Module 4 - Section 3 (Quantum Physics and Particle Physics) Flashcards
What is one photon?
One photon is one quantum of energy of electromagnetic radiation.
What is the interaction rule with a photon?
It is a one to one interaction when the photons interact with one partivle giving all or none of the energy.
What is the equation for the energy of one photon?
E = hf
-h = planks constant
-f = frequency of light
Why are electron volts used?
They are a more appropriate and suitible measure to measure the energies involved in a reaction.
What is the equation for frequency?
f = c/ λ
-c = speed of light
-λ = wavelength
What is another equation for the energy of one photon?
E = hc/λ
What is the threshold votage of an LED?
The threshold voltage is the minimum voltage needed for the current to pass across the component. This is the voltage needed to give to the electrons the same energy as a photon that is emmitted.
What is the conversion between eV and J.
1 eV = 1.6x10^-19 J
–>eV - J (times by charge of electron)
–>J - eV (divide by charge of electron)
How do you find the Planks Constant (Practical)
Set up a circuit with:
-voltmeter
-LED’s of different colours
-variable resistor
-ammeter
-power pack
Method
1. Start with the variable resistor at its maximum resistance so no current can flow.
2. Adjust the resistance so that the light just turns on hense the current just beggining to flow.
3. Record the threshold voltage (this is the voltage that just allows the LED to light up).
4. Also record the wavelegth of the colour of light that is being used.
5. Turn power pack of to allow the circuit to cool and then repeat with a different colour LED.
Then sub into the the equation:
E = hc/λ
And rearange to have h as the subjuct to find planks constant:
h = eV x λ / C
-where e is the charge of one electron
-V is the threshold voltage
What is the photoelectric effect?
The photoelectric effect is the emission of electrons (normally from a metal) caused by electromagnetic radiation (light).
What is the Work Function?
The minimum amount of energy needed for the bonds to break between the electrons and the surface of the metal in order for the electron to be emitted as a photoelectron.
What is an experiment that could demonstrate the photoelectric effect?
GOLD LEAF ELECTROSCOPE EXPERIMENT
1. A zinc plate is attached to the top of an electroscope and it is negatively charged.
2. The two gold leafs in the electroscope repel as like charges repel each other.
3. Using a UV lamp Ultra violet light is shone onto the zinc plate.
4. The packets of energy from this light (photons) causes electrons to be lost from the zinc plate via the photoelectric effect.
5. As the zinc plate looses its charge, so does the gold leafs, causing them to come back down and be together.
When are photoelectrons not emitted?
They are not emmited when the the incident radiation has a frequncy below the threshold frequency.
How does the kinetic energy of photoelectrons vary?
The kinetic energy of the photoelectrons varies with the initial frequnecy of the radiation.
When the threshold frequency is just met what is the kinetic energy?
0
What changes the amount of photoelectrons emitted per second?
The Intensity of the radiation
Why cant wave theory explain the threshold frequency?
In wave theory, even when the threshold theory is not met and is under, the electrons should gradually gain energy untill the threshold frequency is met. The particle theory is suggested her as electrons can only be released when the threshold frequncy is met or over.
What is the step by step guide to the PHOTOELECTRIC EFFECT?
- EM Radiation hits a metals surface
- The surface is bombared by photons.
- The photons then react with any free electron via a one to one reaction where 1 photon reacts with 1 electrons to release one photoelectron.
- The photoelectron gains all of the energy equal to hf
- This supports the particle like nature of EM radiation.
What is Wave Particle Duality?
When Light behaves as both a particle and a wave. A paricle due to the photoelectic effect and the gold leaf experiment and then a wave in the electron diffraction through a slit.
When Does light behave like a wave?
Light behaves like a wave in diffraction where a light been is shone through a slit and it spreads out- if it was a particle it would either pass through or not and would not spread out and carry a straight course.
When do electrons fit the wave theory?
When electrons are accelerated towards a thin graphite sheet they then pass through the Carbon atoms and then diffract as waves, producing rings on the screen at the end of the accelerator.
When do electrons fit the particle theory?
The photoelectric effect .
What is the de Broglie equation?
λ= h/p
h- planks constant
p- momentum (mass x velocity)
What is an isotope?
Elements which have the same number of protons but a different number of neutrons.
Therefore, they have the same atomic number but a different mass number.
