Chapter 13 Flashcards
What are black bodies?
Perfect absorbers of radiation
What is a photon?
A discrete packet of em radiation
Energy of atoms are multiples of Planck constant
What is the relationship between energy and frequency?
E=hf
E=hc/lamda
Energy is inversely proportional to wavelength
Also e=vq
What is the equation for power of a laser beam
Power= hf/t
What is the electron volt?
The work done by an electron of charge 1.6x10^-19 when accelerating between a pd of 1v
Ev=energy/1.6x10^-19
What is the golden leaf electroscope experiment
Touch the top plate with a negative electrode to charge the plate. The charge spreads to the stem and golden leaf, they are both negative so they repel
If you put a metal on the plate and shine uv light on it, the leaf falls back to the stem, proving that the stem has emitted electrons and lost its charge
What is the photoelectric effect
The emission of photoelectrons from the surface of a metal when it is illuminated by em radiation above the threshold frequency
What are the key observations of the photoelectric effect?
Frequency of radiation has to be above the threshold frequency for photoelectrons to be emitted
The emission is instantaneous
Increasing intensity only increases the number of photoelectrons emitted, not their energy as each electron only absorbs 1 photon
The value of kinetic energy increases with frequency, not intensity
Why does the photoelectric effect disobey wave theory?
Wave theory says that for any frequency of light, energy is proportional to the intensity of the beam
So electrons should gain energy from em waves gradually which it doesn’t do.
What if the frequency of a photon is below the threshold frequency?
Electron goes to a higher energy level but falls back down
What is the photon model?
A single electron on the surface of a metal absorbs the energy carried by a single photon
What is the work function?
The minimum amount of energy needed by an electron to escape a metals surface
ONLY FROM THE SURFACE
What happens to energy in excess of the work function?
It’s becomes the electrons kinetic energy
Hf= work function + ke max
What is threshold frequency?
The minimum frequency of em radiation that causes the emission of a photoelectron from the surface of a metal
Work function/h =f
What is KEmax?
The maximum kinetic energy of the emitted electron after the work function has been overcome
What does increasing intensity do?
It means more photons hit an area per unit time.
Which increases the number of interactions per second
So the number of photoelectrons emitted per second increases
It doesn’t effect the energy of anything
Why does the amount of energy required for an electron to emit change?
Work function is just for surface electrons. The deeper you go, the more attraction there is so more energy is required to free them.
The deeper you go, the less KEmax they have
What did De Broglie propose?
All matter has wave and particle like properties
What is wave particle duality?
A model used to describe how all matter has wave and particle like properties
What are matter waves?
Particles travelling like waves. All mass that is moving has wave like properties
It is a probability wave: the probability of finding a particle at a point is directly proportional to amplitude squared
What is the De Broglie relationship ?
Wavelength=h/p
Wavelength=h/MV
When can electrons diffract?
When they pass through gaps which are a similar order of magnitude to their wavelength.
Example of electrons acting as waves and as particles
They diffract: waves
They are affected by fields: particle
