# Photons emitted per sec.

XTEND

## Homework Statement

An LED emits a light beam with a power of 10 mW. The wavelength of the light is 420 nm. How many 420nm photons are emitted per sec.?

## Homework Equations

E=hc/lamda is 2.95E-9

P/E= Photons emitted per sec.

(10*10E-3)(2.95E-9)=2.952E-11

## The Attempt at a Solution

2.95E-11 is wrong.

2.1E16 photons per/sec. is the answer

Homework Helper
Your value for E is wrong.

h=6.626068 × 10-34 m2kg/s

Last edited:
XTEND
okay.

(6.626x10E-34)(3.0x10E8)=1.9878E-25 / 420nm = 4.7328E-28

(10x10E-3) / (4.7328E-28) = 2.1129E25

This is still not 2.1E16

Homework Helper
okay.

(6.626x10E-34)(3.0x10E8)=1.9878E-25 / 420nm = 4.7328E-28

You forgot to convert nm to m.

Homework Helper
okay.

(6.626x10E-34)(3.0x10E8)=1.9878E-25 / 420nm = 4.7328E-28

(10x10E-3) / (4.7328E-28) = 2.1129E25

This is still not 2.1E16

Check over your exponents in the part in red, it is not E-28.

XTEND
1.9878E-25/4.2E-7 = 4.7328E-19

(10x10E-3) / (4.7328E-19) = 2.1E16

Thank You!