b
(b) Focal length of mirror \(f = \frac{R}{2} = \frac{{10}}{2} = 5cm\)

For part \(PQ\) : transverse magnification

length of image \(L_1 = \left({\frac{f}{{f - u}}} \right) \times {L_0}\)

= \(\left({\frac{{ - 5}}{{ - 5 - (- 20)}}} \right) \times {L_0} = \frac{{ - {L_0}}}{3}\)

For part \(QR :\) longitudinal magnification

Length of image \({L_2} = {\left({\frac{f}{{f - u}}} \right)^2}{L_0}\)

= \({\left({\frac{{ - 5}}{{ - 5 - (- 20)}}} \right)^2} \times {L_0} = \frac{{{L_0}}}{9}\) 

==> \(\frac{{{L_1}}}{{{L_2}}} = \frac{3}{1}\)