JEE MAIN - Physics (2022 - 29th June Morning Shift - No. 24)
A parallel beam of light is allowed to fall on a transparent spherical globe of diameter 30 cm and refractive index 1.5. The distance from the centre of the globe at which the beam of light can converge is _____________ mm.
Answer
225
Explanation
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1st refraction : $${{1.5} \over {{v_1}}} - 0 = {{0.5} \over {15}}$$
$$\Rightarrow$$ v1 = 45 cm
2nd refraction : $${1 \over {{v_2}}} - {{1.5} \over {15}} = {{ - 0.5} \over { - 15}}$$
$$ \Rightarrow {1 \over {{v_2}}} = {1 \over {30}} + {1 \over {10}}$$
$$ = {4 \over {30}}$$
$$\Rightarrow$$ v2 = + 7.5 cm
$$\Rightarrow$$ Distance from centre = 22.5 cm = 225 mm
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