Electricity Flashcards
What is the equation to calculate the total number of electrons that have flowed in a current?
N = Q/e
What is the equation for calculating charge?
Q = I x T
Define mean drift velocity
The average velocity that charge carriers (electrons) move down the wire.
What are the components of I = AneV?
I = current A = cross sectional area of conductor n = number of free electrons per m^3 e = 1.6 x 10^-19 V = drift velocity
Define emf
Emf is the energy transferred by the supply, per unit charge from other forms, to electrical
Define potential difference
P.d. Is the energy transferred per coulomb of charge from electrical energy to other forms
What is a volt?
1 volt = 1J/C
What is the equation for calculating voltage, when given energy transferred and charge?
In Joules and coulombs
P.d. (V) = Energy transferred (W for work done) / Charge (C)
Define resistance
Resistance is a measure of the opposition a material exerts against the flow of electrons
What causes resistance?
The metal ions interfere with the motion of the electrons, causing resistance.
What is ohms law?
Current in an oh mic conductor is proportional to the voltage across it.
Provided that temperature and other physical conditions are constant.
What is kirchoff’s first law
Sum of the current in = the sum of the currents out, at any junction
What is kirchoff’s second law
Sum of the EMFs = sum of the PDs, around any closed loop
What is the equation to calculate resistivity
Resistance = (resistivity x length) / area R = pl/a
What is the unit of resistivity?
The ohm meter
What is the equation linking power, energy and time?
Power = energy / time
What is the derived equation linking power, current and resistance?
P = I^2 x R
Define a kilowatt hour
It is the amount of energy transferred by a 1KW device in an hour
1KW = 3.6MJ
What is the definition of a coulomb?
A coulomb is the amount of charge that passes a point in a circuit when a current of 1 amp flows for 1 second.
What is an ohm?
1 ohm is the resistance when the ratio of p.d. across a component to current through it is 1 volt per amp
What is power?
Power is the rare at which energy is transferred (or work is done)
1 watt is 1 joule per second
What is the equation that calculates EMF using current and 2 different resistances?
EMF = i(R + r)
EMF = current x (Resistance of circuit + internal resistance of supply)
What is the equation relating voltage, work done and charge?
Voltage = work done (J) / Q (C)
What is the equation that relates energy, power and time?
Energy (J) = power (W) x time (s)
