Question:medium

An object of 4.0 cm in size is placed at 25 cm in front of a concave mirror of focal length 15 cm. At what distance from the mirror should a screen be placed in order to obtain a sharp image?

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For concave mirrors, the object distance is negative when placed in front of the mirror. Use the mirror equation to calculate the image distance and position.
Updated On: Jan 15, 2026
  • +25 cm
  • +25.5 cm
  • -35.5 cm
  • -37.5 cm
Show Solution

The Correct Option is C

Solution and Explanation

To find the image distance \( v \), we use the mirror equation:\n\[\n\frac{1}{f} = \frac{1}{u} + \frac{1}{v}\n\]\nWhere:\n- \( f = 15 \, \text{cm} \)\n- \( u = -25 \, \text{cm} \)\n\nSubstituting:\n\[\n\frac{1}{15} = \frac{1}{-25} + \frac{1}{v}\n\]\nSolving for \( v \):\n\[\n\frac{1}{v} = \frac{1}{15} + \frac{1}{25} = \frac{5 + 3}{75} = \frac{8}{75}\n\]\n\[\nv = \frac{75}{8} = 9.375 \, \text{cm}\n\]\n\nTherefore, the image forms at \( 9.375 \, \text{cm} \).
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