5. In a periscope, the mirrors are ………….. .
(a) parallel to each other
(b) at right angles to each other
(c) inclined at 45° to each other
(d) inclined at 60° to each other
Ans.
In a periscope, the mirrors are parallel to each other.
2. Find the odd one out and give the reason:
1. Plane mirror, Plywood, Wood, Rough tile.
Ans.
Plane mirror. In this case, regular reflection of light takes place. In other cases, reflection of light is irregular.
3. State whether the following statements are True or False.
(If a statement is false, correct it and rewrite it.)
1. The sense of vision is the most important among our five senses.
Ans.
True.
2. In a periscope, the angle between the incident ray and the normal to the mirror is 30°.
Ans.
False. (In a periscope, the angle between the incident ray and the normal to the mirror is 45°.)
4. Answer the following questions in one sentence each:
1. What is an incident ray? OR Define incident ray.
Ans.
A ray of light falling on a surface is called an incident ray.
2. What is the point of incidence? OR Define point of incidence.
Ans.
The point at which the incident ray strikes the surface is called the point of incidence.[Note: It is also the point of reflection.]
3. What is the normal? OR Define normal.
Ans.
The perpendicular to a surface at the point of incidence is called the normal.
4. What is the reflected ray? OR Define reflected ray.
Ans.
The ray of light that leaves the surface at the point of reflection (the same as the point of incidence) is called the reflected ray.
5. What is the angle of incidence? OR Define angle of incidence.
Ans.
The angle between the incident ray and the normal is called the angle of incidence.
6. What is the angle of reflection? OR Define angle of reflection.
Ans.
The angle between the reflected ray and the normal is called the angle of reflection.
5. Answer the following questions:
1. What is reflection of light?
Ans.
When light rays fall on an object, their direction changes and they turn back. This is called the reflection of light.
2. What is regular reflection of light?
Ans.
The reflection of light from a plane and smooth surface is called regular reflection of light.
3. What is irregular reflection of light?
Ans.
The reflection of light from a rough surface is called irregular reflection of light.
4. How do you see if the barber m a saloon has cut the hair on your neck properly or not?
Ans.
In a saloon, there are mirrors in your front and at back. The image of the back of your head is formed in the mirror at the back. The image of this image is formed in the mirror in front of you. Thus you can see how the hair at the backside of your head is cut.
5. What type of image do we see in a mirror? What happens to the left and right sides?
Ans.
The image in a plane mirror is upright (erect) and of the same size as the object, but the left and right sides are interchanged. Our right hand appears to be the left hand in the image and the left hand appears to be the right hand in the image. (This is called lateral inversion.)
6. How do we see the image of the moon in water?
Ans.
The moon is not self luminous. The sunlight falling on the surface of the moon is reflected. This reflected light is again reflected by water to give us the image of the moon.
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