# physics

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- Created by: DrewThorpe
- Created on: 04-05-16 12:35

photoelectric effect

The photoelectric effect occurs when light above a certain frequency (the threshold frequency) is shone on metals like zinc, this causes electrons to escape from the zinc. The escaping electrons are called photo electrons.

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photoelectric effect experiment

the frequency of the light needed to reach a particular minimum value for photoelectrons to start escaping the metal AND the maximum kinetic energy of the photoelectrons depended on the frequency of the light not the intensity of the light

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photoelectric effect experiment

The above two observation can only be explained if the electromagnetic waves are emitted in packets of energy (quanta) called photons, the photoelectric effect can only be explained by the particle behaviour of light.

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The photoelectric equation involves;

hf=(phi)+Ek h = the Plank constant 6.63 x 10-34 J s f = the frequency of the incident light in hertz (Hz) phi = the work function in joules (J) Ek = the maximum kinetic energy of the emitted electrons in joules (J)

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equation

The energy of a photon of light = hf and the work function (f)is the minimum energy required to remove an electron from the surface of the material.

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equation

So we can see from the equation above that if the light does not have a big enough frequency (f) so that the photon has enough energy to overcome the work function (f) then no photoelectrons will be emitted.

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graph

So plotting a graph of freq on the x-axis and maximum kinetic energy on the y-axis will give a straight line graph. Where the gradient is the Plank constant and the y intercept is the work function, the intercept on the x-axis is the threshold freq

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Excitation

the addition of a discrete amount of energy (called excitation energy) to a system—such as an atomic nucleus, an atom, or a molecule—that results in its alteration, ordinarily from the condition of lowest energy (ground state) to one of higher energy

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The electron volt (eV) is an amount of energy.

It is the amount of energy an electron would gain if it was accelerated through a potential difference of 1 volt. 1 eV = 1.6 x 10-19 joules (J) of energy

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In atoms electrons orbit the nucleus.

There are particular allowed orbits where electrons can exist without emitting energy. Electrons can pass between these energy levels. When electrons are given enough energy to move to higher energy levels they are in an excited state,excitation

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further excitation

If an electron gets enough energy to remove the electron to infinity this is called ionisation.

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Line Spectra

an emission spectrum consisting of separate isolated lines. an emission (of light, sound, or other radiation) composed of a number of discrete frequencies or energies

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Emission spectra

A diffraction grating and a spectrometer can be used to look at the emission spectrum from a light source. If all possible wavelengths of light are present it would look like a continuous spectrum of colours.

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Emission spectra

Each line in the emission spectrum corresponds to an electron moving from a higher energy level to a lower energy level. To do this it emits photon of light the energy of the photon of light is equal to the difference in the energy of the two energy

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hf= E1-E2

h = the Plank constant 6.63 x 10-34 J s f = the frequency of the photon in hertz (Hz) hf = the energy of the photon in joules (J) E1 and E2 is the energy of energy level 1 and 2 in joules (J)

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Absorption spectra

When white light passes through a gas the gas absorbs particular wavelengths of light. This effect can be seen in light from the sun which initially seems like a conscious spectrum but an closer inspection it can be seen to contain dark lines.

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Wave-particle Duality

Sometimes light behaves like a wave and sometimes light behaves like a particle.Diffraction – can be explained by considering light to be a wave. Photoelectric effect – can be explained by considering light to be a particle. we use this with light

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Momentum

The momentum of a particle can be calculated by multiplying it’s mass in kilograms (kg) by it’s velocity in metres per secons (m s-1). Momentum is measured in kilogram metres per second ( kg m s-1 ) momentum = mv

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De Broglie wavelength

De Broglie wavelength

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wavelength= h/mv

l = the de Broglie wavlength of the particle in metres (m) h = the Plank constant 6.63 x 10-34 J s m = mass of the particle in kilograms (kg) v = velocity of the particle in metres per second (m s-1)

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## Other cards in this set

### Card 2

#### Front

photoelectric effect experiment

#### Back

the frequency of the light needed to reach a particular minimum value for photoelectrons to start escaping the metal AND the maximum kinetic energy of the photoelectrons depended on the frequency of the light not the intensity of the light

### Card 3

#### Front

photoelectric effect experiment

#### Back

### Card 4

#### Front

The photoelectric equation involves;

#### Back

### Card 5

#### Front

equation

#### Back

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