Question

A certain helium-neon laser pointer, emitting light with a wavelength of 632 nm, has a beam with an intensity of 825 W/m2 and a diameter of 2.80 mm. How many photons are emitted by the laser pointer every second?

Answer 1

`N = 1.62 * 10^(15)`

Step-by-step explanation:

Energy of each photon is given as

`E = (hc)/(\lambda)`

here we will have

`\lambda = 632 nm`

now we will have

`E = ((6.626* 10^(-34))(3 * 10^8))/(632 * 10^(-9))`

`E = 3.14 * 10^(-19) J`

now let say there is N number of photons per second

so power due to photons is

`P = N(3.14 * 10^(-19))`

now intensity is given as power received per unit area

so we have

`I = (P)/(A)`

`825 = (N(3.14 * 10^(-19)))/(\pi (1.40 * 10^(-3))^2)`

`825 = N(5.11 * 10^(-14))`

`N = 1.62 * 10^(15)`