Question

The above circuit is a part of an electrical device. Use the information given in the question to calculate the following. 

(i) Potential Difference across R2. 

(ii) Value of the resistance R2. 

(iii) Value of resistance R1

Answer 1

(i) p.d. across 4 Ω resistor = p.d. Across R2 as both are in parallel. 

1.5 (A) × 4 (Ω) = 6 V 

(ii) Total Current through 4 Ω and R2 = 2.0 A (given)

Current through 4 Ω = 1.5 A (given) 

Hence current through R₂ = 2-1.5= 0.5 A 

Using Ohm’s law for R₂ we get 

6 V= 0.5 A x R₂ 

Hence R₂ = 6/0.5 = 12 Ω 

(iii) p.d. across R1 = Total p.d. - (p.d. across R2) - (p.d. across 2.0 Ω)

p.d. across 2.0 Ω = 2x2 = 4 V 

p.d. across R2 = 6 V (calculated before) 

Hence p.d. across R₁ = 12 − 6 − 4 = 2V 

Current through R₁ = 2A 

Using Ohm’s Law, 

we get R₁ = 2V/2A = 1Ω