Electricity

not completed yet

charge (Q)

• measured in C (coulombs)

• e = 1.6×10^-19

current (A)

• measured in A (amperes)

• rate of flow of charge

• created when a charged particle experiences an electric force

• movement of electric charge

• flows from +ve to -ve → electrons move in opp direction

charge formula

Q = It

• charge = current x time

voltage (V)

• measured in V (volts)

• electric potential difference between two points

• driving force that pushes electric current through a circuit

• amount of energy a component transfers per unit charge passing through it

voltage formula

V = E/Q (joules/coulombs)

• voltage = energy/charge

what is EMF?

• work done / energy transferred by a voltage source / battery / cell per unit charge

• pd across terminals when no current is flowing → potential to push charge

resistance of voltmeters

very high resistance → draws nearly no current

what is the difference between supply voltage and EMF?

• EMF: total energy supplied by the source per unit charge

  • potential difference across the terminals of a power source when no current is flowing (open circuit).

  • represents max p.d the source can provide

  • the work done by the source to move charge around the entire circuit, including through its own internal resistance

• Supply Voltage (Terminal Potential Difference): p.d across the terminals of a power source when current is flowing (closed circuit).

  • always less than the EMF due to the voltage drop across the internal resistance of the source (V = \text{EMF} - Ir → I is current + r is internal resistance)

  • actual voltage available to the external circuit

why does EMF exist?

because the battery is doing work to separate charges, not because the chargers are already moving (current)

• chemical reactions inside the battery are separating charge → creates an electric field bet. the terminals → even though no current is flowing, battery still maintains a potential difference

EMF formula

ε = E/Q

• EMF = energy /charge

what is the difference between voltage and potential difference?

nothing lol

what is potential difference?

work done per unit charge when passing through an electrical component

potential difference formula

V = W/Q

• p.d = work done/charge