What is the focal length of a lens if it forms an image at infinity when the obj
Practice Questions
Q1
What is the focal length of a lens if it forms an image at infinity when the object is placed at 30 cm?
30 cm
15 cm
60 cm
20 cm
Questions & Step-by-Step Solutions
What is the focal length of a lens if it forms an image at infinity when the object is placed at 30 cm?
Step 1: Understand that when an object is placed at a certain distance from a lens, it can form an image at a specific location.
Step 2: Recognize that if the image is formed at infinity, it means the light rays coming from the object are parallel when they reach the lens.
Step 3: Know that for a lens to form an image at infinity, the focal length (f) of the lens must be equal to the object distance (d) when the object is placed at a certain distance.
Step 4: In this case, the object is placed at 30 cm, so we set the focal length equal to this distance.
Step 5: Therefore, the focal length of the lens is f = 30 cm.
