Electricity Flashcards
Electric current
The flow of charge per unit time, or the rate of flow of charge.
Potential Difference
The energy transferred per unit charge between two points in a circuit.
Resistance
The measure of how difficult it is for charge carriers to pass through a component.
Ohm’s law
For an ohmic conductor, current is directly proportional to the potential difference across it. Given the physical conditions across it remain constant.
Ohmic conductor
Component that follows Ohm’s law.
Semiconductor Diode
The forward bias of a diode is the direction in which it will allow current to flow easily past the threshold voltage, which is the smallest voltage needed to allow current to flow
Filament lamp
Contains a length of metal wire which heats up as current increases, therefore the resistance of this component increases as the current increases.
Resistivity
A measure of how easily a metal conducts electricity. product of resistance and cross-sectional area, divided by the length of the material.
What happens when temperature increases in a metal conductor?
The resistance will increase.
How do thermistors work?
- As the temperature of the thermistor increases, the resistance decreases.
- Increasing the temperature of the atom causes electrons to be emitted from atoms.
- Therefore, the number of charge carriers increases which increases the current which hence lowers the resistance.
What is an application of a thermistor?
Trigger an event to occur when the temperature drops or reaches a certain value. e.g. heating in a room.
Superconductor
A material which, below a certain temperature (known as the critical temperature) has zero resistivity.
What are some applications of superconductors?
Power cables - reduce energy loss through heating to zero.
Strong magnetic fields - Maglev trains and medical applications.
Resistors in series
RT = R1 + R2 + R3 ….
Resistors in parallel
1/RT = 1/R1 + 1/R2 ….
Power
The energy transferred over time.
Current and PD in a series circuit
The current is the same everywhere in the circuit.
PD across all elements is equal to the supply PD (adds up to total).
Current and PD in a parallel circuit
The sum of current across all components adds up to the total. (Adds up)
The PD is the same across each branch.
What is conserved in DC circuits?
Charge and energy are always conserved.
Kirchhoff’s first law
The total current flowing into a junction is equal to the current flowing out of that junction.
Kirchhoff’s second law
The sum of all voltages in a series circuit is equal to the battery voltage.
Potential divider
Several resistors in series connected across a voltage source, used to produce a required fraction of the source potential difference which remains constant.
Variable resistor
Supplies a variable potential difference which will vary the resistance across it.
Light dependent resistor (LDR)
A light dependent resistor’s resistance decreases as light intensity increases.
Internal resistance
caused by electrons colliding with atoms inside the battery, therefore some energy is lost before electrons even leave the battery.
Electromotive force (EMF)
The energy transferred by a cell per coulomb of charge that passes through it.
Terminal PD
The p.d across the resistor R.
Lost volts
p.d across the resistor r this value is equal to the energy wasted by the cell per coulomb of charge.
