Question 1

Question 1Describe an experiment to show that a light ray bends when it passes from one transparent medium into another transparent medium.

Accepted Answer

Experiment to show that a light ray bends when it passes from one transparent medium into another transparent medium.Take an empty beaker and a pencil. Place the pencil ABC obliquely in the beaker.Look at the pencil from side. It appears straight as shown in figure (a).Now pour water into the beaker up to its brim.Pencil appears to be bent as ABD at the surface of water as shown in the figure (b).The light ray coming from the tip C of the pencil bends at the surface of water as it enters in air and it appears to be coming from point D. Due to refraction of light from water to air, the pencil ABC appears as ABD.This shows that when a ray of light passes from one transparent medium into another transparent medium it bends.

Question 2

Question 3The diagram given below shows a ray of light AO falling on a surface separating two media. Draw the refracted ray in each, case.(a)(b)(c)

Accepted Answer

(a) When light ray AO passes from air (rarer medium) to water (denser medium), it bends towards the normal as shown below.(b) When light ray AO travels from water (denser medium) to air (rarer medium), it bends away from the normal as shown in the diagram below.(c) When light ray AO is incident normally to the surface, it passes undeviated as shown in the figure below.

Question 3

Question 5The diagram below shows a ray of light AO falling on a rectangular glass slab PQRS. Complete the diagram till the ray of light emerges out of the slab. Label on the diagram the incident ray, the refracted ray and the emergent ray.

Accepted Answer

The completed diagram showing the ray of light till it emerges out of the slab is given below :AO — incident rayOB — refracted rayBC — emergent ray

Question 4

Question 6What is a prism? Draw a ray diagram to show the refraction of a light ray through a prism.

Accepted Answer

A prism is a transparent medium bounded by five plane surfaces with a triangular cross section.In symbol form it is represented by the triangle ABC :The refraction of a light ray through a prism is shown below.The light ray PQ of a single colour is incident obliquely on the surface AB of the prism. As the ray PQ moves from air (rarer) to glass (denser), it bends towards normal and travels as refracted ray QR. The refracted ray QR at the face AC of the prism again undergoes refraction (bends away from the normal) as it moves from glass (denser) to air (rarer) and emerges out as ray RS (emergent ray) from the prism.

Question 5

Question 7A ray of white light falls on a prism. Draw a ray diagram to show that the prism disperses the white light.

Accepted Answer

Dispersion of a white light into its constituent colours by a prism is shown in the below figure.

Question 6

Question 8In below figure, AO is the ray of white light falling on a prism PQR. Complete the diagram till the light emerges out from the prism and falls on the screen.

Accepted Answer

White light splits up into seven constituent colours after passing through a prism. These seven colours VIBGYOR arranged from bottom to top are seen on the screen.

Question 7

Question 9State the two kinds of spherical mirrors and distinguish them with the aid of proper diagrams.

Accepted Answer

The two kinds of spherical mirrors are:Concave mirrorConvex mirrorSl.No.Concave mirrorConvex mirror1.It is made by silvering the outer surface of the hollow sphere.It is made by silvering the inner surface of the hollow sphere.2.The reflection takes place from the inner concave surface.The reflection takes place from the outer bulged surface.Figure of concave and convex mirror is shown below:

Question 8

Question 10Explain the following terms:(a) Pole(b) Centre of curvature(c) Radius of curvature(d) Principal axisShow them on separate diagrams for each of the concave and convex mirrors.

Accepted Answer

(a) Pole — The geometric centre of the spherical surface of the mirror is called the pole of the mirror. It is represented by the symbol P.(b) Centre of curvature — The centre of curvature of a mirror is the centre of the sphere of which the mirror is a part. It is represented by the symbol C.(c) Radius of curvature — The radius of curvature of a mirror is the radius of the sphere of which the mirror is a part. It is represented by symbol R.(d) Principal axis — It is a straight line joining the pole of the mirror to its centre of curvature.

Question 9

Question 11What do you understand by the focus and focal length of a spherical mirror? Show them on separate diagrams for each of a concave mirror and a convex mirror.

Accepted Answer

The focus (F) of a concave mirror is a point on the principal axis at which the light rays incident parallel to the principal axis, meet (converge) after reflection from the mirror.The focus (F) of a convex mirror is a point on the principal axis at which the light rays incident parallel to the principal axis, appear to meet after reflection from the mirror.The distance of the focus from the pole of the mirror is called the focal length of the mirror.

Question 10

Question 12Draw suitable diagrams to illustrate how a beam of light incident parallel to the principal axis is reflected by:(a) a concave mirror and(b) a convex mirror.

Accepted Answer

(a) A beam of light incident parallel to the principal axis of a concave mirror, after reflection meets at a point called focus of the mirror.(b) A beam of light incident parallel to the principal axis of a convex mirror, after reflection appears to meet at a point called focus of the convex mirror.

Question 11

Question 13The diagrams given below show two parallel rays 1 and 2 incident on:(a) a concave mirror,(b) a convex mirror.Draw the reflected rays and mark the focus by the symbol F.

Accepted Answer

The completed diagrams with focus marked are shown below :C — Centre of curvature,F — Focus,P — Pole

Question 12

Question 14Complete the following diagrams given below by drawing the reflected rays for the incident rays 1 and 2 if F is the focus and C is the centre of curvature.

Accepted Answer

Ray 1 passing through the focus of a concave mirror gets reflected parallel to the principal axis.Ray 2 passing through the centre of curvature of a concave mirror is reflected along its own path.Ray 1 appearing to pass through the focus of a convex mirror gets reflected parallel to the principal axis.Ray 2 directed in the direction of centre of curvature of a convex mirror is reflected along its own path.

Question 13

Question 15Which are the two convenient rays that are chosen to construct the image formed by a spherical mirror for a given object? Explain with the help of suitable ray diagrams.

Accepted Answer

The two convenient rays that are chosen to construct the image formed by a spherical mirror for a given object are:A ray that passes through the center of curvature — A line joining the centre of curvature to any point on the surface of mirror is normal to the mirror at that point, therefore a ray AD passing through the center of curvature C (or appearing to pass through through the centre of curvature C) is incident normally on the spherical mirror.Since it's angle of incidence is zero, therefore the angle of reflection will also be zero and the ray AD gets reflected along it's own path DA as shown below:A ray parallel to the principal axis — A ray of light AD incident parallel to the principal axis, after reflection passes either through the focus F(in a concave mirror) or will appear to come from the focus F (in a convex mirror) along DB as shown below:

Question 14

Question 18Draw a ray diagram to show the formation of image of an object placed between the focus and centre of curvature of a concave mirror. State the position, size and nature of the image.

Accepted Answer

Nature — Image is real and inverted.Position — The image is formed beyond centre of curvature of the mirror.Size — The size of image is bigger than that of object.

Question 15

Question 19Draw a ray diagram to show the formation of image of an object placed between the pole and focus of a concave mirror. State the position, size and nature of the image.

Accepted Answer

Nature — The image is virtual and erect.Position — The image is formed behind the mirror.Size — The size of image is bigger than that of object.

Question 16

Question 20Draw a ray diagram to show the formation of the image of an object placed on the principal axis of a convex mirror. State the position, size and nature of the image. What happens to the image as the object is moved away from the mirror?

Accepted Answer

Nature — Image is virtual and erect.Position — The image is formed behind the mirror between focus and pole of the convex mirror.Size — Image is diminished in size.As the object is moved away from the mirror, the image moves towards the focus and the size decreases to a point.

Question 17

Question 21Draw separate diagrams for the formation of virtual image of an object by(a) a concave mirror and(b) a convex mirror.State the difference of the two images.

Accepted Answer

(a) When an object is placed between the pole and focus of a concave mirror, the image is formed behind the mirror. A virtual, erect and enlarged image of the object is formed.(b) In convex mirror for the object placed at finite distance, the image formed is always virtual, erect, diminished and it is formed between pole and focus of the mirror.Sl.No.Virtual Image ofConcave mirrorVirtual Image ofConvex mirror1.Image is enlarged.Image is diminished and if the object is at infinity then image is diminished to a point.2.Image is formed behind the mirror between the pole and focus.Image is formed between pole and focus. But if the object is at infinity then image is formed at the focus of the mirror.

Question 18

Question 22How can a concave mirror be used to obtain a virtual image of an object? Draw a diagram to illustrate your answer.

Accepted Answer

The object should be placed between the pole and focus of the concave mirror to obtain a virtual image of the object.

Question 19

Question 23A driver uses a convex mirror as a rear view mirror. Explain the reason with the help of a ray diagram.

Accepted Answer

A convex mirror diverges the incident light rays and always form a small, erect image between its pole and focus. This enables the driver to use it as a rear view mirror so that he could able to see all the traffic behind him approaching the mirror. It has wider field of view than a plane mirror.

Question 20

Question 16State the direction of incident ray which after reflection from a spherical mirror gets reflected along its own path. Give a reason.

Accepted Answer

A ray passing through the centre of curvature of a spherical mirror is reflected along its own path.A line joining the centre of curvature to any point on the surface of mirror is always normal to it. Thus, a ray passing through the centre of curvature is incident normally on the spherical mirror. Its angle of incidence is zero, therefore, the angle of reflection is also zero. It means that the ray gets reflected along its own path.

Light Energy

Exercise 5 Long Answer Type Questions

Exercise 5 Short Answer Type Questions

Exercise 5 Think And Answer