Test Index

WAEC Physics 2013 Paper

Question : 25

Total: 46

Solution:

Concept:

For a diverging lens, the focal length is negative, and the virtual image forms on the same side as the object.

Explanation:

Given focal length,

f = -30\,\text{cm}

The image is virtual, so image distance,

d_i = -20\,\text{cm}

Use the lens formula:

\frac{1}{f} = \frac{1}{d_o} + \frac{1}{d_i}

Substitute the values:

\frac{-1}{30} = \frac{1}{d_o} + \frac{-1}{20}

Simplify:

\frac{1}{d_o} = \frac{-1}{30} + \frac{1}{20}

\frac{1}{d_o} = \frac{-2+3}{60} = \frac{1}{60}

Therefore,

d_o = 60\,\text{cm}

Answer:

The object distance is

60\,\text{cm}

. Hence, the correct option is D.

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