JAMB - Physics (1979 - No. 38)
A concave lens of focal length 20cm form an image 1/2 the size of the object. The object distance is
100cm
\( \frac{100}{q} \)
60cm
\( \frac{60}{7} \)
None of the above
توضيح
V = \(\frac{U}{2}\)
f = 20cm
\(\frac{1}{f} = \frac{1}{u} + \frac{1}{v}\) = \(\frac{1}{20} = \frac{1}{u} + \frac{2}{u}\)
\(\frac{1}{20} = \frac{3}{u}\)
u = 60cm.