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.

Answer 1

(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