Confusion about how electricity works

Hi,

There's something about electricity that I don't really understand. Imagine we have a wire whose diameter gradually decreases as you go along (i.e. it gets thinner). The smaller the cross-sectional area, the higher the resistance, but the current remains the same.

What I'm struggling to understand is how the current could possibly remain the same throughout the circuit. Intuitively, there are more electrons in the thicker sections of the wire, and fewer electrons in the thinner sections of the wire. If current is the rate of flow of electrons, how can it be the same in the thinner sections if there aren't as many electrons that can occupy the spaces between the metal ions? Do the electrons move faster in the thinner sections? If so, why does that mean that resistance increases...?

Sorry, I'm just really confused...!

Thanks!

Reply 1

TheFarmerLad

22

Original post by MrLatinNerd

Hi,

There's something about electricity that I don't really understand. Imagine we have a wire whose diameter gradually decreases as you go along (i.e. it gets thinner). The smaller the cross-sectional area, the higher the resistance, but the current remains the same.

What I'm struggling to understand is how the current could possibly remain the same throughout the circuit. Intuitively, there are more electrons in the thicker sections of the wire, and fewer electrons in the thinner sections of the wire. If current is the rate of flow of electrons, how can it be the same in the thinner sections if there aren't as many electrons that can occupy the spaces between the metal ions? Do the electrons move faster in the thinner sections? If so, why does that mean that resistance increases...?

Sorry, I'm just really confused...!

Thanks!

The current doesn't remain the same, the potential difference does. If the resistance increases, the current descreases (assuming p.d. is constant); remember V=IR?

Reply 2

MrLatinNerd

OP

7

Original post by MathsAstronomy12

The current doesn't remain the same, the potential difference does. If the resistance increases, the current descreases (assuming p.d. is constant); remember V=IR?

But isn't current the same at any point in a series circuit?

Reply 3

TheFarmerLad

22

Original post by MrLatinNerd

But isn't current the same at any point in a series circuit?

Yes

(edited 8 years ago)

Reply 4

Kozmo

10

Original post by MrLatinNerd

But isn't current the same at any point in a series circuit?

When we consider a circuit, we consider them with a constant diameter wire (it's almost a given unless stated otherwise). - As a result, there's no point to really get caught up on this idea.

Anyhow:
Connecting a circuit with a multitude of wires would result, I believe, in a change of potential difference (energy transferred per unit of charge that travels through a component - something with resistance = in this case the wire). As a result, the current stays constant, but the potential difference (work done to push that current through a lesser or greater resistance) changes as resistance does.

Think of it is a current passing into a component with a great resistance from a wire with assumed negligible resistance:

the current stays constant if in series, but the potential difference changes and splits accordingly to push x current through the varying resistances.

- This is just what I can think of it to be following all the laws I know. I'll check with my physics teacher :smile:

Reply 5

MrLatinNerd

OP

7

Thanks for all your replies - I think I understand it a bit better now... I find it very difficult to think about electricity intuitively, but maybe that's because electricity isn't that intuitive at all!

Confusion about how electricity works

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