# Light - Reflection and Refraction

### It is desired to obtain an erect image of an object

It is desired to obtain an erect image of an object, using concave mirror of focal length of 12 cm.

1. What should be the range of the object distance in the above case?
2. Will the image be smaller or larger than the object? Draw a ray diagram to show the formation of image in this case.
3. Where will the image of this object be, if it is placed 24 cm in front of the mirror?

### A lens produces a magnification of -0.5. Is this a converging or diverging lens?

A lens produces a magnification of -0.5. Is this a converging or diverging lens? If the focal length of the lens is 6 cm, draw a ray diagram showing the image formation in this case.

### A girl was playing with a thin beam of light from a laser torch

A girl was playing with a thin beam of light from a laser torch by directing it from different directions on a convex lens held vertically. She was surprised to see that in a particular direction, the beam of light continues to move along the same direction after passing through the lens. State the reason for her observation. Draw a ray diagram to support your answer.

### On entering in a medium from air, the speed of light becomes half

On entering in a medium from air, the speed of light becomes half of its value in air. Find the refractive index of that medium with respect to air?

### A glass slab made of a material of refractive index n1

A glass slab made of a material of refractive index n1 is kept in a medium of refractive index n2. A light ray is incident on the slab. Draw the path of the rays of light emerging from the glass slab, if (i) n1 > n2 (ii) n1 = n2 (iii) n1 < n2

### The absolute refractive index of Ruby is 1.7

The absolute refractive index of Ruby is 1.7. Find the speed of light in Ruby. The speed of light in vacuum is 3 × 108 m/s.

### A 10 cm tall object is placed perpendicular to the principal axis

A 10 cm tall object is placed perpendicular to the principal axis of a convex lens of focal length 12 cm. The distance of the object from the lens is 18 cm. Find the nature, position and size of the image formed.

### An object is kept 40 cm in front of a concave mirror of focal length 20 cm

An object is kept 40 cm in front of a concave mirror of focal length 20 cm. Find the position and nature of the image. Draw a ray diagram to show the formation of image in this case.

### An object of height 1.2 m is placed before a concave mirror

An object of height 1.2 m is placed before a concave mirror of focal length 20 cm so that a real image is formed at a distance of 60 cm from it. Find the position of an object. What will be the height of the image formed?

### Rohit focused the image of a candle flame on a white screen

Rohit focused the image of a candle flame on a white screen using a convex lens. He noted down the position of the candle, screen and lens as under:
Position of candle = 26.0 cm
Position of convex lens = 50.0 cm
Position of screen = 74.0 cm
i) What is the focal length of the convex lens?
ii) Where will the image be formed if he shifts the candle towards the lens at a position of 38 cm?
iii) Draw a ray diagram to show the formation of the image in case (ii) as said above?

### We wish to obtain an equal sized inverted image of a candle flame on a screen

We wish to obtain an equal sized inverted image of a candle flame on a screen kept at distance of 4 m from the candle flame.

1. Name the type of lens that should be used.
2. What should be the focal length of the lens and at what distance from the candle flame the lens be placed.
3. Draw a labelled diagram to show the image formation in this case.

### A 5 cm tall object is placed at a distance of 30 cm from a convex mirror

A 5 cm tall object is placed at a distance of 30 cm from a convex mirror of focal length 15 cm. Find the position, size and nature of the image formed.

### If the image formed by a spherical mirror for all positions

If the image formed by a spherical mirror for all positions of the object placed in front of it is always erect and diminished, what type of mirror is it? Draw a labelled ray diagram to support your answer.

### What is meant by power of a lens

What is meant by power of a lens? Write its SI unit. A student uses a lens of focal length 40 cm and another of –20 cm. Write the nature and power of each lens.

### State the laws of refraction of light

State the laws of refraction of light. Explain the term 'absolute refractive index of a medium' and write an expression to relate it with the speed of light in vacuum.