Engineering

Physics

Physical Quantities

Question

A photocell is operating in saturation mode with a photo current 4.8 mA. When a monochromatic radiation of wavelength 3000 Å and power 1W is incident. When another monochromatic radiation of wavelength 1650 Å and power 5 mW is incident, it is observed that maximum velocity of photoelectron increases to two times. Assuming efficiency of photo-electron generation per incident photon to be same for both the cases, calculate.

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Linked Question 1

Threshold wavelength for the cell is

A

5525 Å

B

4125 Å

C

6925 Å

D

4825 Å

$\frac{1240}{λ} - \frac{1240}{λ} = K$

$\frac{1240}{165} - \frac{1240}{λ} = 4 K$

$\frac{1240}{165} - \frac{1240}{λ} = 4 \times (\frac{1240}{300} - \frac{1240}{λ})$

$\frac{1}{165} - \frac{41}{300} = \frac{1}{λ} - \frac{4}{λ}$

$\frac{3}{λ} = \frac{1}{75} - \frac{1}{165} = \frac{1}{15} (\frac{1}{5} - \frac{1}{11})$

Linked Question 2

Saturation current in second case is

A

15.1 μA

B

13.3 μA

C

19.4 μA

D

9.2 μA

$i = η \frac{Pλ}{hc}$

$i' = \frac{ηP' λ'}{hc}$