## Class 10th Science Chapter 10 Light Reflection and Refraction

Question 1. Which one of the following materials cannot be used to make a lens?
(a) Water (b) Glass
(c) Plastic (d) Clay
Question 2. The ¡mage formed by a concave mirror is observed to be virtual, erect and larger than the object. Where should be the position of the object?
(a) Between the principal focus and the centre of Curvature
(b) At the centre of curvature
(c) Beyond the centre of curvature
(d) Between the pole of the mirror and Its principal focus.
Answer: (d) Between the pole of the mirror and its principal focus.
Question 3. Where should an object b. placed In front of a convex lens to get a real
image of the size of the object?
(a) At the principal focus of the lens
(b) At twice the focal length
(c) At infinity
(d) Between the optical centre of the lens and its principal focus
Answer: (b) At twice the focal length
Question 4. A spherical mirror and a thin spherical lens have each a focal length of 15 cm. The mirror and the lens are likely to be:
(a) both concave
(b) both convex
(c) the mirror is concave, but the lens is convex
(d) the mirror is convex, but the lens is concave
Question 5. No matter how far you stand from a mirror, your Image appears erect. The
mirror is likely to be
(a) plane
(b) concave
(c) convex
(d) Either plane or convex
Answer: (d) Either plane or convex.
Question 6. Which of the following lenses would you prefer to use while reading small letters found ¡n a dictionary?
(a) A convex lens of focal length 50cm
(b) A concave lens of focal length 50cm
(c) A convex lens of focal length 5 cm
(d) A concave lens of focal length 5 cm.
Answer: (c) A convex lens of focal length 5 cm.
Question 7. We wish to obtain an erect image of an object, using a concave mirror of focal length 15 cm. what should be the range of distance of the object from
the mirror? What is the nature of the image? Is the image larger or smaller than the object? Draw a ray diagram to show the image formation in this
case.
We are given the focal length cf the concave mirror as f = -15cm.
For getting an erect image using a concave mirror, the object should be placed at a distance less than the focal length.
i.e. 15 cm from the pole. The image formed will be virtual, enlarged and erect. Question 8. Name the type of mirror used in the following situations.
(b) Side/rear-view mirror of a vehicle
(c) Solar furnace
Answer: (a) Concave mirror, to get powerful and parallel beams of light.
(b) Convex mirror because it always gives an erect image and enables the driver to view much larger area.
(c) Concave or parabolic mirror because it can concentrate sunlight at the focus to produce heat in the solar furnace.
Question 9. One half of a convex lens is covered with a black paper. Will this lens produce a complete image of the object? Verify your answer experimentally. Explain your observations.
Answer: Yes, even when one half of the lens is covered with a black paper, complete image of the object will be formed. Take a convex lens and focus the light from a distant object onto a screen. As expected an image (sharp) is formed at a distance equal to the focal length Cover the lower or the upper half of the lens and focus the light from the same object onto the same screen. You will be able to get a sharp image again; however the brightness of the image will be less in the second case. The same effect w,ll be seen even if the lens is half covered with black strips.
Question 10. An object 5cm in length is held 25cm away from a converging lens of focal length 10 cm. Draw a ray diagram and find the position, size and the nature of the image formed.  Therefore, the mage ¡s formed between F2 and 2F2 on the other side of the lens. It is real and inverted, and smaller in size than the object.
Question 11. A concave lens of focal length 15 cm forms an ¡mage 10 cm from the lens. How far is the object placed from the Pens? Draw the ray diagram. Question 12. An object is placed at a distance of 10 cm from a convex mirror of focal length 15 cm. Find the position and nature of the ¡mage.
Answer: f = +15 cm. u = -1o cm
For mirror, we have The image must be virtual and erect.
Question 13. The magnification produced by a plane mirror is +1. What does this mean?
Answer: This means that size of the image is equal to the size of the object.
Question 14. An object 5.0 cm in length Is placedat a distanc, of 20 cm in front of a convex mirror of radius of curvature 30 cm. Find the position of the image nature and size.    