Circuit Basics and Ohms LawCircuit Basics and Ohms Law

Types of CircuitsTypes of Circuits

There are two basic types of circuitsThere are two basic types of circuits

SeriesSeries

ParallelParallel

SeriesSeries

In a series circuit there is only one path for In a series circuit there is only one path for the current to flowthe current to flow

The voltage drops across each loadThe voltage drops across each load

The current remains constantThe current remains constant

Ammeters (current meters) are connected Ammeters (current meters) are connected in seriesin series

Voltage source such as battery or fuel cell

Resistor or load – something that uses the electricity (i.e. light bulb, LCD screens…)

Only one path for the current to follow = SERIES

ParallelParallel

In a parallel circuit there are multiple paths In a parallel circuit there are multiple paths for the current to flowfor the current to flow

The voltage is constantThe voltage is constant

The current dividesThe current divides

Voltmeters are connected in parallelVoltmeters are connected in parallel

Voltage source such as battery or fuel cell

Resistor or load – something that uses the electricity (i.e. light bulb, LCD screens…)

Current must split to pass through each of the three resistors = PARALLEL

Ohm’s LawOhm’s Law

Simply stated Ohm’s Law can be statedSimply stated Ohm’s Law can be stated

This can be shown in Ohm’s triangle belowThis can be shown in Ohm’s triangle below

V IR

I

V

R

Using the pyramidUsing the pyramid

Cover the variable you want to findCover the variable you want to find

Either multiply or divide the remaining Either multiply or divide the remaining variablesvariables

To find V, cover V – this leaves I & R to be To find V, cover V – this leaves I & R to be multipliedmultiplied

To find I, cover I – this leaves V divided by RTo find I, cover I – this leaves V divided by R

I

V

R

Breaking Down a Series CircuitBreaking Down a Series Circuit

Since there is only Since there is only one path, the total of one path, the total of the resistors is 9 the resistors is 9 ΩΩ (ohms)(ohms)

Using the triangle, Using the triangle, with 12 volts and 9 with 12 volts and 9 ΩΩ there must be 1.33 there must be 1.33 amps in the circuitamps in the circuit

12 Volts

3 Ω

4 Ω

2 Ω

Breaking Down a Series CircuitBreaking Down a Series Circuit

Again, using the triangle Again, using the triangle with 1.33 amps and 3 with 1.33 amps and 3 ΩΩ, , gives us 4 voltsgives us 4 volts

For the 1.33 amps and 2 For the 1.33 amps and 2 ΩΩ, we get 2.67 volts, we get 2.67 volts

And finally with the 1.33 And finally with the 1.33 amps and 4 amps and 4 ΩΩ, we get , we get 5.33 volts5.33 volts

These all add These all add (4v+2.67v+5.33v = 12 v)(4v+2.67v+5.33v = 12 v)

12 Volts

3 Ω

4 Ω

2 Ω

1.33 Amps Current

Breaking Down a Parallel CircuitBreaking Down a Parallel Circuit

No matter which No matter which resistor path we take, resistor path we take, the potential the potential difference is still 12 difference is still 12 volts.volts.

So we can use 12 So we can use 12 volts for each resistor volts for each resistor and calculate the and calculate the current for each current for each branchbranch

12 Volts

3 Ω

4 Ω

2 Ω

Breaking Down a Parallel CircuitBreaking Down a Parallel Circuit

With 12 volts across the With 12 volts across the 3 3 ΩΩ, we can get 4 amps , we can get 4 amps by using the triangleby using the triangle

We will get 6 amps with We will get 6 amps with the 2 the 2 ΩΩ resistor and resistor and

3 amps with the 4 3 amps with the 4 ΩΩ resistorresistor

This will total 13 amps This will total 13 amps (much more than the (much more than the series circuit)series circuit)

12 Volts

3 Ω

4 Ω

2 Ω

Breaking Down a Parallel CircuitBreaking Down a Parallel Circuit

If the voltage total is 12 volts If the voltage total is 12 volts and the current total is 13 and the current total is 13 amps, what is the total amps, what is the total resistance?resistance?

0.923 0.923 ΩΩ

As you add branches of As you add branches of resistors in parallel the total resistors in parallel the total resistance dropsresistance drops

This is why you get enough This is why you get enough current to blow a circuit current to blow a circuit when you plug too many when you plug too many things into one outletthings into one outlet

12 Volts

3 Ω

4 Ω

2 Ω