2.2 Electromagnetic radiation and quantum phenomena Flashcards
Are electromagnetic waves transverse or
longitudinal?
Transverse.
What phenomenon can be used to show
that light behaves as a particle?
The photoelectric effect
Describe the photoelectric effect.
When light above a particular frequency is shone
on metal, electrons are released - these released
electrons are “photoelectrons”.
What is the threshold frequency?
The minimum frequency of light required for an
electron to be emitted.
What equation is used to determine the energy of a photon?
E = hf = hc/𝜆
Energy = Planck’s constant x frequency
Energy = (PC x 3 x 10^8) / wavelength
Why does a photon need to have a
minimum frequency in order to liberate
an electron?
The energy of the photon is determined by its
frequency, the photon’s energy must be greater than
the work function (energy needed to break bonds
holding the electron) in order for an electron to be
emitted.
If a photon has a frequency higher than the threshold frequency, what would occur?
The electron will be liberated and the remaining
energy is the kinetic energy of the electron.
If light is incident on a metal and
photoelectric emission does NOT occur,
what is the effect of increasing light
intensity?
● If it is more intense then there would be more photons
incident on the metal each second
● However each photon still carries the same amount of
energy as before
● Therefore it still does not contain enough energy to
liberate an electron
● No effect
What is the photoelectric equation?
Planck’s constant x frequency = work function +
maximum kinetic energy of the photoelectrons
Define the work function.
The energy required by an electron to overcome
the metallic bond holding it in the metal.
What is an electron volt?
The kinetic energy of an electron that has been
accelerated from rest through a potential difference of 1V.
How does a fluorescent tube work?
● High voltage applied across mercury vapour accelerates fast
moving free electrons which collide with the mercury atoms.
● Mercury electrons are excited and then return to the ground
state, releasing a UV photon.
● The tube’s phosphorus coating absorbs the UV photons and its
electrons are excited, they cascade down the energy levels and
emit visible light photons
What can be used as evidence for the discrete energy levels in atoms?
Line emission and absorption spectra as the lines appear at
discrete points which show where a light photon of specific
frequency and wavelength has been absorbed or emitted, this
shows electrons can only absorb an exact amount of energy
to be excited to the next discrete energy level.
What is wave particle duality?
All particles have both particle and wave
properties, waves can have particle properties
e.g. light acts as a particle in the photoelectric
effect and as a wave when it is diffracted.
