3.2 More about Photoelectricity Flashcards
Who suggested that the energy of each vibrating atom is quantise (only certain levels of energy are allowed)
A physicist called Max Plank
Motion of the conduction electrons in a metal
Move at random.
What does the average kinetic energy of a conduction electron depend on
The temperature of the metal
What is the work function of a metal
The minimum energy needed by a conduction electron to escape from the metal surface when the metal is at zero potential
What happens when a conduction electron absorbs a photon
Its kinetic energy increases by an amount equal to the energy of the photon
What happens if the energy of the photon exceeds the work function of the metal
The conduction electron can leave the metal
If the electron does not leave the metal, it collides repeatedly with other electrons and positive ions and it quickly loses its extra kinetic energy
What is a vacuum photocell
A glass tube that contains a metal plate, referred to as the photocathode and a smaller metal electrode referred to as the anode
What happens when light of a frequency greater than the threshold frequency for the metal is directed at the photocathode
Electrons are emitted from the cathode and are attracted to the anode
Microammeter in circuit can be used to measure the photoelectric current
What is the photoelectric current proportional to
The number of electrons per second that transfer from the cathode to the anode
The intensity of th e light incident on the cathode
For a photoelectric current I, the number of photoelectrons per second that transfer from the cathode to the anode =
I/e
Where e is the charge of the electron
What is the light intensity a measure of
The energy per second carried by the incident light which is proportional to the number of photons per second incident on the cathode.
Why is the light intensity proportional to the number of photons per second incident on the cathode
Because each photoelectron must have absorbed one photon to escape from the metal surface, the number of photoelectrons emitted per second is therefore proportional to the intensity of the incident light.
The intensity of the incident light ______ ______ affect the maximum kinetic energy of a photoelectron. No matter how intense the incident light is, the energy gained by a photoelectron is due to the ______ of one photon ______. Therefore, the maximum kinetic energy of a photoelectron is still given by ______
Does NOT
Absorption
ONLY
Ekmax = hf - φ
The maximum kinetic energy of the photoelectrons emitted for a given frequency of light is can be measured using a…
…photocell
What is the x intercept of a graph of EKmax against f
Equal to the threshold frequency
