Optics Question 503

Question: A lamp is hanging at a height 40 cm from the centre of a table. If its height is increased by 10 cm the illuminance on the table will decrease by

Options:

A) 10 %

B) 20%

C) 27%

D) 36%

Show Answer

Answer:

Correct Answer: D

Solution:

I1=Lr12=L1600 and I2=L2500

% decease in illuminance =I1I2I1×100

=(116002500)×100

=9002500×100=36



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