P2 Topic 2 - Controlling And Using Electric Current Flashcards
Define resistance.
Resistance is anything in a circuit that reduces the current.
Unit: ohms, Ω
Define current.
The rate of flow of charge around a circuit.
A current will only flow through a component if a voltage is applied.
It is conserved in the circuit, so at a junction, the current entering is equal to the current leaving the junction.
Unit: ampere, A
Define voltage.
Voltage, or potential difference, is the driving force that pushes the current round. It is a bit like the electrical pressure in a circuit.
Unit: volts, V
Describe the voltage-current graph of a fixed resistor.
Directly proportional, always goes through zero, straight line.
Describe the voltage-current graph of a filament lamp.
Goes through zero, as current increases voltage increases up to a point, eventually plateaus
As the temperature of the lamp increases, the resistance also increases, hence the curve in the graph
Describe the voltage-current graph of a diode.
Exponential graph starting at zero, all negative values for voltage have zero current as diodes only let the current flow one way
How does light affect the resistance in an LDR?
Brighter light - resistance falls
Darker - resistance increases
How does temperature affect a thermistor?
Hot - resistance drops
Cold - resistance increases
Why do resistors heat up when a current is passed through them?
As electrons pass through the resistor, they collide with ions that make up a lattice in the component. These collisions give the ions more energy which they give off as heat, which increases the resistance.
What is the equation for power?
Power = Voltage x Current P = V x I
What is the equation for energy transferred?
Energy Transferred = Current x Voltage x Time
E = I x V x t
