Mirror — NumericalMediumQuestion 20201
Question
An object 4 cm tall is placed 30 cm in front of a concave mirror of focal length 20 cm. Size of image is:
- A8 cmCorrect
- B12 cm
- C6 cm
- D4 cm
Correct answer
8 cm
Explanation
1/v = 1/f − 1/u = 1/(−20) − 1/(−30) = −1/20 + 1/30 = −3/60 + 2/60 = −1/60 → v = −60 cm. m = −v/u = −(−60)/(−30) = −2. Image height = |m| × 4 = 8 cm (inverted).