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?
- Concave mirror as well as convex lens
- Convex mirror as well as concave lens
- Two plane mirrors placed at 90° to each other
- Concave mirror as well as concave lens
Answer: (a) Concave mirror as well as convex lens
Explanation: When point source of light is at the focus of concave mirror or convex lens, then a parallel beam of light is obtained after reflection (from concave mirror) and refraction (from 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
- – 30 cm
- – 20 cm
- – 40 cm
- – 60 cm
Answer: (b) – 20 cm
Explanation: Given, height of object = 10 mm, height of image = 5 mm, image distance = -30 cm,
Or, `u=-(30)/(0.5)=-60` cm
Mirror formula `1/v+1/u=1/f`
Or, `f=-20` cm
Question 3: Under which of the following conditions a concave mirror can form an image larger than the actual object?
- When the object is kept at a distance equal to its radius of curvature
- When object is kept at a distance less than its focal length
- When object is placed between the focus and centre of curvature
- 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. When object is between focus and pole of a concave mirror, then a larger, virtual and erect image is formed. When object is between C and F then image is formed beyond C. In this case, image is larger, real and inverted.
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
Answer: (a) `(sqrt3)/(sqrt2)`
Explanation: As per Snell's Law,
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
- greater than unity
- less than unity
- equal to unity
Answer: (a) Greater than unity
Explanation: This is similar to previous question, where ∠i > ∠r
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?
- A rectangular glass slab
- A convex lens
- A concave lens
- A prism
Answer: (a) A rectangular glass slab
Explanation: Emerging rays are parallel to incident rays. This means that there is a rectangular glass slab inside the box.
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?
- Concave lens
- Rectangular glass slab
- Convex lens
Answer: (d) Convex lens
Explanation: Beams of light (parallel to each other) are converging after passing through the optical object. This can only be done by a converging lens.
Question 8: Which of the following statements is true?
- A convex lens has 4 dioptre power having a focal length 0.25 m
- A convex lens has –4 dioptre power having a focal length 0.25 m
- A concave lens has 4 dioptre power having a focal length 0.25 m
- 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
Explanation: Signs are same (positive) for both power and focal length in option a. Moreover, positive sign shows it is convex lens.
Question 9: Magnification produced by a rear view mirror fitted in vehicles
- is less than one
- is more than one
- is equal to one
- 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
Explanation: A convex mirror is used as rearview mirror. A convex mirror always makes smaller image, because its field of view is largest among all types of mirrors.
Note: All figures on this page are taken from NCERT Exemplar Problems Class 10 Science Book