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Electricity & Electromagnetism · Part 3 of 3
9 exam-style questions with model answers, plus 12 quick multi-choice questions — every question on this part of the standard, grouped by the 3 pages of notes they come from.
Write a full answer before you reveal the model one. That comparison is where the learning happens.
A wire of length m carries a current of A at right angles to a magnetic field of T.
Calculate the force on the wire.
A straight wire carrying a current of A lies in a magnetic field of T. The length of wire in the field is cm.
Calculate the force on the wire when the current is perpendicular to the field. State and explain what the force would be if the wire were rotated so that the current ran parallel to the field.
A simple DC motor consists of a rectangular coil of turns, each of length cm along the sides that lie in the field, carrying a current of A in a magnetic field of T.
Calculate the force on one side of the coil. Explain fully why the coil rotates rather than moving in a straight line, and explain the purpose of the split-ring commutator and what would happen without it.
A charge of C moves at m s−1 perpendicular to a magnetic field of T.
Calculate the force on the charge.
An electron enters a uniform magnetic field at right angles to the field lines and follows a circular path.
Explain why the path is circular, and explain why the electron's speed does not change while it is in the field.
An electron and a proton, both travelling at m s−1, enter the same uniform magnetic field of T at right angles to the field, moving in the same direction.
Calculate the radius of each particle's circular path. Explain fully why they curve in opposite directions, and compare what would happen if they instead entered a uniform electric field.
A conductor m long moves at m s−1 perpendicular to a magnetic field of T.
Calculate the voltage induced across the conductor.
A metal rod is moved at a steady speed across a uniform magnetic field, and a voltage is measured across its ends.
Explain how this voltage is produced. State two changes that would increase it, and state what happens if the rod is instead moved parallel to the field lines.
A student moves a conducting rod across a magnetic field, first with the rod's ends unconnected, then with the ends connected by a wire to form a complete circuit. They notice that the rod is noticeably harder to push in the second case.
Explain fully why a voltage is induced, why a current flows only in the second case, and why the rod becomes harder to push. Refer to energy conservation in your answer.