Question 1: Define a convex lens and explain how it converges light rays.

Answer: A convex lens is a lens that bulges outward and converges parallel light rays to a focal point due to its shape and refractive properties.

Question 2: Describe the main difference between a convex and a concave lens in terms of their shape and effect on light rays.

Answer: A convex lens is thicker in the middle and converges light rays, whereas a concave lens is thinner in the middle and diverges light rays.

Question 3: Explain how a convex lens can be used to correct hypermetropia (long-sightedness).

Answer: A convex lens corrects hypermetropia by converging light rays before they reach the eye, allowing the image to form on the retina for clear vision.

Question 4: What is the focal length of a lens, and how does it relate to the convergence or divergence of light rays?

Answer: The focal length is the distance from the lens to the focal point where light rays converge or appear to diverge from; it indicates the lens's converging or diverging power.

Question 5: Identify whether the following statement is true or false: 'Concave lenses cause parallel light rays to converge at a focal point.'

Answer: False

Question 6: Fill in the blank: A concave lens causes parallel light rays to ________, making the rays diverge.

Answer: diverge

Question 7: Describe a practical application of concave lenses in everyday life.

Answer: Concave lenses are used in optical devices such as peepholes and laser beam expanders to diverge light rays or magnify images.

Question 8: Outline the steps involved in setting up a simple experiment to demonstrate image formation by a convex lens.

Answer: First, position the convex lens on a stand and place an object at a known distance beyond the focal length. Then, move a screen until a sharp image is formed. Record the object and image distances, and analyse how the image size and position change with different object distances.

Question 9: Given an object 30 cm from a convex lens with a focal length of 15 cm, calculate the image distance using the lens formula: 1/f = 1/do + 1/di.

Answer: Using 1/f = 1/do + 1/di, 1/15 = 1/30 + 1/di. Solving for di gives di = 30 cm.

Question 10: A person with hypermetropia requires a converging lens of focal length +20 cm. What is the power of this lens in dioptres? (Power = 100/f, with f in cm).

Answer: Power = 100 / 20 = +5 dioptres.