Which one of the following laws of electromagnetism does not give the direction of magnetic field ?

The correct answer is D, Faraday's law of electromagnetic induction. Faraday's law is a law of magnitude, not a direction rule. It states that the emf induced in a circuit is proportional to the rate at which the magnetic flux through it changes. It tells how large the induced emf is, but it says nothing about which way the magnetic field points; the direction of the induced current comes from Lenz's law. The three other options are hand rules, and each one links the direction of the magnetic field with other directions. Option A is wrong because the right-hand thumb rule directly gives the direction of the magnetic field lines around a straight current-carrying wire: the thumb along the current, the curled fingers along the field. Option B is wrong because in Fleming's left-hand rule the forefinger shows the field, the middle finger the current and the thumb the force on a conductor, as in a motor. Option C is wrong because in Fleming's right-hand rule the forefinger again marks the field, with the thumb for motion and the middle finger for induced current, as in a generator. Exam tip: Faraday gives how much emf, Lenz gives which way; left hand for motors, right hand for generators.