P2a Topic 2 - Controlling and Using Electric Current Flashcards
Voltage is
The driving force that pushes the current round. Kind of like “electrical pressure”.
Unit: volt, V.
Resistance is
Anything in the circuit which slows the flow down.
Unit: ohm
If you increase the voltage
Then more current can flow!
Potential different is
The energy transferred per Unit Charge Passed
1 Volt =
1 joule/coulomb
Current is ___________ at a junction
Conserved!
An ammeter
Measures the current (in amps) flowing through the component
An ammeter must be
Placed in series!
A voltmeter
Measures the voltage or potential difference (in volts) across the component
A voltmeter must be
Placed in parallel!
Fixed resistors: what is the graph like
The current through a resistor (at constant temperature) is proportional to voltage. Different resistors have different resistance, hence different gradients of lines on the graph.
Filament lamp: what is the graph like
As the temperature of the filament increases, the resistance increases, hence the graph is a curve.
Diode: what is the graph like
Current will only flow through the diode in one direction
Potential difference=
Current TIMES BY Resistance
A light- dependant resistor or LDR is a special type of resistor that
Changes its resistance based on how much light there is
LDR: what happens in bright light
The resistance falls
LDR: what happens in darkness
The resistance is highest
A thermistor is like an LDR - but it’s resistance depends on
Temperature
What happens to resistors when electric current passes through them
1) When there is an electric current in the resistor there is an energy transfer which heats the resistor.
2) This energy transfer is due to the electrons colliding with the ions in the lattice that make up the resistor as they move through it.
3) These collisions give the ions in the lattice extra energy, which is emitted as heat. This heating effect increases the resistor’s resistance - so less current will flow, or a greater voltage will be needed to produce the same current.
Electrical power=
Potential difference TIMES BY current
Energy transferred=
Current TIMES BY potential difference TIMES BY time
Current is
Rate of flow of charge round a circuit. Current will only flow through a component if there is a voltage across that component.
Unit: ampere, A.
