Exemplar Problems Solution for Class 10 Science Light MCQ Part 1

# Light

## Exemplar Problems

### MCQ Part 1

Question 1: Which of the following can make a parallel beam of light when light from a point source is incident on it?

1. Concave mirror as well as convex lens
2. Convex mirror as well as concave lens
3. Two plane mirrors placed at 90° to each other
4. Concave mirror as well as concave lens

Answer: (a) Concave mirror as well as convex lens

Question 2: A 10 mm long awl pin is placed vertically in front of a concave mirror. A 5 mm long image of the awl pin is formed at 30 cm in front of the mirror. The focal length of this mirror is

1. – 30 cm
2. – 20 cm
3. – 40 cm
4. – 60 cm

Answer: (b) – 20 cm

Explanation: Given, height of object = 10 mm, height of image = 5 mm, image distance = -30 cm,

Magnification =(h’)/h

=5/(10)=1/2=0.5

Since, m=v/u

Or, 0.5=(-30text(cm))/u

Or, u=-(30)/(0.5)=-60 cm

Mirror formula 1/v+1/u=1/f

Or, -1/(60)-1/(30)=1/f

Or, (-1-2)/(60)=1/f

Or, 1/f=-3/(60)=-1/(20)

Or, f=-20 cm

Question 3: Under which of the following conditions a concave mirror can form an image larger than the actual object?

1. When the object is kept at a distance equal to its radius of curvature
2. When object is kept at a distance less than its focal length
3. When object is placed between the focus and centre of curvature
4. When object is kept at a distance greater than its radius of curvature

Answer: (c) & (b)

Explanation: In both the cases image formed is larger than object.

Question 4: Following figure shows a ray of light as it travels from medium A to medium B. Refractive index of the medium B relative to medium A is

1. (sqrt3)/(sqrt2)
2. (sqrt2)/(sqrt3)
3. 1/(sqrt2)
4. sqrt2

Answer: (a) (sqrt3)/(sqrt2)

Explanation: As per Snell’s Law,

(n_B)/(n_A)=(text(sin)60°)/(text(sin)45°)

=(sqrt3)/2÷1/(sqrt2)

=(sqrt3)/2×sqrt2=(sqrt3)/(sqrt2)

Question 5: A light ray enters from medium A to medium B as shown in following figure. The refractive index of medium B relative to A will be

1. greater than unity
2. less than unity
3. equal to unity
4. zero

Answer: (a) Greater than unity

Question 6: Beams of light are incident through the holes A and B and emerge out of box through the holes C and D respectively as shown in following figure. Which of the following could be inside the box?

1. A rectangular glass slab
2. A convex lens
3. A concave lens
4. A prism

Answer: (a) A rectangular glass slab

Question 7: A beam of light is incident through the holes on side A and emerges out of the holes on the other face of the box as shown in following figure. Which of the following could be inside the box?

1. Concave lens
2. Rectangular glass slab
3. Prism
4. Convex lens

Answer: (d) Convex lens

Question 8: Which of the following statements is true?

1. A convex lens has 4 dioptre power having a focal length 0.25 m
2. A convex lens has –4 dioptre power having a focal length 0.25 m
3. A concave lens has 4 dioptre power having a focal length 0.25 m
4. A concave lens has –4 dioptre power having a focal length 0.25 m

Answer: (a) A convex lens has 4 dioptre power having a focal length 0.25 m

Question 9: Magnification produced by a rear view mirror fitted in vehicles

1. is less than one
2. is more than one
3. is equal to one
4. can be more than or less than one depending upon the position of the object in front of it

Answer: (a) is less than one

Note: All figures on this page are taken from NCERT Exemplar Problems Class 10 Science Book