Grade 12 definitions - physics
Photoelectric effect
Electromagnetic (EM) radiation - Waves consisting of oscillating electric (E) and magnetic (B)
fields.
The Photoelectric Effect - The process that occurs when light shines on a metal and electrons
are ejected/emitted.
Threshold frequency (fo ) - the minimum frequency of incident radiation at which electrons will
be emitted from a particular metal
- Each metal has its own threshold frequency, this can be used to identify the metal.
- The threshold frequency corresponds to a maximum wavelength (λo )
Work function (Wo ) - the minimum amount of energy needed to emit an electron from the
surface of a metal
Only the frequency affects the energy of incident radiation and therefore the kinetic energy of
the photoelectrons emitted.
Intensity affects the number of photons (pockets of light with a specific energy/frequency)
emitted and therefore the number of electrons emitted per unit time.
The ground state of an atom - is the lowest allowed energy state.
he excited state - When a valence electron gains energy
- It moves from the ground state to a higher energy level
Produce an absorption spectrum - When electrons move from the ground state to an excited
state, they absorb photons.
produce an emission spectrum - When the electrons return to the ground state, they emit
photons
Emission spectra are produced when light from a luminous source(e.g. the sun) is passed
through a prism or diffraction grating. Electrons in the luminous material emit photon when they
move from an excited state back to the ground state.
Line emission spectra consists of separate lines of different colours (frequencies) on a dark
background. They are produced by hot gases under low pressure or vaporising salts.
, Continuous spectra are emitted by hot dense substances. The atoms in these substances are
close together resulting in many transitions between energy levels and all frequencies are
emitted. E.g.the spectrum of the sun and incandescent lamp
Absorption Spectra - These are produced when white light shines through a cooler gas. The
gas absorbs those frequencies which it would normally emit. The photons absorbed raise
electrons to higher energy levels. Distinct dark lines appear in the normal continuous spectrum
Photoelectric effect
Electromagnetic (EM) radiation - Waves consisting of oscillating electric (E) and magnetic (B)
fields.
The Photoelectric Effect - The process that occurs when light shines on a metal and electrons
are ejected/emitted.
Threshold frequency (fo ) - the minimum frequency of incident radiation at which electrons will
be emitted from a particular metal
- Each metal has its own threshold frequency, this can be used to identify the metal.
- The threshold frequency corresponds to a maximum wavelength (λo )
Work function (Wo ) - the minimum amount of energy needed to emit an electron from the
surface of a metal
Only the frequency affects the energy of incident radiation and therefore the kinetic energy of
the photoelectrons emitted.
Intensity affects the number of photons (pockets of light with a specific energy/frequency)
emitted and therefore the number of electrons emitted per unit time.
The ground state of an atom - is the lowest allowed energy state.
he excited state - When a valence electron gains energy
- It moves from the ground state to a higher energy level
Produce an absorption spectrum - When electrons move from the ground state to an excited
state, they absorb photons.
produce an emission spectrum - When the electrons return to the ground state, they emit
photons
Emission spectra are produced when light from a luminous source(e.g. the sun) is passed
through a prism or diffraction grating. Electrons in the luminous material emit photon when they
move from an excited state back to the ground state.
Line emission spectra consists of separate lines of different colours (frequencies) on a dark
background. They are produced by hot gases under low pressure or vaporising salts.
, Continuous spectra are emitted by hot dense substances. The atoms in these substances are
close together resulting in many transitions between energy levels and all frequencies are
emitted. E.g.the spectrum of the sun and incandescent lamp
Absorption Spectra - These are produced when white light shines through a cooler gas. The
gas absorbs those frequencies which it would normally emit. The photons absorbed raise
electrons to higher energy levels. Distinct dark lines appear in the normal continuous spectrum
