Number of photons emitted by a laser

[songoku]

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

 

[Charles Link]

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.

 

[songoku]

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

 

[haruspex]

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.

 

[songoku]

Thank you very much for the help Charles Link and haruspex