Current Electricity Flashcards
Current
Rate of flow of charge
Coulomb
Unit of charge. If one amp flows for one second then one coulomb of charge has passed
Potential difference
Work done per unit charge ( joules/coulomb)
Ammeter
Used to measure current, has zero resistance
Voltmeter
Used to measure Potential difference. Ideally has infinite resistance
Whenever charge flows through a component……
energy is transferred
Ohmic conductor
Provided that temperature is constant, the current flowing through an ohmic conductor is proportional to the applied voltage
Gradient of an I/V graph tells us …..
1/Resistance
I/V for filament lamp
Produces a curved graph as resistance changes as more current flows. The current heats the filament causing resistance to increase
Diode
Allow current to flow in one direction (forward bias)
Require a voltage of around 0.6V before they will conduct
Threshold voltage
Minimum voltage needed for a diode to conduct Most diodes require a voltage of around 0.6V before they will conduct
LDR
Light dependant resistor. The greater the light intensity, the lower the resistance. Light provides the energy needed to release more electrons (charge carriers)
Thermistor
Resistance decreases with increasing temperature. Thermal energy provides electrons with energy needed to become free and thus a charge carrier
Resistivity
A material property not a property of an object. How much a particular material resists the flow of current
Superconductor
Materials that can exhibit zero resistance
Critical temperature
The temperature below which a material becomes superconducting and has zero resistance
Power
Rate of transfer of energy
Watt
Unit of power, equal to one joule transferred per second
Internal resistance
The resistance that all batteries and power sources have
EMF
the amount of energy that the battery transfers to each coulomb of charge
EMF is equal in magnitude to
The voltage across the components in the circuit plus the voltage dropped across the internal resistance of the battery
The voltage across the components in a circuit (the terminal p.d) is equal to
The EMF minus the voltage dropped across the internal resistance
The area under a graph of current against time is equal to
The total charge flow
To find EMF from a graph of voltage against current you find the
Intercept of the line on the voltage axis
Kirchoff’s first law
Total current entering a junction = total current leaving a junction
Kirchoff’s second law
The total EMF around a series circuit = sum of the p.ds across each component in the circuit
Potential divider
At it’s simplest, a circuit with a voltage source and two fixed resistors. The voltage is split between the two resistors so you can tap off different values of voltage
Potentiometer
A potential divider with a variable resistor and a fixed resistor. It allows us to obtain any voltage from 0V to the supply voltage
