GCSE Physics Electricity

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xx.arianagrande
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#1
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#1
In the equation V = IR, when I increases, R decreases so V should remain constant, right? But when R increases, V decreases and vice versa, so why is that?
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SagaciousSag
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#2
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#2
V increases.
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xx.arianagrande
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#3
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#3
(Original post by SagaciousSag)
V increases.
what?
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Sinnoh
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#4
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(Original post by xx.arianagrande)
what?
It depends on what's being kept constant. Saying that I increases and R decreases is only the case if V is being kept constant.
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xx.arianagrande
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#5
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#5
(Original post by Sinnoh)
It depends on what's being kept constant. Saying that I increases and R decreases is only the case if V is being kept constant.
Then in what case would V increase as R decreases?
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Sinnoh
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#6
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#6
(Original post by xx.arianagrande)
Then in what case would V increase as R decreases?
This would be if you were somehow rapidly increasing the current, but that doesn't really make much sense in this context. The devices you'd encounter in circuits in GCSE would generally have a specific value of potential difference (for a given circuit configuration); the only way to modify it would be to change the voltage of the battery or by adding more components in the circuit.
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xx.arianagrande
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#7
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#7
(Original post by Sinnoh)
This would be if you were somehow rapidly increasing the current, but that doesn't really make much sense in this context. The devices you'd encounter in circuits in GCSE would generally have a specific value of potential difference (for a given circuit configuration); the only way to modify it would be to change the voltage of the battery or by adding more components in the circuit.
But I got an exam question which mentioned V increasing as R decreases?
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AlanT12
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#8
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#8
(Original post by xx.arianagrande)
But I got an exam question which mentioned V increasing as R decreases?
Post the full wording of the question.
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Sinnoh
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#9
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#9
(Original post by xx.arianagrande)
But I got an exam question which mentioned V increasing as R decreases?
This could be the case with multiple components in the circuit, i.e. a potential divider (more of that in A-level)
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xx.arianagrande
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#10
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#10
(Original post by AlanT12)
Post the full wording of the question.
Q04.6 https://filestore.aqa.org.uk/sample-...F-QP-NOV20.PDF

The answers should be decreases, decreases
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Ethanity007
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#11
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#11
The emf of battery is assumed to be constant. When u increase the number of resistor in the ckt, effective resistance increases and thus the current flowing in the ckt decreases. The potential difference across each resistor (p.d = IR) thus decreases
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xx.arianagrande
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#12
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#12
(Original post by Ethanity007)
The emf of battery is assumed to be constant. When u increase the number of resistor in the ckt, effective resistance increases and thus the current flowing in the ckt decreases. The potential difference across each resistor (p.d = IR) thus decreases
? what is emf
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vapordave
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#13
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#13
(Original post by xx.arianagrande)
? what is emf
It means potential difference/voltage (not quite but you don't need to know the difference for GCSE)
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xx.arianagrande
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#14
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#14
(Original post by Ethanity007)
The emf of battery is assumed to be constant. When u increase the number of resistor in the ckt, effective resistance increases and thus the current flowing in the ckt decreases. The potential difference across each resistor (p.d = IR) thus decreases
Then what is the relationship between V, I and R? e.g. As I increases, R decreases etc.?
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xx.arianagrande
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#15
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#15
(Original post by vapordave)
It means potential difference/voltage (not quite but you don't need to know the difference for GCSE)
Thanks
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mustz__
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#16
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#16
(Original post by xx.arianagrande)
In the equation V = IR, when I increases, R decreases so V should remain constant, right? But when R increases, V decreases and vice versa, so why is that?
No, Resistance will always be constant in GCSE physics from what I remember, So V is directly proportional to I, therefore V increases means I increases and vice versa
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xx.arianagrande
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#17
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#17
(Original post by mustz__)
No, Resistance will always be constant in GCSE physics from what I remember, So V is directly proportional to I, therefore V increases means I increases and vice versa
I thought resistance can increase/decrease?
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Ethanity007
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#18
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#18
Resistance of an ohmic resistor will be a constant (if qn say a resistor… we assume this resistor has constant resistance.

For your questions, they are more resistors connected in series. So the effective resistance of the whole ckt increases.
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Ethanity007
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#19
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#19
For non ohmic resistor like thermistor or LDR (light dependant resistor), their resistance changes when temperature and light intensity changes respectively. Temperature/intensity increases, resistance decreases and vice versa.

For light bulb, as the temperature increses, its resistance increases.
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xx.arianagrande
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#20
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#20
(Original post by Ethanity007)
Resistance of an ohmic resistor will be a constant (if qn say a resistor… we assume this resistor has constant resistance.

For your questions, they are more resistors connected in series. So the effective resistance of the whole ckt increases.
ok so for my question, we assume this resistor has constant resistance because it is an ohmic resistor? But then what do you mean by the resistance increasing?
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