P2 ELECTRICITY
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what can be said about the value of current at any point in a single closed loop?
current is the same at all points in a closed loops
2 factors that current in a circuit depend on?
potential difference resistance
define electrical current
the rate of flow of electrical charge
define an ohmic conductor?
a conductor where resistance remains constant as the current changes.
name four non-ohmic conductors?
lamps , diodes , thermistor , LDRs
name two ohmic conductors?
wires , fixed , resistors
describe how the resistance of a filament lamp changes with temperature?
as temperature increases , the resistance increases. ions in metals have more energy , so vibrate more often causing more collisons with electrons as they flow through the metal , creating greater resistance to current flow
describe how a diode conducts electricity
it only conducts electricity in one direction as it has a very high pressure in the backwards direction
describe how the resistance of a thermistor changes with temperature ?
as temperature increases , the resistance decreases.
describe a use of thermistors
thermistors can be used in thermostat circuits to automatically turn the heating on when it gets too cold , or switch it off when its gets hot
describe how the resistance of an LDR changes with light intensity
as light intensity increases , the resistances decreases.
describe a use of LDRs
can be used in automatic lights , to turn on automatically when it gets dark ,and switch off automatically when it gets light
which two things are needed for charge to flow through a circuit
the circuit must be closed and there must be a source of potential difference
state the rule for current in a series circuit?
the current will be the same at all points in a series circuit.
if the resistance of a component increases , what will happen to the current through that component?
it will decrease
unit for potential difference
Volts (V)
units for resistance
Ohms (Ω)
describe how current is measured
with an ammeter connected in series
describe how voltage is measured
with a voltmeter connected in parallel to the component you want to measure
what are the two ways that a component can be connected in a circuit ?
series (same loop) parallel (adjacent loop)
give the rule for current in series current
the current is the same at all points in a series current
give the rule for current in parallel current
the current in a parallel circuit is shared between the branches of the circuit .
give the rule for resistance in a parallel circuit
when resistors are connected in parallel , the total resistance is less than the resistance of the smallest resistor.
give the rule for resistance in a series circuit
the total resistance in a series circuit is the sum of all the individuals resistances