Regents PhysicsRegents Physics

Parallel CircuitsParallel Circuits–Ohm’s Law in Parallel CircuitsOhm’s Law in Parallel Circuits

Parallel CircuitsParallel CircuitsSummary1. The potential drops of each branch equals the potential rise of the source.

2. The total current is equal to the sum of the currents in the branches

3. The inverse of the total resistance of the circuit (also called effective resistance) is equal to the sum of the inverses of the individual resistances.

Parallel Circuit and Ohm’s LawParallel Circuit and Ohm’s Law

Voltage in a Parallel CircuitVoltage in a Parallel Circuit

– What is the voltage drop across the resistor What is the voltage drop across the resistor and light bulb?and light bulb?

– Draw a voltmeter that would measure the Draw a voltmeter that would measure the potential difference across the resistor onlypotential difference across the resistor only

12 V cellV Answer: 12 VOLTS

Current in a Parallel CircuitCurrent in a Parallel Circuit

Current in divided in the branchesCurrent in divided in the branches

Resistance of individual resistors determines how much Resistance of individual resistors determines how much current will flow through itcurrent will flow through it

12 V cell e-e-e-e-e-e-

Question: What has higher resistance the resistor or the light bulb?

Draw an ammeter measuring• the current through the light bulb• the total current in the circuit

Equivalent Resistance

A short-cut method to using the equationA short-cut method to using the equation– Find the average of the resistorsFind the average of the resistors– Divide by number of resistorsDivide by number of resistors

is the same as…

is the same as…

Equivalent Resistance con’t

More than 2 resistorsMore than 2 resistors

is the same as…

is approximately…

5+7+12= 24

24/3 = average = 8

8/3 resistors = between 2 - 3

Example of a Parallel CircuitExample of a Parallel Circuit

1) Find current flowing through each resistor

2) Find the total current flowing in the circuit

3) Find the equivalent resistance of the circuit12V

R1 = 2

R2 = 3

R3 = 6