Question

An object is placed 30. m away from a converging lens and the image appears at a distance of 70. m from the lens. What is the focal length of the lens?

Answer 1

Using the thin-lens equation, we can find the focal length of a converging lens by solving 1/f = 1/do + 1/di, where do is the object distance and di is the image distance. With the object placed 30 m away and the image at 70 m, the focal length of the lens is calculated to be 21 m.

Step-by-step explanation:

To determine the focal length of a converging lens, we use the thin-lens equation which is given by:

1/f = 1/do + 1/di

Where:

• f is the focal length of the lens,
• do is the object distance from the lens, and
• di is the image distance from the lens.

Given that do = 30 m and di = 70 m, we plug these values into the equation to find the focal length f:

1/f = 1/30 m + 1/70 m
= (70 + 30)/(30 * 70) m
= 100/(30 * 70) m
= 1/(21) m

Therefore, the focal length f is:

f = 21 m

Hence, the focal length of the lens is 21 meters.