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Question
In the figure below, the ammeter A reads 0.3 A. Calculate:
(i) the total resistance of the circuit
(ii) the value of R
(iii) the current flowing through R.
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Solution
(i) ∵ V = IR
∴ R = `"V"/"I" = 6.0/0.3 = 20 Ω`
(ii) Total resistance = 20 Ω
∵ Resistance in parallel
∴ `1/20 = 1/"R" + 1/60`
`1/"R" = 1/20 - 1/60`
`1/"R" = (3 - 1)/60`
R = `60/2 = 30 `Ω
(iii) ∵ V = IR
and potential (V) is equal at the two ends i.e. A and B
Let I1 be current flowing through R
∴ (0.3 - I1) is current flowing through 60 Ω resistance.
Now V = V ⇒ I1R1 = I2R2
I1 × 30 = (0.3 - I1) × 60
I1 = 0.6 - 2I1
3I1 = 0.6
I1 = `0.6/3 = 0.2`
∴ Current flowing through R = 0.2 A
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