What is the focal length of a lens if it forms an image at infinity when the obj

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Question: What is the focal length of a lens if it forms an image at infinity when the object is placed at 30 cm?

Options:

Correct Answer: 60 cm

Solution:

For the image to be at infinity, the focal length must be equal to the object distance, hence f = 60 cm.

What is the focal length of a lens if it forms an image at infinity when the object is placed at 30 cm?

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.

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