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# Can someone explain voltage and current in both series and parallel circuits?

1. So far, I know that in a series circuit the current is the same across each component, so bulbs get dimmer in a series circuit because each bulb has less current.

I have also learnt that in a parallel circuit, current is shared between each component running in parallel. What does that mean? Also, when you add more bulbs into a parallel circuit, why dont they get dimmer like they would in a series circuit?

On top of this, can someone also explain how voltage changes in a parallel and series circuit.

Thanks
2. Two things to be clear about when talking circuits;

Current is the rate of flow of charge; it helps to think of it physically as some sort of flow.
Voltage/potential difference is the work done per unit charge across a component; it helps to think of this as a driving force.

So when you say 'each bulb gets dimmer in a series circuit because each bulb gets less current', that's not entirely true - if we're thinking of current as flow, each bulb will have the same current pass through it. What really makes the bulbs dimmer when we add more is that each bulb will have a smaller share of the battery voltage = less driving force across each bulb.

In parallel circuits, when the wire branches, each branch will have the same voltage.. Even though the current has to split and each branch receives less current than in the series circuit, there's still the same driving force across each branch, so there's no dimming.
3. (Original post by aerofanatic)
Two things to be clear about when talking circuits;

Current is the rate of flow of charge; it helps to think of it physically as some sort of flow.
Voltage/potential difference is the work done per unit charge across a component; it helps to think of this as a driving force.

So when you say 'each bulb gets dimmer in a series circuit because each bulb gets less current', that's not entirely true - if we're thinking of current as flow, each bulb will have the same current pass through it. What really makes the bulbs dimmer when we add more is that each bulb will have a smaller share of the battery voltage = less driving force across each bulb.

In parallel circuits, when the wire branches, each branch will have the same voltage.. Even though the current has to split and each branch receives less current than in the series circuit, there's still the same driving force across each branch, so there's no dimming.
So in a parallel circuit, each branch has the same voltage (but the "electricity" can only flow down one branch at a time)?

And in a series circuit, the voltage is split between the components? (eg a 9V battery could supply three components with voltage, such as ones with 3V, 4V and 2V? Am I correct about these two?

And how is current split/issued out in both a parallel and series circuit?
4. (Original post by blobbybill)
So far, I know that in a series circuit the current is the same across each component, so bulbs get dimmer in a series circuit because each bulb has less current.

I have also learnt that in a parallel circuit, current is shared between each component running in parallel. What does that mean? Also, when you add more bulbs into a parallel circuit, why dont they get dimmer like they would in a series circuit?

On top of this, can someone also explain how voltage changes in a parallel and series circuit.

Thanks

Okay here are the rules:

Series circuit:

The current is the same at all points. This means that the current across each electrical component in a circuit is the same for every single component in the circuit. If a circuit has a supply current of 3A then each component in the circuit will have a current of 3A running through it.

For voltage in a series circuit the sum of the voltage across each component adds up to the supply voltage. It's also useful to note that the bigger the share of the resistance a component has the more voltage it has. If a circuit has a supply voltage of 10V and 2 lamps are connected, the sum of these 2 lamps will add up to 10V.

Parallel Circuit:

For current in a parallel circuit the sum of the currents across each branch adds up to the supply current. If a circuit has a supply current of 5A and has two branches connected, then the current in these two branches must add up to 5A.

For voltage in a parallel circuit the voltage across each branch equals the supply voltage. If a circuit has a supply voltage of 10V and 3 branches are connected, it doesn't matter how many branches are connected the voltage across each 3 branches will equal 10V.

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5. (Original post by blobbybill)
So in a parallel circuit, each branch has the same voltage (but the "electricity" can only flow down one branch at a time)?

And in a series circuit, the voltage is split between the components? (eg a 9V battery could supply three components with voltage, such as ones with 3V, 4V and 2V? Am I correct about these two?

And how is current split/issued out in both a parallel and series circuit?
In a parallel circuit each branch has the same voltage across it. Quick note to clarify a detail: voltage can only be ACROSS components, whereas current flows THROUGH them.

Actually electricity, or specifically what you probably mean as current will flow through both branches; how much each branch receives just depends on the components you have. The only exception is if you introduce a short-circuit but at GCSE level you don't have to worry about that.

Yep, voltage can possibly be split in those proportions; that depends on the resistance of each component (V=IR).

In a series circuit, it's nice and easy to calculate how the voltage is split.
You first realise that the sum of voltages across components equals what the source/cell/battery provides. Then you find the current that has to go through every component, since everything's in parallel. Then simply use V=IR to get the voltages and make sure they add up to the source.

In a parallel circuit, the two tricks are realising current splits at a branch and the voltage across each branch is the same. Everything will make more sense through doing some examples.
6. (Original post by RossB1702)
For voltage in a parallel circuit the voltage across each branch equals the supply voltage. If a circuit has a supply voltage of 10V and 3 branches are connected, it doesn't matter how many branches are connected the voltage across each 3 branches will equal 10V.

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This is assuming there isn't a component between the source and the branches.
7. (Original post by aerofanatic)
This is assuming there isn't a component between the source and the branches.
Are you sure ? The voltage across each branch will always equal the supply voltage so why would a component that is not in the branch affect it ? You mind explaining it to me if this is the case ? Thanks.

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8. (Original post by RossB1702)
Are you sure ? The voltage across each branch will always equal the supply voltage so why would a component that is not in the branch affect it ? You mind explaining it to me if this is the case ? Thanks.

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Check out example 1 from this link:
http://www.physicsclassroom.com/clas...ation-Circuits

Resistors R1 and R4 being where they are means the parallel branches don't have the source voltage across them. The parallel resistors have a series equivalent (1/Rt=1/R2 + 1/R3) so you effectively have the parallel branches as being equivalent to a single resistor in series.

9. (Original post by aerofanatic)
Check out example 1 from this link:
http://www.physicsclassroom.com/clas...ation-Circuits

Resistors R1 and R4 being where they are means the parallel branches don't have the source voltage across them. The parallel resistors have a series equivalent (1/Rt=1/R2 + 1/R3) so you effectively have the parallel branches as being equivalent to a single resistor in series.

I'll give it a read. I do Scottish Advanced Higher Physics btw. What level you studying or have studied ?

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10. (Original post by RossB1702)
I'll give it a read. I do Scottish Advanced Higher Physics btw. What level you studying or have studied ?

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Ah right, good stuff buddy. You ought to give that a read then. I'm studying Aeronautics at uni.
11. (Original post by aerofanatic)
Ah right, good stuff buddy. You ought to give that a read then. I'm studying Aeronautics at uni.
Nice, my brother is actually applying for aero-mechanical engineering at uni. I myself are applying for naval architecture/marine engineering and also mechanical engineering. How's your course going, you enjoying it ?

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12. (Original post by RossB1702)
Nice, my brother is actually applying for aero-mechanical engineering at uni. I myself are applying for naval architecture/marine engineering and also mechanical engineering. How's your course going, you enjoying it ?

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Nice to hear of the interest in Engineering! Go for it, you get to see how all this maths and physics is useful. My course is good but pretty tough.. Loads to do always but I do enjoy it.
13. (Original post by aerofanatic)
Nice to hear of the interest in Engineering! Go for it, you get to see how all this maths and physics is useful. My course is good but pretty tough.. Loads to do always but I do enjoy it.
That's good to hear. Keep working hard and good luck.

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