parallel resistors

tropicalhotdog · 25th March 2009

I'm tired of my own igonrance about how my gear works, so I've been reading a book on introductory electronics (Gibilisco's Teach Yourself Electricity and Electronics, 4th ed.).

Can someone explain why adding a second (or 3rd or 4th) resistor in a parallel configuration reduces net resistance in a given circuit? That's very counterintuitive, and I haven't seen an explanation of why it works that way.

JohnRoberts · 25th March 2009

Quote:

Originally Posted by tropicalhotdog

I'm tired of my own igonrance about how my gear works, so I've been reading a book on introductory electronics (Gibilisco's Teach Yourself Electricity and Electronics, 4th ed.).

Can someone explain why adding a second (or 3rd or 4th) resistor in a parallel configuration reduces net resistance in a given circuit? That's very counterintuitive, and I haven't seen an explanation of why it works that way.

Think of a resistor like a garden hose.. and resistance is resistance to water flow for a given pressure(voltage). Putting another hose in parallel with the first, for identical water pressure will allow 2x the flow or current.

JR

Minion · 25th March 2009

Quote:

Originally Posted by tropicalhotdog

I'm tired of my own igonrance about how my gear works, so I've been reading a book on introductory electronics (Gibilisco's Teach Yourself Electricity and Electronics, 4th ed.).

Can someone explain why adding a second (or 3rd or 4th) resistor in a parallel configuration reduces net resistance in a given circuit? That's very counterintuitive, and I haven't seen an explanation of why it works that way.

It is hard 2 explain , um , lets say there is a resistor in a curcuit and this resistor is say 8 ohms , it lets a certain ammount of current through based on the source voltage and the resistance , if you put a second resistor in paralell with it that is also 8 ohms it will also let the same ammount of current through and both currents combine which means you are letting twice the ammount of current through two paralell 8ohm resistors than you are with a single 8 ohm resistor and based on ohms law this means the resistance is now 4 ohms as you are getting twice the current as you are with 8 ohms....

I"m not good at explaining this stuff but I hope it helped some...

Cheers

tropicalhotdog · 25th March 2009

I thought of the wire as the garden hose, and the added resistor as a sort of clamp to restrict flow. So is my confusion from not taking into account that adding another resistor actually adds not another clamp, but another line of clamped hose?

Minion · 25th March 2009

Quote:

Originally Posted by tropicalhotdog

I thought of the wire as the garden hose, and the added resistor as a sort of clamp to restrict flow. So is my confusion from not taking into account that adding another resistor actually adds not another clamp, but another line of clamped hose?

By paralelling a resistor you are letting more voltage/current through , think of it as 2 hoses now , both letting current and voltage through...

tropicalhotdog · 25th March 2009

Actually, you are quite good at explaining it. I get it now - thanks.

David Kulka · 25th March 2009

Maybe some of the confusion is due to terminology. If resistors resist the flow of current, how can adding more of them increase the flow of current?

It might seem counter-intuitive, but actually, a resistor and a piece of wire (a "conductor") are not much different. No wire is a perfect conductor; every piece of wire has some amount of resistance. No resistor has infinite resistance, so every resistor has some conductance.

A one ohm resistor and a long piece of hookup wire are nearly same thing, electrically. Actually, you can think of a resistor as a very thin piece of wire.

So, keeping this in mind, you can see that a resistor, even if it is not a very good conductor of electricity, will still conduct some electricity. Connecting a given resistor of them to a circuit with voltage will allow some amount of current to flow. Connecting two identical resistors, in parallel, allow twice as much current to flow.

I hope this makes things clearer, not more confusing!

Mylithra · 25th March 2009

Think of it this way, when you have 1 resistor, you have only 1 path for electricity to take. By adding another resistor in parallel, you add an additional path for electricity to take. Using the water hose analogy, adding a 2nd resistor in parallel will add another hose. Adding resistors in series is like adding an additional clamped hose to the end of the existing clamped hose.

Just wait till you get to the part about Series and Parallel Capacitors. Its the opposite of resistors.

25th March 2009	#1
tropicalhotdog Lives for gear Joined: Mar 2008 Location: NYC Posts: 531 Thread Starter	parallel resistors I'm tired of my own igonrance about how my gear works, so I've been reading a book on introductory electronics (Gibilisco's Teach Yourself Electricity and Electronics, 4th ed.). Can someone explain why adding a second (or 3rd or 4th) resistor in a parallel configuration reduces net resistance in a given circuit? That's very counterintuitive, and I haven't seen an explanation of why it works that way.

25th March 2009	#7
David Kulka Lives for gear Joined: Oct 2004 Location: Burbank, CA, USA Posts: 1,037	Maybe some of the confusion is due to terminology. If resistors resist the flow of current, how can adding more of them increase the flow of current? It might seem counter-intuitive, but actually, a resistor and a piece of wire (a "conductor") are not much different. No wire is a perfect conductor; every piece of wire has some amount of resistance. No resistor has infinite resistance, so every resistor has some conductance. A one ohm resistor and a long piece of hookup wire are nearly same thing, electrically. Actually, you can think of a resistor as a very thin piece of wire. So, keeping this in mind, you can see that a resistor, even if it is not a very good conductor of electricity, will still conduct some electricity. Connecting a given resistor of them to a circuit with voltage will allow some amount of current to flow. Connecting two identical resistors, in parallel, allow twice as much current to flow. I hope this makes things clearer, not more confusing! __________________ http://studioelectronics.biz Service & Restoration of UREI dbx Eventide Marshall AMS Tube Gear and more

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25th March 2009	#8
Mylithra Gear addict Joined: Mar 2008 Posts: 359	Think of it this way, when you have 1 resistor, you have only 1 path for electricity to take. By adding another resistor in parallel, you add an additional path for electricity to take. Using the water hose analogy, adding a 2nd resistor in parallel will add another hose. Adding resistors in series is like adding an additional clamped hose to the end of the existing clamped hose. Just wait till you get to the part about Series and Parallel Capacitors. Its the opposite of resistors.