Number of photons emitted by a laser

In summary, the conversation is about converting 5 eV to joules and realizing that a watt is one joule per second. The correct conversion is found to be 5 eV = 8 × 10^(-19) joules, and n/t is calculated to be 1.25 × 10^16. The conversation also addresses the importance of putting effort into solving problems and not simply asking for the answer.
  • #1
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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  • #2
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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  • #3
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
 
  • #4
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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  • #5
Thank you very much for the help Charles Link and haruspex
 

1. How is the number of photons emitted by a laser determined?

The number of photons emitted by a laser is determined by the power of the laser and the frequency of the light it produces. This can be calculated using the formula: number of photons = power of laser / energy of one photon.

2. Does the type of laser affect the number of photons emitted?

Yes, the type of laser can affect the number of photons emitted. Different types of lasers have different power levels and produce light at different frequencies, which can impact the number of photons emitted.

3. Can the number of photons emitted by a laser be controlled?

Yes, the number of photons emitted by a laser can be controlled by adjusting the power and frequency of the laser. This can be done using various methods such as changing the current or voltage supplied to the laser or using specialized optics.

4. How does the number of photons emitted by a laser impact its performance?

The number of photons emitted by a laser directly affects its brightness and intensity. A higher number of photons can result in a more powerful and brighter laser beam, making it more suitable for certain applications such as cutting or welding.

5. Can the number of photons emitted by a laser be increased?

Yes, the number of photons emitted by a laser can be increased by increasing its power and/or frequency. However, this must be done within the limitations of the laser's design to prevent damage or malfunction.

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