SATHEE: Optics Question 513

Optics Question 513

Question: A lamp is hanging at a height of 4m above a table. The lamp is lowered by 1m. The percentage increase in illuminace will be

Options:

A) 40 %

B) 64%

C) 78%

D) 92%

Show Answer

Answer:

Correct Answer: C

Solution:

$I_{1} = \frac{L}{r_{1}^{2}} = \frac{L}{16}$

and $I_{2} = \frac{L}{r_{2}^{2}} = \frac{L}{9}$

% increase in illuminance $= \frac{I_{2} - I_{1}}{I} \times 100$

$= (\frac{16}{9} - 1) \times 100$

$\approx 78$

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Optics Question 513

Question: A lamp is hanging at a height of 4m above a table. The lamp is lowered by 1m. The percentage increase in illuminace will be

Options:

Answer:

Solution:

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