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Flashcards in Quantum Oddnes Deck (45)
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Show that an electron can be a wave?

It can diffract.


What is wave particle duality?

An object displaying both wavelike and particle properties.


Show that an electron can be a particle.

It can collide with other electrons. If a current is passed through a gas the electrons of the electricity will collide with electrons of the atom, removing them and ionising the atom.


Show that a photon can be a particle.

The photoelectric effect.


Show that a photon can be a wave?

Is can diffract.


What has the photoelectric effect have nothing to do with?

Energy levels.


Explain the basics of the photoelectric effect.

A photon hits a de-localised electron in a piece of metal. The electron will absorb the energy of the photon meaning it is liberated. It can leave the metal.


How does the photoelectric effect show that light can be a particle ?

If it was just a wave, then energy from different waves could build up in the metal meaning any wavelength of light would cause the effect. It will work or is won't so the energy must come in photons or particles.


What will one photon react with in the photoelectric effect?

One electron.


How can the speed of a liberated photon be calculated?

Energy = 0.5mv²


What does Ø mean?

The work function.


Define the work function.

The minimum energy needed to liberate an electron from the surface of the metal.


Define threshold frequency.

The minimum frequency with which a photon has sufficient energy to over come the work function and liberate an electron from the surface of the metal. Below this frequency nothing is emitted.


Where is the work function shown on a graph?

It is the Y intercept


Where is the threshold frequency shown on a graph?

The X intercept.


What does the gradient on a photoelectric graph show?

The plank constant.


What is the symbol of the threshold frequency ?



On a photoelectric graph, what is on the Y axis?

Maximum kinetic energy.


On a photoelectric graph, what is on the X axis?



What is the ground state ?

The energy level of an atom where the electron has the lowest possible energy.


What is the photoelectric formula re-arranged to be a graph equation?

E"k" = hf-Ø
Y = mx+c


Why are electrons only emitted from a piece of metal when the light on it is of a certain frequency?

The energy of each photon of light will increase with the frequency.
The electrons of the metal need a minimum amount of energy to leave the metal. This energy is equal to the work function.
Thus the light frequency must be high enough so that the energy produced by a photon is enough to move an electron.


Why is the particle theory of light better at explaining the photoelectric effect than a wave theory?

The energy of a photon increases with the frequency.
Electrons need a minimum amount of energy to leave the metal.
This amount of energy is equal to the work function.
This suggests electrons are given energy in one discrete event.
Thus light energy is concentrated (into photons)
Electrons don't build up energy over time. Photoelectricity occurs immediately after light falls on it.


Explain why when light is emitted on metal, why electrons are emitted and why the kinetic energy of the electrons varies up to a certain value.

Light is made of electrons whose energy depends on the frequency of the light.
Electrons on or near the surface of the metal can gain the energy of a photon when they meet.
Each electron needs a minimum amount of energy to leave and this is the work function.
This means the maximum kinetic energy of electrons emitted is the energy of a photon minus the work function.
Give reasons why electrons have different energies.


What are electrons naturally inclined to do in terms to energy levels?

Go to the lowest energy level it can. It does this by emitting a photon.


What happens if an electron comes into contact with a photon which will give to enough energy to not fit in any energy state?

An electron must absorb all of the energy or none of the energy. Thus if the energy of a photon won't put it in an energy level, it won't absorb it.


What is the emission spectrum?

The emission spectrum of a chemical element or chemical compound is the spectrum of frequencies of electromagnetic radiation emitted due to an atom or molecule making a transition from a high energy state to a lower energy state


Why are energy levels negative?

Because it is bound to the atom so you have to put energy into it to get it out.
0 is the largest energy level.


What would happen if a -4ev electron absorbs a 7ev photon?

It will have ionised the atom, left and have 3ev


What are the three main observations produced by doing experiments with the photoelectric effect?

No electrons are emitted if the light it below a certain frequency.
The energy of the emitted electrons varies up to a maximum. This maximum depends on the frequency of the light. It is unaffected by the intensity.
The number of photo electrons emitted is proportional to the intensity if the light.