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

The object distance is
`D_(o)=15 cm`

Step-by-step explanation:

According to the Descartes equation, you have:

`(1)/(D_(o))+(1)/(D_(i)) = (1)/(f)`

`Do= ??` [object distance]

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

`f= 30cm` [focal length]

Clearing in the Descartes equation:

`D_(o)= (D_(i) f)/((f-D_(i))) = (30*30)/((30 - (-30))) = (900)/(60)} = 15`

The object distance is
`D_(o)=15` cm