MSBSHSE Class 8 Science Chapter 16 Reflection of Light

Q1. Fill in the blanks

i. The perpendicular to the mirror at the point of incidence is called …………

ii. The reflection of light from a wooden surface is ………….. reflection.

iii. The working of Kaleidoscope is based on the properties of …………..

Answer i: The perpendicular to the mirror at the point of incidence is called normal line.

Answer ii: The reflection of light from a wooden surface is diffused reflection.

Answer iii: The working of Kaleidoscope is based on the properties of reflection of light.

Q2. Draw a figure describing the following.

The reflecting surfaces of two mirrors make an angle of 90^o with each other. If a ray incident of one mirror has an angle of incidence of 30^o , draw the ray reflected from the second mirror. What will be its angle of reflection?

Answer:

Here, ray AB in the incident ray on the first mirror which makes an angle of 30^o .

Ray CD is the reflected ray from the second mirror.

So, its angle of reflection is 60^o with the normal.

Q3. How will you explain the statement ‘we cannot see the objects in a dark room’?

Answer: When we switch off the light at night, the objects in the room cannot be seen and they can be seen as before when the light is switched on again. Thus, we can see objects when the light coming from these objects enters our eyes. The light entering our eyes may be emitted by the object or may be reflected by that object.

Q4. Explain the difference between regular and irregular reflection of light.

Answer: The difference between regular and irregular reflection of light are:

Regular reflection of light	Irregular reflection of light
It occurs on smooth surfaces such as a plane mirror.	It occurs on rough surfaces such as a black board.
The reflected rays are parallel to each other.	The reflected rays are non-parallel to each other.
The reflected rays are in one direction.	The reflected rays are in different direction.

Q5. 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

Answer:

Q6. 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 question.

i. Is there a relation between the reflection of light and the blurring of the images?

ii. Which types of reflection of light can you notice from this?

iii. Are laws of reflection followed in these types of reflection?

Answer i: Yes, there is a relation between the reflection of light and the blurring of the images.

Answer ii: We observe irregular type of reflection. To know more about irregular reflection please visit and link https://byjus.com/physics/laws-of-reflection/

Answer iii: Yes, laws of reflection are followed in these types of reflection.

Q7. Solve the following examples.

a. If the angle between the plane mirror and the incident ray is 40^o , what are the angles of incidence and reflection? (Ans. 50^o )

b. If the angle between the mirror and reflected ray is 23^o , what is the angle of incidence of the incident ray? (Ans. 67^o )

Answer a: Given, the angle made by the light ray with mirror is 40^o .

Therefore,angle between incident and normal ray is (90°- 40°) = 50°

We know that,

Angle of incidence = Angle of reflection = 50°

So, light bends by 50 + 50 = 100°

Answer b: Given, angle between the mirror and reflected ray is 23^o

Angle of reflection = Angle made by the reflected ray with the normal to the plane mirror.

So, 90^o –23^o

= 67^o

Q8. Define Reflection of light?

Answer: When light rays fall on an object their direction changes and they turn back. This is called the reflection of light. The rays falling on any surface are called incident rays. The point at which an incident ray falls is called the point of incidence. The rays going away from the surface after reflection are called reflected rays. The direction of the reflected rays is decided by some rules which are called laws of reflection.

Q9. Write the laws of reflection?

Answer: There are three laws of reflection. These are as given below.

• The angle of reflection is equal to the angle of incidence.
• The incident ray, the reflected ray and the normal lie in the same plane.
• The incident ray and the reflected ray are on the opposite sides of the normal.

Q10. Define regular reflection of light.

Answer: The reflection of light from a plane and smooth surface is called regular reflection of light. For regular reflection, the angles of incidence as well as of reflection are the same for all parallel rays falling on the surface. Thus, the reflected rays are also parallel to one another.

Q11. Define irregular reflection of light.

Answer: Reflection of light from a rough surface is called irregular reflection of light. In irregular reflection, the angles of incidence for parallel rays of incidence are not equal and therefore, their angles of reflection are also not equal. Thus, the reflected rays are not parallel to one another and spread over a large surface.

Q12. What is periscope used for?

Answer: Periscope is used in submarines to see objects above the surface of water. It is also used to observe and keep a watch on the objects or persons on the ground from an underground bunker. Periscope uses the properties of reflection of light.

Q13. What is Reflection on a Plane Mirror?

Answer: When the light rays which get stroked on the flat mirror and get reflected back. According to laws of reflection, the angle of reflection is equal to the angle of incidence. The image is obtained behind the plane which is present in the mirror. This process of obtaining a mirror image which is virtual and erect is known as a reflection on a plane mirror.

Q14. What type of image do we see in a mirror? What happens to the left and right sides?

Answer: A plane mirror reflects a duplicate image of an object or thing which appears identical. The reflection formed by the mirror after reflection of an object from the mirror is called mirror image of that object.

An equality in which the left and the right are reversed means we get the right side image to the left side and left side image to the right side.

Q15. Write the characteristics of Image formed by Plane Mirror.

Answer: Following are the characteristics of image formed by plane mirror:

• The image obtained by the plane mirror is always erect and virtual.
• The image size and the size of the object, both are equal.
• The distance between the image obtained is same as the distance at which the object is placed.
• Laterally inverted images are obtained.

Q16. How do we see the image of the Moon in water?

Answer: As moon is not self luminous, the Sun light 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. In this way light can be reflected several times.

Q17. A ray of light is incident towards a plane mirror at an angle of 30° with the mirror surface. What will be the angle of reflection?

Answer: Since the angle of incidence is measured between the incident ray and the normal, so, here the angle of incidence is not 60°

According to Law of Reflection,

θ_i = θ_r

Hence,

Angle of Reflection = 60°

Q18. What is a Kaleidoscope?

Answer: A kaleidoscope is an optical instrument consisting of two or more reflecting surfaces. These surfaces are tilted towards each other at a certain angle to obtain symmetrical patterns when viewed from the other end. The tube with reflecting surfaces consists of coloured pieces of glass. By rotating the tube, symmetrical images are created.

Q19. What is a mirror and explain the terms related to it.

Answer: A mirror is defined as reflecting surface and can be explained by the law of reflection, which states that when a ray of light is made to fall on the reflecting surface, the reflected ray has its angle of reflection, incident ray and the reflected ray are normal to the surface at a point of incidence.

The terms related to mirror are:

• Incident ray: It is defined as a ray of light that hits the surface.
• Reflected ray: It is defined as the ray of light that is reflected back after hitting the surface.
• Normal ray: It is defined as the ray that is 90° to the surface or the ray which is perpendicular to the reflecting surface.
• Refracted ray: It is defined as the incident ray which passes through a second medium resulting in the change of direction.
• Angle of incidence: It is defined as the angle between the incident ray the normal at which the incidence occurs.
• Angle of reflection: It is defined as the angle between the reflected ray with respect to the normal at which the reflection occurs.
• Angle of refraction: It is defined as the angle between the refracted ray and the normal at which the refraction occurs.

Q20. Write the types of mirror?

Answer: Following are the types of mirrors that are most widely used:

Plane mirror: The images formed from a plane mirror are the reflected images in their normal proportions but reversed from left to right. These are the most widely used mirrors.

Convex mirror: These are the spherical mirrors that are curved outward and the image obtained is virtual, diminished and erect for a real object.

Concave mirrors: These are the spherical mirrors that are curved inward and the image obtained from these mirrors depend on the placement of the object.