Q.1. Mention the types of lenses stating the characteristics of each type.
Ans. There are two types of lenses-convex lens and concave lens.
Convex lens is thicker at the center and gradually becomes thinner towards the edges. It converges a parallel beam of light after refraction through it. hence it is also called a converging lens.
Concave lens is thinner at the center and gradually becomes thicker towards the edges. It diverges a parallel beam of light after refraction through it. Hence, it is also called a diverging lens.
Q.2. How will you determine the focal length of a convex lens?
– Arrange a setup as shown in the figure given along side.
– Take any object, like a burning candle and put it at any distance from a screen.
– Now take the lens of which the focal length is to be calculated and adjust it in front of the screen by moving it to-and-fro until a sharp image of the candle is formed on the screen.
– Measure this distance between the screen and the lens. This distance is the focal length of the lens.
Q.3. Write a short note on magnifying glass.
Ans. A magnifying glass or Simple microscope is just a convex lens of short focal length. When an object is placed between the focus and the optical center of a convex lens, an enlarged, erect and virtual image of the object is formed.