Electricity

Current Electricity
 Current in series stays the same
 Current in parallel is different
 Potential difference in parallel is the same
 Potential difference in series is same

Potential Difference
Definition: the work done per unit positive charge.
 Measured in volts V.
 Instrument used is the voltmeter.
Connected in parallel.
Must have complete conducting pathway (connected to both sides of battery.)
Has very high resistance to prevent current passing through it.
 The sum of the Potential Difference across all the resistors in the external circuit is
equal to the potential difference of the battery.
 Work is done when the charge passes through a resistor.
 No work is done by the charge when it passes through the conducting wire.
 Switch open (battery reads EMF if not full pathway to each end of battery.)

EMF
Definition: total energy supplied by the cell per coulomb of charge.
 EMF does not change.
 Voltmeter reads EMF when no current flowing through the external circuit.
 If there is an internal resistor the voltmeter will read the amount of PD dissipated to
the external circuit.
Internal resistor = volts lost.
EMF = I (Rext + r)
r is CONSTANT.
Current is the same as current in external circuit.
 EMF = Vext + Vint or Vint = EMF – V ext.

Current
Definition: rate of flow of charge.
 Unit is amperes A.
 Current is the same at every point in series circuit.
 Current splits in pathways when there are parallel resistors (must equal total
current.)
 Current inversely proportional to resistance.
 Instrument used in ammeter
Connected in series in a circuit.
Has very low resistance (not to affect current flowing though.)




Resistance