An object is placed 15cm from a diverging lens of focal length 12cm. The image...
PHYSICS
WAEC 2015
An object is placed 15cm from a diverging lens of focal length 12cm. The image of the object formed by the lens in
- A. real and 6.67cm from the lens
- B. virtual and 6.67cm from the lens
- C. real and 60.00cm from the lens
- D. virtual and 60.00cm from the lens
Correct Answer: B. virtual and 6.67cm from the lens
Explanation
The focal length of a diverging lens is negative.
f = -12 cm; u = 15 cm.
\(f = \frac{uv}{u + v}\)
\(-12 = \frac{15v}{15 + v}\)
\(-12 (15 + v) = 15v \implies -180 - 12v = 15v\)
\(-180 = 15v + 12v \implies -180 = 27v\)
\(v = \frac{-180}{27} = -6.67 cm\)
The image is virtual and 6.67 cm from the lens.
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