A current of 1 ampere flows in a series circuit containing an electric lamp and a conductor of 5 Ω when connected to a 10 V battery. Calculate the resistance of the electric lamp. Now if a resistance of 10 Ω is connected in parallel with this series combination, what change (if any) in current flowing through the 5 Ω conductor and potential difference across the lamp will take place? Give reason.
Explanation:-
Current, I = 1A
Resistance of conductor, RC = 5
Voltage, V = 10V
Resistance of lamp, RL =?
Total resistance in the circuit, RT = V/ I = (10/1) = 10
The situation can be depicted as:
As the resistances are in series, RT = RC + RL
RL = 10 – 5= 5
Potential difference across the lamp = I RL = (1 × 5) = 5V
Now, 10Ω resistance is connected in parallel with total resistance RT
1/Rnew = (1/10) + (1/10) = 2/10 = 1/5
Rnew = 5
New current, Inew = V/Rnew = (10/5) A = 2 A
As both branches have equal resistance, current will divide equally.
Hence, current through 5Ω resistance and lamp = 2/2 = 1 A.
Potential difference across the lamp = 1 × 5 = 5 V.
There will be no change in the current flowing through 5-ohm conductor and potential difference across the lamp. As voltage remains the same in both the branches the potential difference across the lamp will also remain the same.