Question 174: Dual Nature of Matter and Radiation

Question

A 2 mW laser operates at wavelength of 500 nm. The number of photons that will be emitted per second is :
[Given Planck's constant h = 6.6 × 10
–34
Js, speed of light c = 3.0 × 10
8
m/s]

Accepted Answer

$$2 	imes {10^{ - 3}} = {{hc} \over \lambda }{{dn} \over {dt}}$$
$${{dn} \over {dt}} = {{2 	imes {{10}^{ - 3}}\lambda } \over {hc}}$$
$$ = {{2 	imes {{10}^{ - 3}} 	imes 500 	imes {{10}^{ - 9}}} \over {6.6 	imes {{10}^{ - 34}} 	imes 3 	imes {{10}^8}}}$$
$$ = {{1000} \over {6.6 	imes 3}} 	imes 10 = 5 	imes {10^{15}}$$

Answer

5 × 10
15

Answer

1.5 × 10
16

Answer

1 × 10
16

Answer

2 × 10
16

Dual Nature of Matter and Radiation

A 2 mW laser operates at wavelength of 500 nm. The number of photons that will be emitted per second is : [Given Planck's constant h = 6.6 × 10 –34 Js, speed of light c = 3.0 × 10 8 m/s]

Choose the correct answer: