CURRENT ELECTRICITY & DC CIRCUIT Flashcards
define current
current is the rate of flow of electric charge through a given cross-section of a conductor
formula for calculating current
I = Q/t
si unit of current = ampere
instrument to measure current
- series/parallel
- resistance?
ammeter
- connected in series
- very low resistance
define conventional current
refers to the flow of positive charge
- opposite direction to electron flow
define e.m.f
electromotive force of a source refers to the work done in driving a unti charge(e.g. 1C) across the whole circuit
formula for calculating emf
E = W/Q
- si unit = volt (V)
emf measured using
voltmeter
- the positive terminal is connected to the positive terminal of battery and negative terminal to negative terminal of batter
define potential difference/ voltage
potential difference of a component refers to the work done in driving a unit charge (e.g. 1C) through the component
formula for p.d.
V = W/Q
p.d. is measured using
- series/parallel
- resistance
voltmeter
- parallel
- very high resistance
define resistance
resistance of a component is the ratio of the potential difference V, applied across it to the current flowing through it I.
si unit of resistance
ohm
rheostat
variable resistor
- used to vary amount of current flowing through a circuit
define Ohm’s Law
ohm’s law states that for a metallic conductor the potential difference applied across it is directly proportional to the current flowing through it provided that physical conditions like temperature remain constant.
formula for resistance( ohmic conductor)
- shape of IV graph for ohmic conductor
R = V/I
- a straight line passing through the origin
- where the gradient represents the resistance
explain resistance of filament bulb
as the current increases, the temperature increases, thus resistance increases, thus voltage increases
formula of resistance in terms of resistivity
resistance = (resistivity x length )/ cross sectional area
si unit of resistivity
ohm metre
why is nichrome used to make heating coils
nichrome has a high resistivity
- thus a high resistance
- thus will generated more thermal energy when current passes through it
current and pd in series and parallel circuit
- same/different
series
- current constant
- V different
- R different
parallel
- V same for every branch
- I different
_ 1/R = 1/R1 + 1/R2 +….
advantages of parallel circuit over series
disadvantage of parallel circuit
advantage
- bulb glow more brightly
- if bulb doesn’t work, others still glow
disadvantage
- higher consumption of power
use of potential divider
provide a fraction of voltage of source to another part of circuit
formula potential divider
V out = (R1/R1+R2) x Ve
define input transducer
input transducers are devices that convert non-electrical energy to electrical energy
light dependent resistor and thermistor
relationship b/w resistance and temeprsture/light intensity
LDR
- light increase - resistance decrease
Thermistor
- temp increase - resistance decrease
why cells with different emfs are not connected together in parallel
- excessive current flow
- very dangerous
