Number of photons emitted by a laser

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SUMMARY

The discussion centers on calculating the number of photons emitted by a laser using the formula P.t = nhf, where n is the number of photons, h is Planck's constant, and f is the frequency. The conversion of energy from electronvolts (eV) to joules is critical, specifically converting 5 eV to joules by multiplying with the elementary charge, resulting in 8 × 10-19 joules. The final calculation yields n/t = 1.25 × 1016, confirming the accuracy of the approach taken by the participants.

PREREQUISITES
  • Understanding of Planck's constant (h = 6.626 × 10-34 Js)
  • Knowledge of energy conversion from electronvolts to joules
  • Familiarity with the concept of power in watts (1 watt = 1 joule/second)
  • Basic grasp of photon emission and laser physics
NEXT STEPS
  • Study the derivation of Planck's equation for photon energy
  • Learn about the relationship between frequency and wavelength in laser light
  • Explore advanced calculations involving laser power and photon flux
  • Investigate applications of photon calculations in quantum optics
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Students and professionals in physics, particularly those focusing on quantum mechanics, laser technology, and photonics, will benefit from this discussion.

songoku
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Homework Statement
A laser emits photon of energy 5 eV with power of 0.01 W. How many photons are emitted per second?
a. 3.1 × 10^21
b. 5.0 × 10^18
c. 2.5 × 10^21
d. 4.0 × 10^14
e. 2.7 × 10^15
Relevant Equations
E = nhf
E = P.t
P.t = nhf
n/t = P/(hf) = 1.25 × 10^16

Something wrong with my working or I just pick (E) as answer? Thanks
 
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This is an exercise in conversion of units. You need to express 5 eV in joules, and also realize that a watt is one joule per second. What you submitted in the OP appears to show a lack of effort.
 
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Charles Link said:
This is an exercise in conversion of units. You need to express 5 eV in joules, and also realize that a watt is one joule per second. What you submitted in the OP appears to show a lack of effort.
To change eV to Joules, I need to multiply with elementary charge so 5 eV = 5 × 1.6 × 10^(-19) = 8 × 10^(-19)

So, n/t = 0.01 / (8 × 10^(-19)) = 1.25 × 10^16
 
songoku said:
To change eV to Joules, I need to multiply with elementary charge so 5 eV = 5 × 1.6 × 10^(-19) = 8 × 10^(-19)

So, n/t = 0.01 / (8 × 10^(-19)) = 1.25 × 10^16
Yes, I get your answer.
 
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Thank you very much for the help Charles Link and haruspex
 

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