A 5 V battery is connected to two 20 Ω resistors which are joined together in series.

(a) Draw a circuit diagram to represent this. Add an arrow to indicate the direction of conventional current flow in the circuit.
(b) What is the effective resistance of the two resistors?
(c) Calculate the current that flows from the battery?
(d) What is the p.d. across each resistor?

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Solution

(a) Circuit diagram

(b) Since two resistors of 20 Ω are connected in series, the effective resistance will be
R = R₁+ R₂
Here, R₁=20 Ω,
R₂ =20 $Ω$
Therefore,
R = 20 Ω + 20 Ω = 40 $Ω$
The effective resistance of the two resistors, R= 40 Ω
(c) The current that flows from the battery,
I = V / R
I = 5 / 40
I = 0.125 A

(d) The p.d. across the 20 Ω resistor, V= I $\times$ R
V = 20 x 0.125 V
V = 2.5 V
Similarly, the potential difference across the second 20 Ω resistor is equal to 2.5 V.

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