If a concave lens has a focal length of -20 cm, what is the nature of the image

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Question: If a concave lens has a focal length of -20 cm, what is the nature of the image formed when an object is placed at 30 cm?

Options:

Correct Answer: Virtual and upright

Solution:

The image formed by a concave lens is virtual and upright when the object is placed beyond the focal length.

If a concave lens has a focal length of -20 cm, what is the nature of the image formed when an object is placed at 30 cm?

If a concave lens has a focal length of -20 cm, what is the nature of the image formed when an object is placed at 30 cm?

Step 1: Identify the type of lens. We have a concave lens.
Step 2: Note the focal length of the lens, which is -20 cm (the negative sign indicates it's a concave lens).
Step 3: Determine the position of the object. The object is placed at 30 cm, which is beyond the focal length (-20 cm).
Step 4: Understand that for a concave lens, when the object is placed beyond the focal length, the image formed is virtual.
Step 5: Remember that a virtual image is always upright when formed by a concave lens.

Lens Formula – Understanding the lens formula (1/f = 1/v - 1/u) is crucial for determining the nature of the image formed by a lens.
Image Characteristics – Concave lenses always produce virtual, upright, and diminished images regardless of the object's position relative to the focal length.