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  4. A point object is placed on the principal axis of a concave mirror, at a distance of 15 cm from the pole. The radius of curvature of the mirror is 20 cm and the object is made to oscillate along the principal axis with an amplitude of 2 mm . The amplitude of its image will be

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Q. A point object is placed on the principal axis of a concave mirror, at a distance of $15 \, cm$ from the pole. The radius of curvature of the mirror is $20 \, cm$ and the object is made to oscillate along the principal axis with an amplitude of $2 \, mm$ . The amplitude of its image will be

NTA AbhyasNTA Abhyas 2020Ray Optics and Optical Instruments

Solution:

Using mirror formula,
$\frac{1}{- 1 0} = \frac{1}{\text{v}} + \frac{1}{- 1 5} \Rightarrow \text{v} = - 3 0 cm$
|Axial magnification $\mid=\frac{\mathrm{V}^2}{\mathrm{u}^2}=\left(\frac{30}{15}\right)^2=4$
Amplitude of image = 4 x 2 = 8 mm.