Question 1: Lenses are transparent objects that refract light to form images. Convex lenses are thicker in the middle and converge light rays, while concave lenses are thinner in the middle and diverge light rays. Understanding how these lenses work is essential for many optical devices.

Answer: Lenses are transparent objects that refract light; convex lenses converge rays, concave lenses diverge rays.

Question 1: Define a convex lens and describe one common use.

Answer: A convex lens is thicker in the middle and converges light; used in magnifying glasses and cameras.

Question 2: Explain how a concave lens affects parallel light rays passing through it.

Answer: A concave lens causes parallel rays to diverge as if they are originating from a focal point behind the lens.

Question 1: A convex lens has a focal length of 15 cm. An object is placed 45 cm in front of it. Calculate the image distance using the lens formula: 1/f = 1/do + 1/di. (f positive for convex lens).

Answer: di ≈ 22.5 cm

Question 2: A concave lens has a focal length of -10 cm. An object is placed 30 cm in front of it. Find the image distance.

Answer: di ≈ -6.67 cm

Question 1: Describe a simple experiment to determine the focal length of a convex lens. List the variables involved and safety precautions.

Answer: Set up a distant object and move the lens until a clear image is formed on a screen. Measure object and image distances; focal length = (object distance × image distance) / (object distance + image distance). Variables: object distance, image distance, lens position. Precautions: handle the lens carefully, avoid direct sunlight, ensure stable setup.

Question 2: Explain how convex and concave lenses are used in modern cameras and microscopes.

Answer: Convex lenses focus light to form magnified images in microscopes and focus light onto photographic film in cameras. Concave lenses are used in eyeglasses to correct myopia by diverging light before it enters the eye.

Question 1: A student observes that when using a convex lens with a focal length of 20 cm, an object placed 60 cm in front produces an image 30 cm behind the lens. Is this image real or virtual? Is it magnified or reduced? Explain your reasoning.

Answer: The image is real and magnified because the image distance is positive and greater than the object distance, indicating a real, enlarged image formed on the same side as the observer.

Question 2: Identify a technological device that employs convex or concave lenses and describe its function.

Answer: A magnifying glass uses a convex lens to produce a magnified image of small objects for detailed viewing.