Electromagnetic induction in transformers (Edexcel GCSE Physics): Revision Notes
Electromagnetic induction in transformers
Electromagnetic induction happens when a changing magnetic field creates electricity in a wire. This is how transformers work — they use this idea to change the voltage of electricity, either making it higher (step-up) or lower (step-down).
- Transformers help transmit electricity over long distances and make it safe for use in homes.
How Electromagnetic Induction Works
Electromagnetic induction happens when a magnetic field and an electrical conductor (like a wire) move relative to each other. This means the magnetic field around the wire changes, which creates a potential difference (voltage). If the circuit is complete, this makes an electric current flow.
Ways to Create Electromagnetic Induction:
- Move a magnet near a coil of wire. As the magnet moves, it changes the magnetic field around the wire, inducing a voltage.
- Rotate the magnet or wire. If the magnet or wire spins, the magnetic field changes continuously, creating an alternating current (AC).
- Reverse the direction of movement or flip the magnet's poles. This reverses the current.
Opposition to the Change
When a current is induced in a wire, the current creates its own magnetic field. This new magnetic field opposes the change that caused it, acting as a resistance to the movement that generated the current.
Transformers – How They Work
Transformers consist of:
- Primary coil: The coil where alternating current (AC) flows in.
- Secondary coil: The coil where the transformed voltage comes out.
- Iron core: A soft iron core links the magnetic field between the two coils and ensures efficient transfer of energy.
When AC flows into the primary coil, it creates a changing magnetic field. This magnetic field passes through the iron core and induces a voltage in the secondary coil through electromagnetic induction.
Step-Up and Step-Down Transformers
- Step-Up Transformer: Increases the voltage by having more turns of wire in the secondary coil than the primary coil. This type is used to send electricity efficiently over long distances.
- Step-Down Transformer: Decreases the voltage by having fewer turns of wire in the secondary coil. It makes electricity safe for use in homes and devices.
You can increase the induced voltage by:
- Increasing the strength of the magnetic field.
- Moving the magnet or wire faster.
- Adding more turns of wire in the coil.
Efficiency of Transformers
In real-life applications, transformers are highly efficient, but they are not 100% efficient. Some energy is lost as heat in the coils and the core. Despite this, most energy is transferred between the coils, making transformers vital for power transmission.
Real-Life Example: Power Lines
Electricity is generated at low voltage. Step-up transformers increase the voltage so electricity can travel through power lines without losing much energy. When the electricity reaches homes, step-down transformers lower the voltage to make it safe for devices like lights and chargers.