Question

A rod of length 10 cm lies along the principal axis of a concave mirror of focal length 10 cm in such a way the its and closer to the pole is 20 cm away from the mirror the length of the image is:

• A. 10 cm
• B. 15 cm
• C. 2.5 cm
• D. 5 cm

Answer 1

Answer: (D)

5 cm

Answer 2

:

Here, f = - 10 cm

For end A,

Image position of end A,,

or

For end

Image position of end B,

$\frac { 1 } { v _ { B } } + \frac { 1 } { ( - 30 ) } = \frac { 1 } { ( - 10 ) }$ or

Length of the image $= \left| \mathrm { v } _ { \mathrm { A } } \right| - \left| \mathrm { v } _ { \mathrm { B } } \right| = 20 \mathrm {~cm} - 15 \mathrm {~cm} = 5 \mathrm {~cm}$