physics flash cards
Electric current
Electric current is the net flow of any electrically charged particles
Electrons
Electtrons are the particles that there is a ‘netflow’ of when an electric current is flowing through a metal
Ions
Ions are teh particles that there is a ‘netflow’ of when an electric current is flowing through ann electrolyte
Coulomb
One coulomb is the charge moved when a current of on amp flows for one second of time through a point in a circuit
Kirchhoff’s first law
The sum of the currents entering any junction in a circuit is equal to the sum of currents leaving that same junction because of the conservation of charge
Mean drift velocity
Mean drift velocity is the average displacement per unit time with which charge carriers move in the direction of convectional current flow
Potential difference
Potential difference is energy transferred (to other forms) per unit charge
Volt
When 1J of energy is tranferred (to other forms) per Coulomb of charge, the p.d across 2 points is 1 Volt
Voltmeter
Are connected in parallel with the circuit. they have a high resistance so that they do not unduly disturb the circuit to be measureed
e.m.f
e.m.f is the electrical potential energy gained by charges, per unit charge, (across two points in a circuit).
Differences between e.m.f and p.d in terms of energy
e. m.f:work done on charges (charges gain electrical potential energy),across 2 points,per unit charge
p. d:work done by charges (charges transfer electrical potential energy to other forms), across 2 points, per unit charge
Resistance
Resistance is ratio of p.d across a component to the current through the component
Ohm
1 Ohm is defined as the resistance of a component when a constant p.d of 1Volt, applied across the component, produces through the component a current of 1 ampere
Ohm’s law
For a metallic conductor at a constant temperature, the current through the conductor is directly proportional to the p.d across it’s end
Resistivity of metal
The increases resistance of metal with temperature leads to an increase in the resistivity.Caused by thr ions vibrationg more and hinder the flow of electrons. Resistivity of a metal is proportional to the temperature
Resistivity of semi-conductor
The resistivity decreases as the temperature increases for a semi-conductor. Caused as more charge carriers become available.Resistivity of a semi-conductors is inversely proportional to the temperature
Power
Power is the rate of energy transferred (work done)
Fuse
Fuse is a deliberatley weak link in a circuit so that if the current exceeds their value it will overheat ,melt and break the circuit
3 reasons for a fuse
1) To prevent fires-by providing a weak link they guarante the wire will melt first at the fuse in a safe area and not cause a fire
2) To prevent damage-again the weeak link should be lower (current wise) than any sensitive parts of the electrical applience.
3) To prevent outer case becoming live- if the outer case becomes live via a lose cable then this will result in a large current flowing [combination with earth wire] and below the fuse
Determine the correct fuse for a electrical device
find the current and round up to the nearest whole value
Kwh
when an electrical device , power rating of 1kw, is operating for a time of 1 hr, the energy transferes is 1Kwh
Kirchhoff’s 2nd law
The sum of the e.m.f’s in a loop equals the sum of the p.d’s in that same loop. This is a consequence of conservation of energy
Terminal p.d
is the potential difference across the terminals of a power supply. If the circuit is open and therefore no current is flowing this will be equal to the e.m.f.
Progressive wave
Travel through material or a vacum.Transfer energy from one position to another eg Mechanical/Longitudinal/Transverse
Mechanical wave
Waves which need a medium through which to travel eg sound/seismic/water
Longitudinal waves
The particles of the madianoscilate parallel to the direction of wave velocity eg sound (cannot travel through a vacum)
Transverse waves
The particles of the medium oscillate perpendiculary to the direction of wave velocity eg electromagnetic waves (no medium is needed; they can travel through a vacum
