Based on Fig 18.5, calculate: (i) the total resistance in the circuit (ii) the current flowing through each resistor.
12 V
1 R 1
R1
1 R2
Derivation: Based on: The potential difference between two points is the same regardless of the path followed. The potential difference across each of the resistances from A to B is V.
[since :Ohm’s law] [by dividing by V ]
I V R
60 50 30 Fig 18.5 SAMPLE ANSWER 18C
(i) Using the formulae for Resistance in series and Resistance in parallel, making sure all values are in their standard unit:
1 RP 1 RP
1 R2
1 R3
1 60 1
30 1
R 20 50 70 R R1 RP
, where RP resistance in the parallel part of the circuit, R2 60 and R3 30 . 60 2
60 3 60 1 20QRP 20 , where R total resistance and R1 50 . The total resistance is 70 .
(ii) Using Ohm’s law, making sure all values are in their standard unit: The current flowing through the 50 resistor is
