C13. Quantum Flashcards
Covers all Quantum topics.
What is wave-particle duality?
Where light behaves with the properties of both a wave and a particle. It interacts with matter as a particle yet propagates through space as a wave.
How do electromagnetic waves carry energy?
In discrete packets ‘quanta’ called photons.
Define photon.
A massless quanta of electromagnetic energy.
What equation is used to quantise the energy of a photon?
E=hf
Why is energy not transferred continuously by an EM source but instead in discrete amounts?
EM waves consist of a stream of photons each containing individual packets/quanta of energy.
What does h represent in e=hf?
h represents Planck’s constant, 6.63*10^-34 Js
How do we use the equation e=hf to show wave-particle duality?
The equation links the properties of both a wave and a particle to the energy of photons.
Define the electronvolt.
1eV is the energy transferred when a single electron with elementary charge passes through a potential difference of 1V.
How to we convert from Joules to eV?
Divide the energy transferred in Joules by elementary charge.
What equation can we use to show the gain in kinetic energy due to an electron accelerating through a p.d.?
eV=1/2mv^2 (note this looks like the kinetic energy formula, with the result in Joules converted to eV).
How can we rearrange e=hf with the wave equation?
We can say that also e=hc/(lambda)
What evidence do we have for light acting as a particle?
The photoelectric effect.
What evidence do we have for light acting as a wave?
Young’s double slit experiment.
Define the photoelectric effect.
The emission of electrons when a metallic surface (containing many free electrons) absorbs electromagnetic radiation.
Give a name for electrons released as a result of the photoelectric effect.
Photoelectrons.
How did Heinrich Hertz discover photoelectric emission?
When UV light was shone onto a zinc plate electrode, electrons were emitted, causing a spark be produced more easily.
How does the gold leaf electroscope experiment work?
- A top plate is charged and a negative charge spreads through the gold leaf.
- This causes the gold leaf to rise and stay in place.
- When a source of UV is pointed at the zinc plat electrons are emitted.
- The leaf now falls slowly as the negative charge is depleted as electrons are released.
Why is the emission of photoelectrons instantaneous?
Only one photon interacts with one electron to reach a sufficient energy level for the electron to release - the energy does not accumulate but is rather provided in a one-to-one interaction.
Why are photoelectrons only released if incident EM radiation exceeds threshold frequency, regardless of intensity.
A single photon transfers its quanta of energy to a single electron in a one-to-one interaction - the number of photons (intensity) does not matter.
Why does intensity only affect the number of electrons emitted?
Photons and electrons interact on a one-to-one basis; one photon transfers all of its energy to one electron. Increasing intensity will only increase the rate of this energy transfer and therefore the number of electrons released at a given moment.
What is the work function of a metal?
The minimum energy required for an electron to be freed by a metal due to an incident photon.
What is the photoelectric equation?
Ek(max)=hf-hf0
- where hf0 is the work function
Why is the photoelectric equation a restatement of the conservation of energy?
Any energy transferred to a given electron due to an incident photon exceeding its threshold frequency is transferred fully to its kinetic store, since energy can never be created nor destroyed.
How does frequency affect the kinetic energy of an electron?
Once the threshold frequency is exceeded, as frequency increases, kinetic energy increases.
