Magnetism & Electromagnetism - 7.3.1 Induced Potential (HT Only) (GCSE Physics AQA)

Induced Potential (HT Only)

The Generator Effect

• When we move a magnet around a coil of wire, we will produce a potential difference. This is known as electromagnetic induction. We have created a voltage using a changing magnetic field
• You can also create the voltage by moving the wire around the magnet (and keeping the magnet still). If the wire is part of a complete circuit, a current is generated in a process called the generator effect.

Effects of the induced Current

• Induced currents create magnetic fields. An induced current is one which is due to a change in magnetic field, so this means that we are left with two magnetic fields: The original one and the second one which has been produced.
• The magnetic field that we have created will always oppose the change that made it in the first place. For example, if the magnetic field was created due to the movement of a wire, then the magnetic field that we have created will oppose this movement.

Factors Affecting the Size of the Induced Current/PD

There are three factors affecting the size of the induced current or potential difference:

1. Moving the magnet faster. By moving the magnet faster, we are able to ‘cut’ more field lines in the same amount of time. Since a higher number of field lines means a stronger magnetic field, we are able to increase the size of the induced current and voltage.
2. Using a stronger magnet. Stronger magnets have a higher magnetic flux density compared to weaker magnets. A higher magnetic flux density means that there are more magnetic field lines around the magnet. This means that more of these field lines will be cut, so the induced current and voltage will be bigger.
3. Increasing the number of turns on the coil. By increasing the number of turns on a wire, we are increasing the magnetic flux density of the magnet. In earlier tutorials, we discussed that solenoids make electromagnets stronger due their coil shape.

Factors Affecting the Direction of the Induced Current/PD

There are two factors affecting the direction of the induced current or potential difference:

1. Reversing the wire/coil direction. When we reverse the direction of wire or coils movement, then we will be reversing the induced current or induced pd that we generate.
2. Reversing the magnet. When we reverse the polarity of the magnet, this has the same effect as reversing the coil direction – the induced current / pd will be reversed too.

Applying the Generator Effect

We have been describing the generator effect in this section, but for AQA exams it is important that you are able to apply it in a given context.

Here, we will explore it in relation to a bike light.

1. Pedalling will cause rotation. When a cyclist pedals their bike, they will rotate the tyres. The back tyre will touch a small magnet inside a coil. The coil begins to rotate.
2. The coil will induce a current. When the coil rotates, it will induce a current. This will generate electricity, which can be used to power the lights of the bike.