# NCERT Science Class 10 Chapter 10 Light Reflection and Refraction CBSE Board Sample Problems Short Answer

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## Question

Name the type of mirror used ¡n the following situations:

(b) Side/rear-view mirror of a vehicle.

(c) Solar furnace.

### Solution

(a) Headlights of a car- concave mirror to give parallel beam of light after reflection from concave mirror.

(b) Side/rear-view mirror of vehicle- convex mirror as it forms virtual erect and diminished image to give wider view field.

(C) Solar furnace- concave mirror to concentrate sunlight to produce heat in solar furnace.

## Question

A convex mirror used on a bus has a focal length of 200 cm. If a scooter ¡s located at 100 cm. from this mirror find the position, nature and magnification of the image formed in the mirror.

### Solution

Image is virtual.

## Question

An object is placed at a distance of 12 cm in front of a concave mirror. It forms a real image four times larger than the object. Calculate the distance of the image from the mirror

## Question

A coin placed at the bottom of a tank appears to be raised when water is poured into it.

Explain.

### Solution

• This occurs due to the, phenomenon of refraction of light. 1-lere, the ray of light from the coin travels from a denser medium to a rarer medium.

• In this process it bends away from the normal.

• The point from which the refracted rays appear to come gives the apparent position of the coin.

• As the rays appear to come from a point above the coin, so, the coin seems to be raised.

## Question

(1) Define real ¡mage of an object.

(2) Name the mirror that

(a) Can give real as well as virtual image of an object.

(b) Will always give virtual image of same size of an object.

(c) Will always give virtual and diminished image of an object.

(d) Is used by a doctor in examining teeth

### Solution

(1) Real image of an object is the image formed due to actual intersection of light rays coming from object through an optical device. It can always be taken on screen.

(2)

(a) Concave mirror

(b) Plane mirror

(c) Convex mirror

(d) Concave mirror

## Question

Find the position of the object of height 5 cm in front of a concave lens of focal length 20 cm to get the image at a distance of 15 cm from the lens. Also find the height and nature of image formed.

### Solution

Using we get

Since, we get

Image is diminished and virtual

## Question

Define the following terms in the context of spherical mirrors:

(i) Pole

(ii) Centre of curvature

(iii) Principal axis

(iv) Principal focus

### Solution

(i) Pole: The centre of the reflecting surface of the mirror is called pole.

(ii) Centre of curvature: The centre of the hollow sphere of which the reflecting surface of mirror forms a part is called centre of curvature.

(iii) Principal axis: The imaginary line passing through the pole and the centre of curvature of a spherical mirror is called principal axis.

(iv) Principal focus: When incident rays parallel to principal axis, after reflection, either converge to or appear to diverge from a fixed point on the principal axis called principal focus

## Question

What do you mean by the reflection of light?

### Solution

The bouncing back of light after striking a polished / smooth surface.

## Question

1. If the image formed by a lens formed for all positions of an object placed in front of it is always erect and diminished, what is the nature of this lens? Draw a ray diagram to justify your answer.

2. If the numerical value of power of this lens is 10 D, what is the focal length in the

Cartesian system?

### Solution

1. This is a concave lens.

2.

As D

So, focal length

## Question

Draw ray diagram to show formation of magnified (a) real and (b) virtual image of an object by a concave mirror.

## Question

A 5 cm tall object is placed on the principal axis of convex lens of focal length 50 cm at a distance of 40 cm from it. Find the nature, position and size of the image.

### Solution

Using lens formula

Nature: virtual (negative sign shows that image is formed on the same side of lens as the object).

Now,

Height of image is +25 cm

Positive sign shows that image is erect

## Question

At what distance should an object be placed from a convex lens of focal length 18cm to obtain an image at 24cm from it on the other side? What will be the magnification produced in this case? Draw a ray diagram. (1+1+1)

Ray diagram