PAG 6.1 - Determining the Planck's Constant Flashcards
Describe the I-V characteristic of an LED
current can only pass through after threshold voltage
What is threshold voltage?
Minimum potential difference that needs to be across a diode before it allows a current to flow
How can threshold voltage be obtained scientifically?
Slowly increase PD across LED until it just begins to emit light and current flows through
How can you determine the point at which the LED begins to glow more precisely?
LED can be viewed through matt black paper to help prevent external light interfering with your view
How could you vary the potential difference of LED without changing the power supply?
LED can be placed in a potential divider circuit with a rheostat.
Resistance of rheostat decreases, potential difference across LED increases
What device can be used to measure the potential difference across the LED?
Voltmeter connected in parallel to the LED
How can you obtain the energy of a photon from frequency?
E =hf
How can you obtain the energy of a photon from wavelength?
E = hc/λ
What is the minimum energy of an electron moving through a PD?
E = eV
What equation can be formed by equating the electron energy with photon energy?
eV = hc/λ
Is the λ ov a green photon larger or smaller than a red photon?
Red photons have larger λ than green photons, so smaller energy
How can the Planck constant be determined from a graph of threshold voltage against 1/λ
Gradient will be Vλ
Vλ = hc/e
Planck constant is given by e/c x gradient
How can percentage difference in your experimental value and accepted value be calculated?
(Yours - Accepted)/ accepted x 100
What safety precautions should be taken when carrying out this experiment?
Ensure that the currents do not exceed the current rating
Avoid touching any bare metal contacts since they may be hot
