3.1- THE PHOTOELECTRIC EFFECT Flashcards
What do metals contain?
conduction electrons
What do conduction electrons do in metals?
move about freely inside the metal
What do the conduction electrons in metals collide with?
each other and with the positive ions of the metal
What did Heinrich Hertz discover?
how to produce and detect radio waves
What did Heinrich Hertz find when he discovered how to produce and detect radio waves?
sparks produced in his spark gap detector when radio waves were being transmitted were stronger when ultraviolet radiation was directed at the spark gap
What did further investigations on the effect of EM radiation show?
electrons are emitted from the surface of a metal when EM radiation above a certain frequency was directed at the metals
What is the term for when electrons are emitted from the surface of a metal when EM radiation above a certain frequency was directed at the metals
photoelectric effect
What observation were made following the observations from the photoelectric effect that were a major problem as they could not be explained using the idea that light is a wave? (3)
photoelectric emission of electrons from a metal surface does not take place if the frequency of the incident EM radiation is below a certain frequency
no. of electrons emitted per second proportional to intensity of incident radiation
photoelectric emission occurs without delay as soon as the incident radiation is directed at the surface
What is the threshold frequency?
minimum frequency of the incident electromagnetic radiation for photoelectric emission of electrons from a metal surface
What does the minimum frequency depend on?
type of metal
What must the wavelength of the incident light be like for photoelectric emission?
less than the maximum value equal to the speed of light divided by the threshold frequency
Provided, what is the number of electrons emitted per second proportional to the intensity of the incident radiation?
frequency is greater than the threshold frequency
Provided what, allows the photoelectric emission without delay as soon as the incident radiation is directed at the surface?
frequency of the radiation exceeds the threshold frequency
What can the wave theory not explain about the photoelectric effect?(2)
existence of threshold frequency
why photoelectric emission occurs without delay
What does the wave theory explain about the conduction electrons in photoelectric emission?
each conduction electron at the surface of a metal should gain some energy from the incoming waves, regardless of how many waves arrive each second
What did Einstein put forward in 1905?
photon theory of light
Why did Einstein put forward the photon theory of light in 1905?
to explain the photoelectric effect
What did Einstein assume about light when putting forward the photon theory of light?
assumed light is composed of wavepackets or photons
What is the energy of each photon?
hf
What did Einstein say to explain the photoelectric effect? (2)
when light incident on metal surface, an electron absorbs a single photon from the incident light so gains energy equal to hf
electron can leave metal surface if energy gained from single photon exceeds work function of metal. excess energy gained by photoelectron becomes its K.E
What is the definition of work function?
minimum energy needed by electron to escape from metal surface
How can electrons that escape from the metal plate be attracted back to it?
by giving the plate a sufficient positive charge
What is the definition of stopping potential?
minimum potential needed to stop photoelectric emission
What happens to the maximum kinetic energy of the emitted electron at stopping potential?
maximum K.E. of the emitted electron is reduced to zero
