# Elec mcq help pls

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#1
Hi how do i do this question pls? Whats the fastest way of doing it?
Last edited by Htx_x346; 1 month ago
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1 month ago
#2
The current is the pd across the variable resistor / resistance of variable resistor. Then work out total resistance by doing emf / current.

This allows you to work out the internal resistance of the cell which you should label in your diagram.

From then on, it’s okay I would say
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#3
The current is the pd across the variable resistor / resistance of variable resistor. Then work out total resistance by doing emf / current.

This allows you to work out the internal resistance of the cell which you should label in your diagram.

From then on, it’s okay I would say
Okay so r is 4
Do i need to work out the new current? Then do V=i/r again?

literally why is this question like 5 parts long lol
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1 month ago
#4
(Original post by Htx_x346)
Okay so r is 4
Do i need to work out the new current? Then do V=i/r again?

literally why is this question like 5 parts long lol
You could, or just use the potential divider formula, whichever you find easier
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#5
You could, or just use the potential divider formula, whichever you find easier
Ok idk what im doing wrong

v=2(4/12) gives 0.67
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1 month ago
#6
(Original post by Htx_x346)
Ok idk what im doing wrong

v=2(4/12) gives 0.67
The resistance of the whole circuit is 16, you want the pd across the terminals (I.e circuit so emf - lost volts), so you use the load resistance, meaning you’d use 12/16 instead
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#7
The resistance of the whole circuit is 16, you want the pd across the terminals (I.e circuit so emf - lost volts), so you use the load resistance, meaning you’d use 12/16 instead
Ohhhh wait
They want the voltage across the terminals of the cells. So 4/16?
sorry i dont get why you did 12/16
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1 month ago
#8
(Original post by Htx_x346)
Ohhhh wait
They want the voltage across the terminals of the cells. So 4/16?
sorry i dont get why you did 12/16
Terminals of the cell means the pd across the whole circuit, this doesn’t include the lost volts. If you did 4/16, you’d be finding the lost volts.

Terminal pd means the pd across the circuit that isn’t lost (emf - lost volts)
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1 month ago
#9
(Original post by Htx_x346)
Okay so r is 4
Do i need to work out the new current? Then do V=i/r again?

literally why is this question like 5 parts long lol
Just going to point out that you could skip the entire first step just by spotting that the voltage is split in a 1:1 ratio. Though calculating it by finding the current works just as well.

The resistance of the whole circuit is 16, you want the pd across the terminals (I.e circuit so emf - lost volts), so you use the load resistance, meaning you’d use 12/16 instead
If it makes it any easier to think about you could use 4/16 and just find the lost volts directly and then subtract that from 2V to find the potential difference in the rest of the circuit. What Driving_Mad does just skips the additional step of subtracting the lost volts and finding the Pd in the actual circuit, same thing but using 12/16 is faster and leaves less room for error if you're in a rush
Last edited by Skiwi; 1 month ago
1
1 month ago
#10
Just realized i quoted the wrong post (Original post by Htx_x346)
Ohhhh wait
They want the voltage across the terminals of the cells. So 4/16?
sorry i dont get why you did 12/16
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#11
Terminals of the cell means the pd across the whole circuit, this doesn’t include the lost volts. If you did 4/16, you’d be finding the lost volts.

Terminal pd means the pd across the circuit that isn’t lost (emf - lost volts)
Oh i didnt know that, i always assumed terminals of the cell meant p.d across the cell.
thanks!

(Original post by Skiwi)
Just going to point out that you could skip the entire first step just by spotting that the voltage is split in a 1:1 ratio. Though calculating it by finding the current works just as well.

If it makes it any easier to think about you could use 4/16 and just find the lost volts directly and then subtract that from 2V to find the potential difference in the rest of the circuit. What Driving_Mad does just skips the additional step of subtracting the lost volts and finding the Pd in the actual circuit, same thing but using 12/16 is faster and leaves less room for error if you're in a rush
Thanks that makes sense!
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#12

So this means pd in the circuit basically?
1
1 month ago
#13
(Original post by Htx_x346)

So this means pd in the circuit basically?
PD ACROSS TERMINALS = EMF - LOST VOLTS

emf tends to be given

lost volts = Ir where I is the current, and r is internal resistance
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#14
(Original post by itslitbro)
PD ACROSS TERMINALS = EMF - LOST VOLTS

emf tends to be given

lost volts = Ir where I is the current, and r is internal resistance
😊 thanks
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