Question

An object is 30.0 cm from a spherical mirror, on the centre axis. The absolute value of Lateral magnification is $\frac { 1 } { 2 }$. The image produced is inverted, then focal length of mirror is

• A. 30 cm
• B. 10 cm
• C. 15 cm
• D. 20 cm

Answer 1

Answer: (B)

10 cm

Answer 2

u = – 30 m = – $\frac { 1 } { 2 }$

u = $\left( \frac { \mathrm { m } - 1 } { \mathrm {~m} } \right) \mathrm { f }$ Ž f = $\frac { \mathrm { mu } } { \mathrm { m } - 1 } = \frac { \left( - \frac { 1 } { 2 } \right) ( - 30 ) } { - \frac { 1 } { 2 } - 1 } = \frac { \frac { 30 } { 2 } } { - \frac { 3 } { 2 } }$

$\mathrm { f } = - 10 \mathrm {~cm}$