Physicshard · Past Paper
A concave mirror has a radius of curvature of 40 cm. To get an image twice the size of the object, the object distance should be:
A10 cm or 30 cm
B20 cm or 60 cm
C15 cm or 45 cm
D30 cm only
✓ Correct Answer: A — 10 cm or 30 cm
f = -20. m = f/(f-u). If m=2 (virtual), u=-10. If m=-2 (real), u=-30.
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