Question 1: Lenses are transparent objects that bend light to form images. Convex lenses are thicker at the centre and cause parallel rays of light to converge, forming real or virtual images. Concave lenses are thinner at the centre and cause parallel rays to diverge, creating virtual images. Understanding how these lenses work is essential in designing optical devices such as glasses, microscopes, and cameras.

Answer: Lenses bend light; convex lenses converge light rays, forming real or virtual images, while concave lenses diverge light rays, creating virtual images.

Question 1: Define a convex lens and describe its main use in everyday life.

Answer: A convex lens is thicker at the centre and converges light rays; it is used in magnifying glasses and cameras.

Question 2: Explain the difference between real and virtual images formed by lenses.

Answer: A real image is formed where light rays actually meet and can be projected onto a screen; a virtual image is formed where rays appear to meet but do not, and cannot be projected.

Question 1: An object is placed 30 cm in front of a convex lens with a focal length of 15 cm. Calculate the image distance and determine if the image is real or virtual.

Answer: Using 1/f = 1/do + 1/di, 1/15 = 1/30 + 1/di; solving gives di = 10 cm; the image is real and on the same side as the object.

Question 2: A concave lens has a focal length of 20 cm. An object is placed 60 cm in front of it. Find the position of the virtual image formed by the lens.

Answer: Using 1/f = 1/do + 1/di, 1/(-20) = 1/60 + 1/di; solving gives di ≈ -15 cm; the virtual image is 15 cm on the same side as the object.

Question 1: Describe a simple experiment to determine the focal length of a convex lens. Include the variables you would control and safety precautions.

Answer: Set up a distant object and move the lens until a sharp image is formed on a screen. Measure the object distance (do) and image distance (di). Use the lens formula to calculate focal length. Control variables such as object distance and lens position. Safety precautions include handling the lens carefully to avoid scratches and avoiding direct sunlight focusing.

Question 2: List three safety precautions to observe when working with optical equipment involving lenses.

Answer: Handle lenses with care to avoid scratches, avoid looking directly into intense light sources focused through lenses, and ensure equipment is stable to prevent accidents.

Question 1: In an experiment, a convex lens forms a real image at 50 cm when the object is placed 150 cm from the lens. Determine the focal length of the lens and comment on the image size compared to the object.

Answer: Using 1/f = 1/do + 1/di, 1/f = 1/150 + 1/50; 1/f = 1/75; f = 75 cm. Since di < do, the image is smaller than the object.

Question 1: Explain how convex lenses are used in cameras to focus light and produce clear images.

Answer: Convex lenses focus parallel light rays onto a film or sensor, forming a sharp image. Adjusting the lens-to-sensor distance allows focusing on objects at different distances.

Question 2: Identify a day-to-day object that uses a concave lens and describe its purpose.

Answer: A concave lens is used in telescopes to diverge light and help view distant objects more clearly.