The induced current in a coil always flows in a direction so as to oppose the change that causes it. This statement is known as

Step 1: Analyze the question The statement says the induced current flows in a direction that opposes the change producing it. We need the law that describes this.

Step 2: Explain the concept When the magnetic flux through a coil changes, an e.m.f. and current are induced. Two laws are involved:

• Faraday's law gives the size of the induced e.m.f.: it is proportional to the rate of change of magnetic flux linkage.
• Lenz's law gives the direction of the induced current: it flows so as to oppose the change in flux that produced it.

This is a consequence of conservation of energy. If the induced current aided the change, energy would be created from nothing.

Combined, the two laws give:

E = −N (dΦ/dt)

The negative sign is Lenz's law.

Step 3: Eliminate the options

• A. Coulomb's law: concerns the force between electric charges. Not relevant.
• B. Lenz's law: states that the induced current opposes the change causing it. This matches.
• C. Faraday's law: gives the magnitude of the induced e.m.f., not the direction.
• D. Ampere's law: relates a magnetic field to the current producing it. Not relevant.

Step 4: Answer The correct option is B. Lenz's law.

Exam tip: Remember "Lenz = Location/direction (opposes)" and "Faraday = Figure/amount (magnitude)". Whenever you see the words "opposes the change," think Lenz.