C13 - Quantum Physics Flashcards
Who suggested the photon theory?
Einstein who used Planck’s theory of quanta.
What’s a photon?
A quantum of electromagnetic energy.
Light and all other forms of electromagnetic radiation is emitted in brief ‘bursts’ or ‘packets’ of energy.
These packets of electromagnetic energy are now called PHOTONS and they travel in a straight line in one direction.
When an atom emits a photon, its energy changes by an amount equal to the energy of the emitted photon.
What is an electron volt?
An eV is the energy transferred to or from an electron when it moves through a potential difference of 1V.
What is the work function?
The minimum energy needed to remove a single electron from the surface of a particular metal, measured in Joules.
What is the photoelectric effect?
The omission of photo electrons from the metal surface when electromagnetic radiation above the threshold frequency is incident on the metal.
What is the threshold frequency?
The minimum frequency of the electromagnetic radiation that will cause the omission of an electron from the surface of a particular metal, measured in hertz.
What are photoelectrons?
Electrons emitted from the surface of the metal by the photoelectric effect.
How can the photoelectric effect be demonstrated?
By using a gold leaf electroscope.
Charge the electroscope by briefly touching the top zinc plate with the negative electrode from a power supply or charged plastic rod.
Any charge developed on the plate at the top of the electroscope spreads to the stem and the gold leaf.
As both the stem and leaf have the same charge, they repel each other and the leaf lifts away from the stem.
Should of zinc plate be used, shining UV radiation onto the surface will cause the lift to fall slowly back towards the stem.
This shows that the electroscope has lost its negative charge as the radiation has caused free electrons to be omitted from the zinc, known as photoelectrons.
What occurs if incident radiation is above the threshold frequency during the photoelectric effect?
The emission of photoelectrons will be instantaneous.
Not a single electron will be emitted if the frequency is below the threshold frequency.
How does intensity affect the photoelectric effect?
Increasing the intensity (i.e. brightness) of the radiation incident on a metal surface increases the NUMBER OF ELECTRONS EMITTED PER SECOND.
This is because more photons hit the metal per second and each photon delivers energy to a single electron in a one-to-one interaction.
It does not increase the maximum kinetic energy of the photoelectrons; this can only be increased by increasing the frequency of radiation.
How does conservation of energy relate to the photoelectric effect?
The energy from a photon is able to free a single electron from the surface of the metal in a one-to-one interaction.
Any remainder is transferred into kinetic energy of the photoelectron.
Energy of a single photon =
The minimum energy required to free a single electron from the metal surface (work function) + the maximum kinetic energy of the emitted electron.
How can maximum kinetic energy of photoelectrons be increased?
By increasing the frequency of the incident radiation.
What affects the amount of energy needed for an electron from the metal?
Their relative position from the surface of the metal.
What does the X and Y intercept and gradient of a kinetic energy against incident frequency graph indicate?
X intercept - incident frequency
Y intercept - work function
Gradient - Planck’s constant
What is wave particle duality?
Theory that states that matter has both particle and wave properties and also electromagnetic radiation has wave and particulate (photon) nature.
(Suggested by De Broglie)
