Section 2: Electromagnetic Radiation and Quantum Phenomena Flashcards
Describe what is meant by the ‘photoelectric effect’.
Where electrons are emitted from the surface of a metal when a light of a high enough frequency is shone onto it
Describe what will happen to the electrons emitted by a metal if the intensity of the light shining on it is increased.
More electrons will be emitted, but their maximum kinetic energy will remain the same
What equation would you use to calculate the energy of a photon when given frequency of the light?
E=hf
Explain what happens UV radiation is incident on a negatively charged zinc plate which is attached to an electroscope?
The gold leaf will be angles upwards to begin with, as it is repelled from the negatively charged metal. The UV radiation releases electrons from the zinc plate removing the negative charge from the zinc plate. The gold leaf will then fall as the repulsion between the metal and the plate is reduced.
Explain why there is a threshold frequency below which no electrons will be emitted by a metal.
Before an electron can be emitted by a metal, it needs enough energy to break the bonds holding it there. This means there is a minimum amount of energy an electron needs before it can escape the metal surface. The threshold frequency is the minimum frequency of light that has photons with this energy.
Explain why electrons have a maximum possible kinetic energy.
The maximum amount of energy that can be transferred to an electron is the energy of one photon minus the work function of the metal.
Give the the photoelectric equation.
hf= work function +Ek(max)
What is an electron volt?
The kinetic energy carried by an electron after it’s been accelerated from rest through a p.d. of 1 volt
Why can photons emitted as an electron moves to a lower energy level in an atom only take an allowed value?
The transitions between energy levels that the electrons make are between definite energy levels, so the energy levels each photon emitted can only take a certain allowed value
What is the ionisation energy of an atom?
The energy needed to remove an electron from the ground state of an atom
In a fluorescent tube, a high voltage is applied across a mercury vapour. Explain how a fluorescent tube emits light.
Fast-moving free electrons that are accelerated by the voltage across the tube ionise some mercury atoms, producing more free electrons. These collide with the electrons of other mercury atoms. These collisions transfer energy to the electrons and excite them to a higher energy level. When these electrons return to their ground states, they lose energy by emitting photons of ultraviolet light. A phosphorous coating on the inside of the tube absorbs these photons, exciting electrons in the coating to much higher levels. These electrons then fall down to ground state and emit lower energy photons in the visible light range
What causes the pattern of lines seen in line emission spectra and line absorption spectra?
Photons of particular frequencies being absorbed or emitted by atoms. The frequencies correspond to the differences in energy between the discrete energy levels in atoms
Describe what is meant by wave-particle duality .
All particles have both particle and wave properties. Waves can also show particle properties
Name two effects that show electromagnetic waves have both waves and particle properties.
Diffraction and the photoelectric effect
What phenomenon shows that electrons have wave-like properties?
Electron diffraction
