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

Practice Questions

Q1
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 from the lens?
  1. Real and inverted
  2. Virtual and upright
  3. Real and upright
  4. Virtual and inverted

Questions & Step-by-Step Solutions

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 from the lens?
  • Step 1: Identify the type of lens. The lens is a concave lens.
  • Step 2: Note the focal length of the lens. The focal length is -20 cm (negative for concave lenses).
  • Step 3: Determine the position of the object. The object is placed at 30 cm from the lens.
  • Step 4: Compare the object distance (30 cm) with the focal length (-20 cm). Since 30 cm is greater than -20 cm, the object is beyond the focal length.
  • Step 5: Understand the properties of a concave lens. A concave lens always forms a virtual image when the object is placed beyond the focal length.
  • Step 6: Conclude that the image formed is virtual and upright.
  • Lens Formula – Understanding the relationship between object distance, image distance, and focal length using the lens formula (1/f = 1/v - 1/u).
  • Image Characteristics – Identifying the nature of the image (real/virtual, upright/inverted) formed by concave lenses based on object placement relative to the focal length.
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