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PhysicsJAMB UTME2002

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Earlier discussion

1 older comment kept for context.

Oluwaseun Adeyemi

Let the combined parallel resistance of 3 Ω and x = Q Ω

∴ Total resistance in the circuit = 2 + Q + 1.5 = 3.5 + Q Ω

Total current in the circuit = 2A

P.D a cross the circuit 12 volts

∴ From Ohm’s law, V = IR

12 = 2(3.5 + Q)

= 7.0 + 2Q

∴ 2Q = 12 – 7

= 5

∴ Q = 5/2 = 2.5 Ω

Thus from parallel formula: I/Q = 1/3 + 1/x
1/2.5 = 1/3 + 1/x

∴ 1/x = 1/2.5 - 1/3 = 3-2.5/7.5 = 0.5/7.5

X = 7.5/0.5 = 75/5 = 15 Ω

∴ X = 15 Ω