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If 20 J of work has to be done to move an electric charge of 4 C from a point where the potential is 10 V to another point where the potential is V volt, find the value of V.

Asked in GUJCET 2008 · Work done in moving a charge

• (1) 5 V
• (2) 15 V
• (3) 2 V
• (4) 70 V

Step-by-step solution

Why the other options are wrong

• (1) Stops at W/q=5 V, which is the potential difference, not the final potential (or subtracts it from 10 V). Positive work done on a positive charge carries it up in potential: 10+5=15 V.
• (3) No single slip gives 2 V. Sanity check: V-10=(20)/4=5, so V=15 V.
• (4) No single slip gives 70 V: it needs W multiplied by q and the sign reversed as well, |10-20×4|. Sanity check: V=10+(20)/4=15 V.

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