Definitons Electrons, waves and photons Flashcards
coulomb
the charge transferred by a 1 ampere current in one second
volt
1 joule per coulomb
ohm
the resistance when 1 volt of potential difference produces 1 ampere of current
kilowatt-hour (kW h)
the energy transferred by a 1 kW device in a time of 1 hour
electronvolt (eV)
the energy transferred by an electron travelling through a potential difference of 1 V
electric current
flow of charge per unit time
number density
the number of charged particles per unit volume
resistance
p.d/current
resistivity
(Resistance x cross sectional area) / length
power
work done per unit time
potential difference
energy transferred per unit charge from electrical energy into other forms (e.g. light or heat)
electromotive force
energy transferred per unit charge into electrical energy from other forms (e.g. chemical)
internal resistance
Some energy is lost as heat in the battery; it behaves as if it has an internal resistance
terminal p.d.
the potential difference measured across the terminals of an e.m.f. source
displacement
distance moved from equilibrium of a point on a wave
amplitude
maximum displacement
wavelength
the distance between two adjacent peaks and troughs
period
the time taken for one complete oscillation of a particle
phase difference
the fraction of a cycle (measured in degrees) between the oscillations of two particles
path difference
the difference in the distances travelled by two waves from coherent sources at a particular point
frequency
number of wavelengths passing a point per unit time
speed of a wave
distance travelled by the wave per unit time
work function
minimum energy to release an electron from the surface of a metal
threshold frequency
the minimum frequency of electromagnetic radiation that will release an electron from the surface of a metal
Conventional current
moves from positive to negative terminals of battery
electron flow
moves from negative to positive terminals of battery
Kirchoff’s first law
sum of current into a junction equals the sum of current out; charge is conserved
Kirchoff’s second law
sum of e.m.f.s around a loop = sum of p.d.s around the same loop; energy is conserved
mean drift velocity
the average speed of charged particles along the length of a conductor
Ohm’s law
for a metallic conductor at a constant temperature, the voltage is proportional to the current
progressive wave
Waves that transfer energy away from a source without transfering material as a result of osicllations.
stationary wave
superposition of 2 progressive waves with the same wavelength, moving in opposite directions
longitudinal wave
Osscilation moving paralel to the direction the wave is travelling in
transverse wave
Osscilation moving perpendicular to the direction the wave is travelling in
refraction
the change in direction of a wave as it crosses an interface between two materials where its speed changes
diffraction
wavefronts spread out after passing through a gap or around an obstacle
intensity
the rate of flow of energy per unit area at right angles to the direction of travel of the wave. Measured in Wm^-3
plane polarised wave
a transverse wave that vibrates in one plane only
superposition
When 2 or more waves of the same type meet, the resultant wave can be found by adding the displacments of the individual waves
interference
Superposition of coherent waves so there’s a change in overall displacement
constructive interference
when two waves reinforce to give increased amplitude
destructive interference
when two waves cancel to give reduced amplitude
coherence
constant phase difference between waves
node
where the amplitude is always zero
antinodes
where the amplitude of the standing wave takes the maximum possible value
photon
a packet of energy
photoelectric effect
instantaneous emission of electrons from a metal surface when photons are incident on the surface
