# Photoelectric exp - calculate intensity of incident light

1. Oct 3, 2014

### desmond iking

1. The problem statement, all variables and given/known data
In an photoelectric effect experiment , a photoelectric current of 100µA is obtained when lights of 550nm is incident on metal cathode of surface area 1.0cm^2 .... calculate the intensity of the incident light. The ans is 2.26w/m^2

2. Relevant equations

3. The attempt at a solution

intensity= power /area
intensity= (voltage x current) /area
intensity= ( (hc/λ) x I ) / area
= (6.63x10^-34)(3x10^8)(100x10^-6) / (550x10^-9)(1.0x10^-4) = 3.61x10^-19 (W/m^2 )

why am i wrong?

2. Oct 4, 2014

### ehild

How is the photoelectric current related to the number of electrons ejected? What is the relation between the number of electrons ejected and the number of the incident photons?
If you check the unit of your result, it is not W/m2.

3. Oct 4, 2014

### desmond iking

can you please tell me what's the unit of my 3.61x10^-19 should be? i am confused now.

4. Oct 4, 2014

### ehild

The problem is not with the units. If you check the unit of your result and it is not what it should be then your solution is wrong. Your solution is wrong, as its dimension is not energy/(time area).
Read the first two sentences of my previous post.

ehild