Electricity Flashcards
Define electric current
The rate of flow of charge
Define a Coulomb
One Coulomb is the electric charge flowing past a point in a time of one second when there is a current of one Ampere.
What is the formula to calculate the number of electrons?
n = Q/e
What way do electrons flow in a circuit and what way is conventional current?
Electrons flow from the negative to positive terminal of the supply.
Conventional current is from the positive to negative terminal of the supply.
State Kirchoff’s First Law and what is being conserved.
The sum of the currents entering any point in a circuit is equal to the sum of currents leaving the same point. (Conservation of charge)
Define drift velocity
Average displacement of electrons along the wire per unit time, towards the positive terminal of the power supply.
Define number density
The number of conduction electrons per unit volume, that is in 1m^3 of the metal.
What is the equation for number density?
n = N/V
number density = number of conduction electrons / volume of the material
Define potential difference
The energy transferred per unit charge when electrical energy is converted into another form of energy.
Define electromotive force
Energy transferred per unit charge when one other type of energy is converted into electrical energy.
Define a Volt
One Volt is the potential difference across a component when one Joule of energy is transferred per unit charge of one Coulomb.
Define power
The rate of energy transfer
Define kilowatt-hour
The energy transferred by a device with a power of 1kW operating for a time of 1 hour.
What is the equation for Kilowatt-hour?
Energy transferred (kWh) = power of device (kW) x time it runs for (hours)
State Kirchoff’s Second Law and what is conserved
In any circuit, the sum of the electromotive forces is equal to the sum of the potential differences around a closed loop. (Conservation of energy)
What are the circuit rules for series and parallel circuits?
Series: I is constant, V = V1 + V2,
R = R1 + R2
Parallel: I = I1 + I2, V is constant,
1/R = 1/R1 + 1/R2
State Ohm’s Law
Voltage is directly proportional to current for a metal at constant temperature.
Explain how internal resistance affects a circuit
Internal resistance reduces the potential difference available from the power source as charges pass through the source of emf.
What factors affect resistance?
Material of the wire
Length of the wire
Cross sectional area of the wire
Temperature of the wire
Define resistivity
The resistivity of a material at a given temperature is the product of the resistance of a component made of the material and its cross sectional area, divided by its length.
Define electrolyte
A liquid that carries electric charge via ions.
Rank insulators, semi-conductors and conductors from having the highest to lowest number density
Conductors, semi-conductors, insulators.
What does a higher number density mean?
It is a better conductor
What is the equation for terminal potential difference?
Terminal potential difference = emf - lost volts
