Question

A concave mirror with a focal length of 30 cm is used to form an image that is 30 cn behindo the mirror. What is the object distance? vy A) +20 cm B)+15 cm C)+60 cm D)+30 cm E)+58 cm

Answer 1

Answer:

The object distance is $D_{o}=15 cm$

Explanation:

According to the Descartes equation, you have:

$\frac{1}{D_{o}}+\frac{1}{D_{i}} = \frac{1}{f}$

$Do= ??$ [object distance]

$Di= -30cm$ [negative image distance from being behind]

$f= 30cm$ [focal length]

Clearing in the Descartes equation:

$D_{o}= \frac{D_{i} f}{(f-D_{i})} = \frac{30*30}{(30 - (-30))} = \frac{900}{60}} = 15$

The object distance is $D_{o}=15$ cm