Number of photons emitted by a laser

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    Laser Photons
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Homework Help Overview

The discussion revolves around calculating the number of photons emitted by a laser, specifically focusing on the conversion of energy units from electronvolts (eV) to joules and the relationship between power, energy, and photon emission.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants explore the conversion of energy units and the application of the formula relating power, energy, and the number of photons. Some question the original poster's calculations and the effort demonstrated in the initial post.

Discussion Status

There is ongoing clarification regarding unit conversions and the calculations involved. Some participants provide guidance on how to properly convert eV to joules and apply the relevant formulas, while others express concerns about the initial approach taken by the original poster.

Contextual Notes

Participants note the importance of understanding unit conversions and the definitions of power in the context of the problem. There is an implication that the original poster may not have fully engaged with the problem requirements.

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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