## December 18, 2011

### Topic 6

Magnetism and Electromagnetism
Objectives:
6b) Magnetism
6.2 recall that magnets repel and attract other magnets, and attract magnetic substances
6.3 recall the properties of magnetically hard and soft material
6.4 understand the term ‘magnetic field line’
6.5 understand that magnetism is induced in some materials when they are placed in a magnetic field
6.6 sketch and recognise the magnetic field pattern for a permanent bar magnet and that between two bar magnets
6.7 know how to use two permanent magnets to produce a uniform magnetic field pattern

6c) Electromagnetism
6.8 recall that an electric current in a conductor produces a magnetic field round it
6.9 describe the construction of electromagnets
6.10 sketch and recognise magnetic field patterns for a straight wire, a flat circular coil and a solenoid when each is carrying a current
6.11 appreciate that there is a force on a charged particle when it moves in a magnetic field as long as its motion is not parallel to the field
6.12 recall that a force is exerted on a current-carrying wire in a magnetic field, and how this effect is applied in simple d.c. electric motors and loudspeakers
6.13 use the left hand rule to predict the direction of the resulting force when a wire carries a current perpendicular to a magnetic field
6.14 recall that the force on a current-carrying conductor in a magnetic field increases with the strength of the field and with the current.

6d) Electromagnetic induction
6.15 recall that a voltage is induced in a conductor or a coil when it moves through a magnetic field or when a magnetic field changes through it; also recall the factors which affect the size of the induced voltage
6.16 describe the generation of electricity by the rotation of a magnet within a coil of wire and of a coil of wire within a magnetic field; also describe the factors which affect the size of the induced voltage
6.17 recall the structure of a transformer, and understand that a transformer changes the size of an alternating voltage by having different numbers of turns on the input and output sides
6.18 explain the use of step-up and step-down transformers in the large-scale generation and transmission of electrical energy
6.19 recall and use the relationship between input (primary) and output (secondary) voltages and the turns ratio for a transformer:
$\frac{input\, (primary)\, voltage}{output\, (secondary)\, voltage}=\frac{primary\: turns}{secondary\: turns}$
6.20 recall and use the relationship (for 100% efficiency):