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Light Reflection and Refraction
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11/08/2021 1:20 pm
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A converging mirror forms a real image of height 4 cm of an object of height 1 cm placed 20 cm away from the mirror :
(i) Calculate the image distance.
(ii) What is the focal length of the mirror?
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11/08/2021 1:25 pm
\(h_2\) = -4 cm (real image)
\(h_1\) = 1 cm
u = -20 cm
v = ?
(i) m = \(\frac{h_2}{h_1}\) = -\(\frac{v}{u}\)
⇒ \(\frac{-4}{1}\) = -\(\frac{v}{-20}\)
⇒ v = -80 cm
Image forms in front of the concave mirror.
(ii) f = ?
\(\frac{1}{v}\) + \(\frac{1}{u}\) = \(\frac{1}{f}\)
\(\frac{1}{f}\) = \(-\frac{1}{80}\) - \(\frac{1}{20}\)
= \(\frac{-1 - 4}{80}\) = \(-\frac{5}{80}\)
f = -16 cm