# Photoelectric Effect - Variables

1. Jul 14, 2012

### Pinchy444

1. A scientist is investigating the effect of different types of radiation on the surface of a piece of Sodium metal. He uses a freshly cut surface on a Sodium plate.

2. a) Which of the variables is the dependent and independent variables?
b) Why must the surface of the Sodium metal be carefully prepared?

3. a) I assume that the independent variable is the frequency of the light being emitted and the dependent variable is the Stopping Voltage.
b) I believe that the metal should be prepared carefully so as to avoid any impurities being found on the metal hence effecting overall experimental results. Am I correct for both questions?

Any help will be appreciated.
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Jul 15, 2012

### ehild

Do not forget the threshold frequency as dependent variable.

Think of the chemical properties of sodium. It is very active, and it reacts easily by oxygen. If the surface layer is not removed before the experiment the photons interact with that layer first before reaching the sodium metal. Also the photoelectrons emitted can be trapped by the imperfections of the surface as you wrote and by the layer.

ehild

3. Jul 15, 2012

### Pinchy444

I have the independent variable as Frequency of light and dependent as Stopping Voltage. I don't understand how the threshold frequency is the dependent variable? Could you please explain further?

Appreciate it,

4. Jul 15, 2012

### ehild

In the experiment, you measure current of the photoelectrons. Starting from law frequency light and increasing frequency, you get zero current below a specific frequency - the threshold frequency. That is, when the energy of the photons is equal to the work function.
When you detect current at all, you can change the voltage (you can consider voltage also an independent variable) and detect the stopping voltage when the photocurrent becomes zero. So the primary dependent variable is the current of photoelectrons.

ehild

5. Jul 15, 2012

### Pinchy444

Awesome!

Appreciate the help.