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The resistance of a 10 m long wire is 20 Ω. It is connected in series with a 3 V battery and a 10 Ω resistor. The potential difference between two points on the wire separated by a distance of 30 cm is equal to ______.

Asked in RS Academy GUJCET booklet · Kirchhoff's laws in networks

• (1) 0.02 V
• (2) 0.06 V
• (3) 0.1 V
• (4) 1.2 V

Step-by-step solution

Why the other options are wrong

• (1) No single slip produces 0.02 V. Sanity check: the wire drops 0.1×20 = 2 V over 10 m, i.e. 0.2 V per metre, so 0.30 m of it drops 0.06 V.
• (3) This is the current, I = 3/(20 + 10) = 0.1 A, written as a voltage. The voltage across 30 cm of wire is I times that piece's resistance, 0.1×0.6 = 0.06 V.
• (4) No single slip produces 1.2 V. Sanity check: the whole 10 m wire drops only 2 V, so a 30 cm piece must drop far less than 1.2 V.

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