3.2- MORE ABOUT PHOTOELECTRICITY Flashcards
What did Max Plank suggest at the end of the 19th century?
energy of each vibrating atom is quantised
What does quantised mean?
only certain levels of energy are allowed
What did Max Plank say about energy?
energy could only be in multiples of a basic amount, or quantum, hf
What did Max Plank imagine each energy level to be like?
rungs of a ladder, with each atom absorbing or emitting radiation when it moved up or down a level
What does the average kinetic energy of a conduction electron depend on?
temperature of the metal
In what order it the work function of a metal?
10^-19
Whats happens to the K.E. of an electron when it absorbs a photon?
its K.E. increases by an amount equal to the energy of the photon
What can happen if the energy of a photon absorbed by an electron exceeds the work function?
conduction electron can leave the metal
What happens when an electron absorbs a photon but it does not leave the metal?
it collided repeatedly with other electrons and positive ions, and it quickly loses its extra K.E.
What is a vacuum photocell?
glass tube that contains a metal plate (photocathode), and a smaller metal electrode (anode)
What happens when a light of frequency greater than the threshold frequency is for the metal is directed at the photocathode of a vacuum photocell?
electrons are emitted from the cathode and are attracted to the anode
What can the microammeter in the circuit of a vacuum photocell be used to do?
used to measure the photoelectric current
What is the current recorded from the microammeter in the circuit of a vacuum photocell proportional to?
number of electrons per second that transfer from the cathode to the anode
What is the equation for the number of photoelectrons per second that transfer from the cathode to the anode? (vacuum photocell)
I/e
I- photoelectric current
e- charge of the electron
What is the photoelectric current proportional to in a vacuum photocell?
intensity of the light incident on the cathode
What is light intensity a measure of?
energy per second carried by the incident light
What is the energy per second carried by the incident light proportional to? (vacuum photocell)
proportional to the number of photons per second incident on the cathode
What is the number of photoelectrons emitter per second proportional to?
intensity of the incident light
Why is the number of photoelectrons emitter per second proportional to the intensity of the incident light?
each photoelectron must have absorbed one photon to escape from the metal surface
What does the intensity of the incident light not affect?
the maximum K.E. of a photoelectron
Why does the intensity of the incident light no affect the maximum K.E. of a photoelectron?
no matter how intense the incident light is, the energy gained by a photoelectron is due to the absorption of one photon only
How can the maximum K.E. of the photoelectrons emitted for a given frequency of light be measured?
using a photocell
On a graph what is the kinetic energy?
y
On a graph what is the frequency?
x
