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

Answer: A convex lens is a converging lens that bulges outward and causes parallel light rays to converge to a focal point by bending them inward.

Question 2: Describe the main difference between a convex and a concave lens in terms of image formation.

Answer: A convex lens converges light rays to form real or virtual images, while a concave lens diverges light rays, typically forming virtual images.

Question 3: Explain why convex lenses are used in magnifying glasses.

Answer: Convex lenses magnify objects because they cause the image to appear larger and closer to the eye when the object is within the focal length.

Question 1: A convex lens has a focal length of 10 cm. An object is placed 30 cm from the lens. Calculate the position of the image using the lens formula: 1/f = 1/v + 1/u. State whether the image is real or virtual.

Answer: Using 1/f = 1/v + 1/u, 1/10 = 1/v + 1/(-30). So, 1/v = 1/10 + 1/30 = (3 + 1)/30 = 4/30 = 2/15. Therefore, v = 15/2 = 7.5 cm. The image is real and formed on the same side as the screen.

Question 2: An object is placed 15 cm in front of a concave lens with a focal length of 5 cm. Calculate the image distance and determine if the image is magnified.

Answer: Using 1/f = 1/v + 1/u, 1/(-5) = 1/v + 1/(-15). So, 1/v = -1/5 + 1/15 = (-3 + 1)/15 = -2/15. Thus, v = -15/2 = -7.5 cm. The negative sign indicates a virtual, upright, magnified image on the same side as the object.

Question 1: List three variables that can be changed in an experiment to investigate the focal length of a lens.

Answer: Variables include the object distance, the type of lens used, and the position of the screen to locate the image.

Question 2: Describe the safety precautions that should be taken when handling lenses and light sources during practical investigations.

Answer: Handle lenses carefully to avoid scratches, avoid direct staring into intense light sources, and ensure the workspace is free of obstructions to prevent accidents.

Question 1: A student measures the image distance for a convex lens with a fixed object distance. The image is real and inverted when the object is 20 cm from the lens, and the image forms 15 cm from the lens. What is the approximate focal length of the lens?

Answer: Using the lens formula: 1/f = 1/v + 1/u, 1/f = 1/15 + 1/(-20) = (4/60) - (3/60) = 1/60. Therefore, f ≈ 60 cm.

Question 1: Explain how a convex lens is used in a camera to produce a clear image. Include in your answer the role of the focal length and the image distance, and how adjusting the lens position affects the focus.

Answer: A convex lens in a camera converges light from an object to form a focused image on the film or sensor. The focal length determines how strongly the lens converges light; shorter focal lengths produce wider, less magnified images, while longer focal lengths produce narrower, more magnified images. Adjusting the lens position changes the image distance, allowing the camera to focus the image sharply onto the film or sensor. Proper focusing ensures a clear, sharp picture by aligning the image distance with the focal length.

Question 1: Identify an application of concave lenses in everyday devices and explain its purpose.

Answer: Concave lenses are used in eyeglasses for people with short-sightedness to diverge light rays and help focus images correctly onto the retina.

Question 2: Describe one way in which convex lenses are utilised in modern technology.

Answer: Convex lenses are used in magnifying glasses and microscopes to enlarge images of small objects for detailed examination.