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## Class 10 Physics (India)

### Course: Class 10 Physics (India)>Unit 3

Lesson 5: Series and parallel resistors

# Parallel resistors (part 2)

Multiple resistors in parallel can be combined into a single equivalent resistor. Created by Willy McAllister.

## Want to join the conversation?

• So, if resistors are connected by a common point, they're immediately considered in parallel?
• Hello Levi,

Correct, it's like two people holding hands:

Left to left plus right to right is parallel.

Left to right plus right to left is still parallel as resistors generally do not care which direction they are installed.

Regards,

APD
• is there another analogie for parallel resistors
• Hello Ethan,

Do you recall those problems involving pumps? For example if a pump can empty a swimming pool in 1/2 hour and another pump can empty the pool in 1/3 hour, how long does it take both pumps operating together to empty the pool?

Here is another: A car gets 30 miles to the gallon and another car gets 20 miles to the gallon. What is there combined millage if they travel together.

I hope these analogies help. It's all about flow of material...

Regards,

APD
• how do we know that voltage for both the R1 and R2 resistor is the same meaning why is it that if they share the same nodes then they are going to have the same voltage?
• If I will connect 10000 resisters to a circuit consisting of a battery which is a 9v battery. will all these 10000 resisters get the same 9volts?
• If all 10,000 resistors are connected in parallel, yes, each one will have 9v across its terminals.

The ideal parallel connection assumes the wires connecting the resistors are ideal (zero resistance) wires. If you try this experiment in real life you have to use real wires, which have a very small (but not 0) resistance. With that many resistors you might end up with a small extra resistance from the wire. "small" means less than 1 ohm.
• So what you’re basically saying is...
Series circuits- current stays the same and voltage changes ( voltage drops )
Parallel circuits- voltage stays the same, and the current changes ( split current )? Is that correct?
• Yes that is correct @Dionna Huett
(1 vote)
• Each current calculation for each of the resistors is just using Ohm's Law, yeah?
(1 vote)
• That is correct. Once you find the voltage across the parallel connection the individual currents are found with Ohm's Law, i = v/R.
• How come the current, that is entering the node, "knows" how to "split itself" into currents such that Ohm's law gives equal voltages? In other words, how does the current know what kind of resistor is ahead? Would it be something similar to road traffic, when a slow traffic would mean a lot of cars and fast traffic means few cars in terms of density?
• This is a good question. I compare this electrical situation with what happens to the flow of water in a shallow creek. When you drop a rock into the water the current splits and flows around either side of the rock. The water molecules don't "know" or "decide" how to split. There is no choosing which side to go on, it just happens.

It's best not to think about the speed of current or electrons. This splitting happens no matter how fast the electrons or water is moving.