A red laser pointer emits light at a wavelength of 488 nm. If the laser emits 7.5  10–4 J of energy per second in the form of visible radiation, how many photons per second are emitted from the laser? a)
4.1  10–19 photons/sec
b)
5.4  10–16 photons/sec
c)
8.9  1014 photons/sec
d)
1.8  1015 photons/sec
e)
2.5  1018 photons/sec

The answer to the question, how many photons per second are emitted from the laser is d. 1.84 × 10¹⁵ photons/sec

Since the red laser pointer emits light of wavelength 488 nm, we need to find the energy of each photon from

E = hc/λ where h = Planck's constant = 6.63 × 10⁻³⁴ Js, c = speed of light = 3 × 10⁸ m/s and λ = wavelength of light = 488 nm = 488 × 10⁻⁹ m

Substituting the values of the variables into the equation, we have

E = hc/λ

E = 6.63 × 10⁻³⁴ Js × 3 × 10⁸ m/s ÷ 488 × 10⁻⁹ m

E = 19.89 × 10⁻²⁶ Jm ÷ 488 × 10⁻⁹ m

E = 0.04076 × 10⁻¹⁷ J per photon

E = 4.076 × 10⁻¹⁹ J per photon

Since the laser emits 7.5 × 10⁻⁴ J per second, the number of photons emitted from the laser per second = energy per second/energy per photon

= 7.5 × 10⁻⁴ J per second ÷ 4.076 × 10⁻¹⁹ J per photon

= 1.84 × 10¹⁵ photons/sec

The answer to the question, how many photons per second are emitted from the laser is d. 1.84 × 10¹⁵ photons/sec

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3 1/4 %

explanation: