Lakhmir Singh Physics Class 10 Solutions Page No:257
Question 18: A camera fitted with a lens of focal length 50 mm is being used to photograph a flower that is 5 cm in diameter. The flower is placed 20 cm in front of the camera lens.
(a) At what distance from the film should the lens be adjusted to obtain a sharp image of the flower ?
(b) What would be the diameter of the image of the flower on the film ?
(c) What is the nature of camera lens ?
The film should be at a distance of 6.66cm behind the camera lens,
Question 19: An object is 2 m from a lens which forms an erect image one-fourth (exactly) the size of the object. Determine the focal length of the lens. What type of lens is this ?
Question 20: An image formed on a screen is three times the size of the object. The object and screen are 80 cm apart when the image is sharply focussed.
(a) State which type of lens is used.
(b) Calculate focal length of the lens.
Solution : (a) Since the image is formed on a screen, it must be a real image.
Hence, the lens should be a convex lens.
(b) m = -3 (Real and inverted image)