11 Quantum Physics Flashcards
What do electrons behave like?
Particles
What was the first particle accelerator?
The electron discharge tube.
What does an electron discharge tube accelerate?
electrons.
Who used an electron discharge tube?
J.J. Thompson
Why did J.J. Thompson use an electron discharge tube?
To show the existence of the electron.
What is the charge of an electron?
1.6 × 10‐¹⁹ C
What is the mass of an electron?
9.1 × 10‐³¹ kg.
What does an electron discharge tube do?
Fires electrons like bullets. The electron beam is made visible by hitting a zinc sulphide screen. A magnetic can be used to deflect the electrons and hence correctly predict the deflection of the beam by treating the electron as a little chunk of mass.
What equation connects voltage, work done and charge?
V = W/Q
How do you apply the work energy principle to an electron discharge tube?
The work done in accelerating the electron is equal to the energy transfered to the electron.
What is the energy transferred to an electron in the form of?
Kinetic energy.
What is the speed of light?
3×10⁸ m s‐¹
What does light behave like?
Waves.
What does light diffract to form?
Interference fringes.
How does light show wave behaviour?
•Double slit interference using a laser shows light diffracting to produce interference fringes meaning the light is showing wave behaviour.
•light can produce rings of constructive and destructive interference when viewed through a microscope coated with lycopodium powder. Viewing light from sodium, radium and helium lamps produces different colours of ringed interference patterns.
What is wave-particle duality?
Beams of electrons were shown to behave like waves, and light could behave like particles.
Until the 20th century, what did experimental evidence show that electrons and light behave like?
•electrons behave like particles.
•light behaves like wave
This is now not always the case.
What is a gold leaf electroscope for?
Showing charge.
How does a gold leaf eletroscope work?
Electrons are scraped on to a zinc plate from a charged polythene rod. This causes the gold leaf inside the electroscope to rise. When photons of ultra-violet light are incident on the surface of the zinc plate, the gold leaf drops meaningnelectrons are being emitted from the zinc plate.
What colour is a sodium lamp?
Bright orange
What colour is a neon lamp?
Red
What happens if you shine a sodium or neon light onto a gold leaf electroscope?
Nothing
What happens if you shine a sodium lamp onto a gold leaf electroscope for a long period of time?
Nothing
Will an ultra-violet light being shined onto a gold leaf electroscope cause electrons to be ejected?
Yes
What is the photoelectric effect?
The emission of electrons from a metal surface when photons of light of a high enough frequency are incident upon the metal surface.
What is the symbol for threshold frequency?
f₀
When does emission of electrons only occur?
When the incident photon frequency is above a specific minimum frequency.
What is the minimum frequency that the incident photons frequency needs to be above for the emission of electrons to occur?
Threshhold frequency (f₀)
What is red light always less than?
The threshold frequency (f>f₀).
What is blue light always more than?
The threshold frequency (f<f₀).
What is the threshold frequency (f₀)?
The minimum photon frequency which will overcome the work function and hence cause the emission of electrons.
Does the emission of electrons always occur immediately if the frequency of the light is greater than the threshold frequency?
Yes, even if the light is very dim.
What did Planck work out (photons)?
In some experiments light behaves like particles, described as quanta which he called photons.
What did Einstein say can only be explained using the idea of photons?
The photoelectric effect.
In the photon energy equation what is ‘h’?
Planck’s constant.
What does photon energy depend on?
Frequency (or wavelength) of the light.
What is a photon?
A quantum of electromagnetic energy.
What did Eistein visualise when an electron absorbed a photon?
The electrons energy increased by an amount equal to the energy of the photon. This extra energy might be enough for the electron to escape from the metal
What are Einsteins 6 explanations of the photoelectric effect?
Why do electrons on the metal surface need the least energy?
To escape and so are ejected with the most kinetic energy.
What are electrons deeper inside the metal ejected with?
A range of lower kinetic energy.
What is the definition for work function (Φ)?
The lowest photon energy needed to extract an electron from the surface of a particular metal.
What is work function (Φ) measured in?
Joules
What is the symbol for work function?
Φ
What did Einstein realise that the work function (Φ) must equal ?
The energy of the threshold frequency photon.
Φ = hf₀.
What equation links energy, planks constant and threshold frequency?
E = hf₀
If the energy of the photon that the electron absorbs is bigger than the energy needed for the electron to escape from the metal, what does the energy left over (once the electron has escaped) appear as?
Kinetic energy of the electron.
What equation summarised Einsteins ideas?
Energy of the photon absorbed by the electron = energy needed to remove the elctron from the metal + left over kinetic energy.
Which electrons will have the most kinetic energy?
Those that are easiest to extract from the metal.
Which electrons will have the least kinetic energy?
The electrons below the surface that will need more energy to escape from the metal.
What is E kmax?
Electrons are ejected from the metal witha a range of energies from zero up to a maximum value.
What is the equation for a photon?
Minimum energy to eject an electron + maximum energy to eject an electron.
What is planks constant?
6.63 × 10‐³⁴ J s
What is the other unit for energy?
Electron volt.
How many joules is one electron volt equal to?
1.6 × 10‐¹⁹ J.
What is the conversion from electron volts to joules the same as?
The charge of an electron.
on the data sheet
What are photoelectrons?
Electrons emitted from a metal due to light shining on the metal.
no different to other electrons.
