Question

A concave shaving mirror has a radius of curvature of 35.0cm.It is positioned so that the (upright) image of a man’s face is 2.50 times the size of the face. How far is the mirror from face?

• A. 5.25 cm
• B. 21.0 cm
• C. 10.5 cm
• D. 42 Cm

Answer 1

Answer: (C)

10.5 cm

Answer 2

: For spherical mirror,$\mathrm { R } = 35.0 \mathrm {~cm}$

$\therefore \mathrm { f } = \frac { 35 } { 2 } = 17.5 \mathrm {~cm}$

Now,

Also, magnification $\therefore \frac { 1 } { \mathrm { f } } = \frac { 1 } { \mathrm { u } } - \frac { 1 } { \mathrm { mu } }$

or

$= 17.5 \left( 1 - \frac { 1 } { 2.5 } \right) = 17.5 \times ( 06 ) = 10.5 \mathrm {~cm}$