Current, Voltage, and Resistance in a circuit

Characteristics of a circuit

– V is voltage (volts – V)– I is current (amperes or amps – A)– R is resistance ( ohms - Ω)

Voltage

• Also called Potential (don’t confuse this with potential energy)

• Voltage is the Energy per Coulomb provided to the circuit.

• Potential differences are what drive current in a circuit

Voltage

• Measured in volts

How batteries create a voltage difference

Current

• Current is the rate at which charges flow through a circuit

• 1 coulomb in 1 sec = 1 Ampere (Amp)

Direction of the Current flow

• CONVENTIONAL CURRENT– Direction positive charges would move• Away from higher potential (+ on the battery)

• ELECTRON CURRENT– Direction electrons would move• Away from lower potential (- on the battery)

Resistance

• The electrons encounter obstacles as they move through a circuit (this is what creates resistance to the current)

• Measured in ohms

Resistance

• Resistance depends on three properties– Material (resistivity )– Cross-sectional area– length

In Summary

Voltage in a circuit

• When voltage sources are connected in series and in the same direction, their voltages add together.

• If they’re in opposite directions you subtract their voltages (it’s like they’re working against each other)

Resistance in a circuit

• In a series circuit, you add each of the individual resistances

• In a parallel circuit, it’s a little more complex.

Current in a circuit

• The amount of current flowing through a given part of a circuit is determined from the resistance and the voltage using ohm’s law

Chanting Ohmmmmm on the AP exam has not been proven to be

effective.

Ohm’s Law

• V = IR– V is voltage (volts – V)– I is current (amperes or amps – A)– R is resistance ( ohms - Ω)

Determining Voltage, Resistance, and Current in a circuit

That’s great if you have a purely series or parallel circuit but what if there’s a combination of the two,

some kind of, I don’t know, “combination circuit”?

SOLVING THE COMBINATION CIRCUIT

• The basic strategy is to simplify the circuit into a series circuit.

Power

• The power dissipated in a circuit element equals:

P=IV• The total power dissipated by the elements in

a circuit must equal the power supplied by the battery– Basically you have to use all the power and you

can’t use more power than you’re given