Question

11. The concentration of photons in a uniform light beam with a wavelength of 500 nm is 1.7 x 1013 m-3. The intensity of the beam is: A) 6.7 x 10-6 W/m 2 D) 4.0 103 W/m 2 B) 1.0 x 103 W/m 2 E) 3.2 x 102 W/m 2 C) 2.0 x 103 W/m 2 ​

Answer 1

Answer:

your correct answers is

Explanation:

option C

Answer 2

Given: The wavelength of light is 500nm and concentration of photons is $1.7X10^{13}m^{-3}$

To find: The intensity of a beam

Solution:

• First find energy of photon(E)=$\frac{hc}{lambda}$=$\frac{6.63X10^{-34}X3X10^{8} }{500X10^{-9} }$=$3.978X10^{-19}J$
• Energy density of photon per cubic metre is = $3.978X10^{-19}X1.7X10^{13}=6.76X10^{-6}Jm^{-3}$

• We know distance travelled by a light ray in 1 second is $3X10^{8}m$

• Now volume of light passing through in 1 second is A X $3 X 10^{8}m^{3}$ where A is Area.
• The power is = Energy density X Volume of light

                               = $6.76 X 10^{-6}XAX3X10^{8} W$

• The Intensity is = $\frac{Power}{Area}=\frac{6.76X10^{-6}XAX3X10^{8} }{A} =2.0 X 10^{3}Wm^{-2}$

So,the concentration of photons is C)$2.0 X 10^{3}Wm^{-2}$