Join TSR now and get all your revision questions answeredSign up now
    • Thread Starter
    Offline

    0
    ReputationRep:
    Okay, I feel like I'm being really stupid, but I've just completely lost the ability to find the current in a circuit.

    The question is:
    In a circuit of total e.m.f 4.5V, and 2 resistors of 68 Ohms and 12 Ohms, calculate the current in th2 12 Ohm resistor.

    I know I = V/R and everything, but is the V the total e.m.f? And is the resistance the total resistance or just the resistance of the 12 Ohm resistor?

    If anyone can help, it would be much appreciated.

    Thanks!
    Offline

    3
    ReputationRep:
    (Original post by lucy_henley)
    Okay, I feel like I'm being really stupid, but I've just completely lost the ability to find the current in a circuit.

    The question is:
    In a circuit of total e.m.f 4.5V, and 2 resistors of 68 Ohms and 12 Ohms, calculate the current in th2 12 Ohm resistor.

    I know I = V/R and everything, but is the V the total e.m.f? And is the resistance the total resistance or just the resistance of the 12 Ohm resistor?

    If anyone can help, it would be much appreciated.

    Thanks!
    It depends on whether the circuit is in series or parallel.
    Offline

    0
    ReputationRep:
    (Original post by lucy_henley)
    Okay, I feel like I'm being really stupid, but I've just completely lost the ability to find the current in a circuit.

    The question is:
    In a circuit of total e.m.f 4.5V, and 2 resistors of 68 Ohms and 12 Ohms, calculate the current in th2 12 Ohm resistor.

    I know I = V/R and everything, but is the V the total e.m.f? And is the resistance the total resistance or just the resistance of the 12 Ohm resistor?

    If anyone can help, it would be much appreciated.

    Thanks!
    Has it told you anything about the internal resistance (r)? Or has it only given you the load resistance (R)?


    This was posted from The Student Room's iPhone/iPad App
    • Thread Starter
    Offline

    0
    ReputationRep:
    It's a series circuit, and there's negligible internal resistance, only the external resistors
    Offline

    3
    ReputationRep:
    (Original post by lucy_henley)
    It's a series circuit, and there's negligible internal resistance, only the external resistors
    In series current is constant.
    Offline

    2
    ReputationRep:
    I = V/R

    For a circuit, to find Is (the source current) you'll want to use the source voltage and the total equivalent resistance of the circuit. If there are other sources, IT = VT/RT (total current, voltage and equivalent resistances).

    For a series circuit, Rt (total resistance) = R1 + R2 + R3...

    For a series circuit, voltage (potential differences) are shared between components, but the current is the same. For a parallel circuit the opposite is true - The voltage is the same for each parallel loop and the current is shared between components across other loops.


    Does this help you to work it out now?
 
 
 
Poll
If you won £30,000, which of these would you spend it on?

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Quick reply
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.