A concave mirror with a radius of 20 cm creates a real image 30 cm from the mirror. The object is placed
A) 7.5 cm in front of the mirror.
B) 15 cm in front of the mirror.
C) 30 cm in front of the mirror.
D) 15 cm behind the mirror.
E) 7.5 cm behind the mirror.

Question

Quizplus · Accepted Answer

For a concave mirror, the mirror equation is $ \frac{1}{f} = \frac{1}{d_o} + \frac{1}{d_i} $, where $f$ is the focal length, $d_o$ is the object distance, and $d_i$ is the image distance. The focal length $f$ is half the radius of curvature, so $f = 10$ cm. Given $d_i = 30$ cm (positive because it's a real image), we can solve for $d_o$: $ \frac{1}{10} = \frac{1}{d_o} + \frac{1}{30} $, which simplifies to $d_o = 15$ cm.

A Concave Mirror with a Radius of 20 Cm Creates