Electricity Flashcards
Define electric current and give a symbol and unit
Electric current as the rate of flow of charge, measured in A (I)
Define potential difference and give a symbol and unit
Potential difference as work done per unit charge (V)
How do insulators work
electron attached to atom and cant move away
How do metallic conductors work
some electrons unattched so carry charge to positive terminal
Semiconductor
number of charge carriers increases with temperature therefore resistance decreases as temperature increases
Ohms law states that
I is directly proportional to the pd (V)
EMF =
electrical energy produced per unit charge passing through a point
When plotting current (x) against pd (y) for an ohmic conductor the gradient =
1/R
resistivity(p) =
resistance * cross sectional area / length
Superconductor and applications =
Superconductivity as a property of certain materials which have zero resistivity at and below a critical temperature which depends on the material. Applications (e.g. very strong electromagnets, power cables as can transfer electrical energy without wasting energy).
At any junction in a circuit….
the total current leaving the junction = the total current entering the junction
The current passing through two or more components in series is
the same throughout each component
Potential difference =
energy transfer per coulomb of charge
For 2 or more components in series, the total potential difference across all the components is
equal to the sum of the potential difference across each component
In series, V0 =
V1 + V2 + V3
In parallel, V0 =
V1 = V2 = V3
For any complete loop of a circuit, the sum of the emfs round the loop is
equal to the sum of the potential drops around the loop
In series, R0 =
R1 + R2 + R3 same current different pd
In parallel, 1/R =
1/R1 + 1/R2 same pd different current
Rate of heat transfer =
RI^2
E=IVt
P=IV
P=RI^2
Emf =
Electrical energy, E / Charge, Q
IR +Ir = terminal pd + lost pd (pd across internal resistance)
V1 - V2 / I2 - I1
Internal resistance is
the loss of potential difference per unit current
the resistance of the battery itself within the circuit (lost volts)
Circuit with emf, e and two resistors r and R, current =
I = e/R + r
When plotting Current (x) against terminal voltage (y) what can you get
y intercept = emf
gradient = negative internal resistance