SATHEE: Optics Question 132

Optics Question 132

Question: In a grease spot photometer light from a lamp with dirty chimney is exactly balanced by a point source distance 10 cm from the grease spot. On clearing the chimney, the point source is moved 2 cm to obtain balance again. The percentage of light absorbed by dirty chimney is nearly

Options:

A) 56%

B) 44%

C) 36%

D) 64%

Show Answer

Answer:

Correct Answer: C

Solution:

The actual luminous intensity of the lamp is $I_{1}$ whereas the intensity is $I_{1}^{'}$ in the dirty state. I position, $\frac{I_{1}^{'}}{I_{2}} = {(\frac{x}{10})}^{2}$ II position, $\frac{I_{1}}{I_{2}} = {(\frac{x}{8})}^{2}$

$\Rightarrow \frac{I_{1}^{'}}{I_{1}} = 0.64$

$\Rightarrow I_{1}^{'} = 0.64 I_{1}$ . Thus, % of light absorbed = 36%.

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Optics Question 132

Question: In a grease spot photometer light from a lamp with dirty chimney is exactly balanced by a point source distance 10 cm from the grease spot. On clearing the chimney, the point source is moved 2 cm to obtain balance again. The percentage of light absorbed by dirty chimney is nearly

Options:

Answer:

Solution:

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