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Q: An optical device X has a focal length of –30 cm. X can be:
  • A. either a convex lens or a convex mirror
  • B. either a concave lens or a concave mirror
  • C. either a convex lens or a concave mirror
  • D. either concave lens or a convex mirror
Correct Answer: Option B - X either a concave lens or a concave mirror because the focus of concave mirror or concave lens is always negative.
B. X either a concave lens or a concave mirror because the focus of concave mirror or concave lens is always negative.

Explanations:

X either a concave lens or a concave mirror because the focus of concave mirror or concave lens is always negative.