Question

Dentists use special lamps that consist of a concave mirror and a small, bright light source that is fixed on the principal axis of the mirror. When the light source is placed 5.0 cm from the mirror, the reflected light is focused in a bright spot at distance 70.0 cm from the mirror.

(a) Determine the radius of curvature of the mirror?

Answer 1

The radius of curvature is 9.35 cm.

Step-by-step explanation:

Given:

u = -5 cm

v = -70 cm

The radius of curvature of the mirror can be obtained from the expression:

`(1)/(v) +(1)/(u) =(2)/(R) \\-(1)/(v) -(1)/(u) =(2)/(R) \\-(1)/(70) -(1)/(5) =(2)/(R) \\-0.014-0.2=(2)/(R) \\R=-9.35cm`

Answer 2

Answer: 140cm

Step-by-step explanation:

Radius of curvature r = 2f

Where f is the focal point

f = 70cm, therefore

r =2 x 70 = 140cm