Ohm’s law: connect voltage, current and resistance

Know the condition as well as the formula

NCERT describes potential difference as proportional to current for a given metallic wire when its temperature remains the same. The constant ratio V/I is its resistance, R. Resistance is measured in ohms.

The condition matters: the formula should not be presented as proof that every device has the same constant resistance under every possible condition. Identify the component and assumptions in the question.

An original worked example

Suppose an ideal classroom resistor has resistance 6 ohms and a potential difference of 18 volts. The current is I = V/R = 18/6 = 3 amperes. These are invented teaching values, not a measurement from an actual household circuit.

If the voltage remains 18 volts while resistance becomes 12 ohms, the current becomes 1.5 amperes. The comparison changes one quantity at a time, making the inverse relationship easier to see.

Avoid a symbol-only answer

Write what is known before substituting numbers. If current is requested, rearrange to I = V/R; if resistance is requested, use R = V/I. Include units at each step so that a numerical answer retains its physical meaning.

An original practice task is to create three versions of the same problem, hiding a different quantity each time. Solve them and check by substituting the result back into V = IR. This tests the relationship rather than memorisation of one example.

This is a paper-based educational calculation, not instructions to open or test mains-powered equipment. A simplified resistor problem cannot establish whether an actual installation is safe. The linked textbook provides the school-level context for the law and its stated condition.

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