Circuit Basics and Ohms Law

Types of Circuits There are two basic types of circuits SeriesParallel

Series In a series circuit there is only one path for the current to flow The voltage drops across each load The current remains constant Ammeters (current meters) are connected in 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

Parallel In a parallel circuit there are multiple paths for the current to flow The voltage is constant The current divides Voltmeters 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 Law Simply stated Ohm’s Law can be stated This can be shown in Ohm’s triangle below I V R

Using the pyramid Cover the variable you want to find Either multiply or divide the remaining variables To find V, cover V – this leaves I & R to be multiplied To find I, cover I – this leaves V divided by R I V R

Breaking Down a Series Circuit Since there is only one path, the total of the resistors is 9 Ω (ohms) Using the triangle, with 12 volts and 9 Ω there must be 1.33 amps in the circuit 12 Volts 3 Ω 4 Ω 2 Ω

Breaking Down a Series Circuit Again, using the triangle with 1.33 amps and 3 Ω, gives us 4 volts For the 1.33 amps and 2 Ω, we get 2.67 volts And finally with the 1.33 amps and 4 Ω, we get 5.33 volts These all add (4v+2.67v+5.33v = 12 v) 12 Volts 3 Ω 4 Ω 2 Ω 1.33 Amps Current

Breaking Down a Parallel Circuit No matter which resistor path we take, the potential difference is still 12 volts. So we can use 12 volts for each resistor and calculate the current for each branch 12 Volts 3 Ω 4 Ω 2 Ω

Breaking Down a Parallel Circuit With 12 volts across the 3 Ω, we can get 4 amps by using the triangle We will get 6 amps with the 2 Ω resistor and 3 amps with the 4 Ω resistor This will total 13 amps (much more than the series circuit) 12 Volts 3 Ω 4 Ω 2 Ω

Breaking Down a Parallel Circuit If the voltage total is 12 volts and the current total is 13 amps, what is the total resistance? Ω As you add branches of resistors in parallel the total resistance drops This is why you get enough current to blow a circuit when you plug too many things into one outlet 12 Volts 3 Ω 4 Ω 2 Ω