Particle physics

These cards relate to the particle physics unit for AQA physics A.

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Photoelectric effect

A photon is emmited, its energy=hf. One photon will interact with one electron on the surface of teh metal. if there is enough energy to overcome the work function of teh metal an electron will be emmited, any extra energy energy will be kinetic energy of the electron when it leaves.

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Rutherford's scattering

The foil should be thin otherwise

α particles may be absorbed/so α particles can penetrate the foil, α particles must only be scattered once.

The beam should be narrow to have definite location where the scattering takes place

so the scattering angle can be determined accurately.

Evidnece that most of the mass is in thenucleus of the atom is backscattering/scattering angles greater than 90º occurs because α particles must collide with a target (much) more massive then themselves

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How does mercury vapour and coating of the inner t

Mercury vapour at low pressure is conducting. Atoms of mercury are excited by electron impact. producing mainly UV raidation. Which is absorbed and excites the coating. Which upon relaxing produces visible light. Electrons cascade down energy levels.

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Duality of electrons.

This is when an electron behaves as a awve and a particle. An example of it behaving as a wave is diffraction, and an example of it behaving as a particle is in the photoelectric effect.

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Principle features of a gas from their line spectr

Photns have definite wavelengths/frequency. So photons have discrete energies. Photons are emitted when electrons move down from one level to another. The energy gaps between energy levels are fixed.

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What happens if teh wavelength stays the same but

The maximum kinetic energy depends upon the frequency and energy of the incident radiation. Maximum kinetic energy remains unchanged. Doubling the intensity doubles the number of photoelectrons per second. One photon interacts with one electron.

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Critical angle

The angle of incidence at the more dense-less dense boundary. Producing an angle of refraction of 90 degrees.

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What would happen if the fibre was surrounded by g

The ray would leave the core, bending away from the normal, increase in critical angle, light speed increase.

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Effect of increasing the intensity of UV light

The number of photoelectrons emitted per second will be increased

as the number of incident photons per second is increased but the maximum kinetic energy of the photoelectrons will remain constanta photon gives up all its energy in one collision.

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Describe what happens to an atom in the ground sta

an electron is excited/promoted to a higher level/orbit

reason for excitation: e.g. electron impact/light/energy externally applied

electron relaxes/de-excited/falls back emitting a photon/em radiation

wavelength depends on the energy change

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Pair production

γ photon or high energy photon/kinetic energy

converted to a particle and its antiparticle

p + p or e− + e+

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Why does the kinetic energy of light have a maximu

incident photon energy is fixed

[or photoelectron receives a fixed amount of energy]

photon loses all its energy in a single interaction

electron can lose various amounts of energy to escape from the metal

electrons have a maximum energy = photon energy − work function

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What role does an exchange particle play in an int

transfers energy, transfers momentum, transfers force, sometimes transfers charge.

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Why is there a minimum energy in pair production?

The gamma ray must provide enough energy to compensate the mass of the two products. Any extra energy will provide the products with kinetic energy.

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Intensity of light is reduced in the photoelectric

Then there will be less photonelectrons per second emitted. The enrgy levels will remain the same also the speed at which they leave the atom remains the same as these are fixed. One photn interacts with one electron.

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Why are no photoelectrons released when theblue fi

There needs to e enough energy to overcome the work function of the metal. Photon of red light has less energy than photon of blue light. energy is proportional to frequency, E=hf.

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