WAEC - Physics (1988 - No. 26)

An object is placed 36cm from a converging lens of focal length 24cm.If a real image which is 4cm high is formed, Calculate the height of the object.

2.0cm

4.0cm

6.0cm

8.0cm

10.0cm

F = 24cm , U = -36cm(behind lense)

Applying Lense formula = \(\frac {1}{f} = \frac{1}{v} - \frac{1}{u}\)

\(\frac{1}{v} = \frac{1}{24} - \frac{1}{36} = \frac{1}{72}\)

v = 72cm

but Magnification = \(\frac{V}{U} = \frac{h^i}{h_o}\)

\(\frac{72}{-36} = \frac{-4}{h_o}\) \( h_1\) = -4( real image is negative)

by cross multiplying \(h_1\) = 2cm