Current, Potential Difference and Resistance (2a)

Electric Current

Rate of flow of electric charge

• size of an electric current is amount of current passing through a component each second

Current Unit

measured in amperes or amps

• 1A = 1C/s

Current Flows:

• when a circuit is formed (wire connects two oppositely charged terminals of a cell)

• from positive to negative terminal of a cell

Measuring Current

• measured with ammeter

• ammeter must be connected in series with component to measure

Wire made of metal because:

metal is a good conductor of electricity

Current

flow of negatively charged electrons

Current Equation

Q = I x t

• Q : charge in coulombs (C)

• I: current in amps (A)

• t: time in secs (s)

Voltage

energy transferred per unit charge passing between two points

Voltage Unit

measured in volts

• 1V = 1J/C

Electrons’ energy loss and gain

• flowing through a cell: gaining energy

• flowing through a cell: losing energy

Measuring Voltage

• measured with a voltmeter

• voltmeters must be set up in parallel with component to measure

Voltage Equation

E = Q x V

• E: energy in joules (J)

• Q: charge in coulombs (C)

• V: voltage in volts (V)

Resistance

opposition of a component through the flow of electric current through it

Resistance Unit

• measured in ohms (Ω)

• 1Ω = 1V/ 1A

Current and Resistance (for same Voltage)

• high resistance = lower current

• low resistance = higher current

Wires made of Copper because:

low resistance, so good conductor

Voltage Equation

V = I x R

• V: voltage in volts (V)

• I: current in amps (A)

• R: resistance in ohms (Ω)