Ohm’s Law Parallel Circuits

Parallel Circuit

A parallel circuit is one in which all positive terminals are connected to a common point and all negative terminals are connected to a second common point.As a result, the current flows through separate branches to reach components.

With this type of circuit, it is helpful to remember:

The voltage is the same across each branch.The total current (amperes) is equal to the sum of the individual branch currents.The total circuit resistance is always less than the smallest resistance of any branch. (Power must be removed to measure resistance with an ohmmeter.)

Voltage, Current, and Resistance Relationship in a Parallel Circuit.

Calculating Resistance in a Parallel Circuit

Remember, in calculating the total resistance of a series circuit, add up each resistance. RT=R1+R2+R3

Calculating total resistance is more complicated in parallel circuits.When resistances are combined, the total resistance grows smaller.

The more paths for electricity to flow, the easier it is for the source to “push” current through the circuit.

Consider a water tank with a pipe and two faucets.

If one was opened, the water would flow at about one gallon per minute, emptying in ten minutes.

Consider a water tank with a pipe and two faucets.

If one was opened, the water would flow at about one gallon per minute, emptying in ten minutes.

Consider a water tank with a pipe and two faucets.

If the second faucet is the same as the first (flowing at one gallon per minute), twice as much water will flow.

Consider a water tank with a pipe and two faucets.

This means total flow will now be two gallons per minute.The 10-gallon tank will empty in five minutes.In an electrical circuit, the current flow is twice as much, and the opposition to current is half as much.

Parallel circuit

In an electrical circuit, the same laws of physics apply.As the resistances are combined in parallel and more paths to current flow are made, total resistance decreases and total current flow increases.

Parallel circuit : with only two resistors

In calculating total resistance of two parallel resistors, use the following formula:

Parallel Resistances of Equal Value

This circuit is a parallel circuit with four resistive loads.All the load resistance are of equal value.

Parallel Resistances of Equal Value

To calculate total resistance in a parallel circuit with branch resistances of equal value, use the following:

Parallel Circuit : resistances of equal value

Parallel Circuit :More then two

When more than two loads are connected in parallel, the above formulas CAN NOT be used to calculate RT.

If the loads are 200, 275, 330 all in parallel, calculate total resistance (RT) using the following formula.

The End