Using LEDs to estimate Plank's constant (4.3)

Question 1

What equipment do you need for the plank’s constant LED experiment?

Answer 1

LEDs, voltmeter, 6V battery, variable resistor

Question 2

What is the graph for the Plank’s constant from LEDs experiment?

Answer 2

Threshold voltage, V - y-axis
against
1/wavelength, 1/l - x-axis

Question 3

How do you find plank’s constant from the V - 1/l graph from the LED experiment?

Answer 3

You should get a straight line graph with a gradient of hc/e, which you can use to find the value of h

Question 4

How do you carry out the plank’s constant from LEDs experiment?

Answer 4

1) Connect an LED of known wavelength to the circuit [you drew above]
2) Starting with no current going through the circuit, adjust the variable resistor until the led just starts to light up
3) Record the voltage across the LED and the wavelength it emits
4) Repeat with various LEDs
5) Plot a graph of voltage against 1/wavelength
6) The gradient is hc/l