NSC / Matric Electrodynamics — practice questions

1. A generator has a coil that is turned inside a magnetic field by some outside machine. 2. Turning the coil changes the magnetic flux through it, which induces an emf. 3. So the motion supplied to the coil is converted into electrical energy. 4. The reverse conversion, electrical into mechanical, is what an electric motor does. _Source: Siyavula Physical Sciences Grade 12 (Everything Science, CC BY 4.0), Chapter 11: Electrodynamics_

1. Both machines have the same coil turning in the same magnetic field. 2. In the coil itself the current reverses every half turn in both machines. 3. An alternating current generator uses two slip rings, so that reversal reaches the outside circuit. 4. A direct current generator uses one ring split into two pieces, called a commutator. 5. The split ring swaps contacts at the same instant the current reverses so the outside circuit always receives current in one direction, which is why removing the brushes cannot be the answer. _Source: Siyavula Physical Sciences Grade 12 (Everything Science, CC BY 4.0), Chapter 11: Electrodynamics_

1. Transformers work on a changing magnetic flux, so they only work with alternating current. 2. That lets the voltage be stepped up to a very high value at the power station. 3. High voltage means low current for the same power, and low current means little energy lost as heat in the lines. 4. The voltage is then stepped down again close to the buildings that use it. 5. Alternating current still needs conductors and it still heats a resistor, which rules out the last two options. _Source: Siyavula Physical Sciences Grade 12 (Everything Science, CC BY 4.0), Chapter 11: Electrodynamics_