Electromagnetic induction

Question 1

How is a voltage induced in a conductor or coil?

Answer 1

• A voltage is induced when a conductor moves through a magnetic field or when the magnetic field changes.
• This process is known as electromagnetic induction.
• The size of the induced voltage depends on:
  
  • Speed of movement – Faster movement produces a greater voltage.
  • Strength of the magnetic field – Stronger fields induce larger voltage.
  • Number of coils – More turns increase the induced voltage.
• If the conductor is part of a closed circuit, a current flows (Faraday’s Law).
• Used in generators, transformers, and induction cookers.

Question 2

What factors affect the size of the induced voltage?

Answer 2

• Increasing speed of movement – Faster motion induces a larger voltage.
• Using a stronger magnet – Stronger fields produce a greater rate of change of flux.
• Increasing number of coils in a solenoid – More turns induce a larger total voltage.
• Changing the magnetic field more rapidly – Faster flux changes result in higher induced voltage.
• Orientation of movement – Maximum voltage is induced when motion is perpendicular to the field lines.

Question 3

How does a rotating magnet induce electricity in a coil?

Answer 3

• A magnet rotates inside a coil, causing the magnetic field through the coil to change continuously.
• This changing field induces an alternating voltage (A.C.) due to Faraday’s Law.
• If the coil is connected to a circuit, a current flows.
• The size of the induced voltage depends on:
  
  • Strength of the magnet – Stronger magnets induce more voltage.
  • Speed of rotation – Faster rotation increases voltage and frequency.
  • Number of turns in the coil – More turns increase voltage.
• Used in power station generators to produce electricity.

Question 4

How does a coil rotating in a magnetic field generate electricity?

Answer 4

• A coil of wire rotates inside a fixed magnetic field.
• The motion causes the magnetic flux to change, inducing a voltage.
• The induced voltage is alternating (A.C.), as different sides of the coil cut the field in opposite directions.
• Faster rotation results in higher voltage and frequency.
• The induced voltage follows a sinusoidal waveform, producing alternating current.
• Used in alternators, wind turbines, and hydroelectric generators.

Question 5

What is the structure of a transformer?

Answer 5

• A transformer consists of:
  
  • Primary coil – Receives an alternating current (A.C.).
  • Soft iron core – Concentrates and transfers the magnetic field.
  • Secondary coil – Where the changing field induces a voltage.
• The A.C. in the primary coil creates a changing magnetic flux in the iron core.
• This induces a voltage in the secondary coil due to electromagnetic induction.
• The turns ratio determines if the transformer is step-up or step-down.

Question 6

How do step-up and step-down transformers work?

Answer 6

• Step-up transformers: Increase voltage (more turns on secondary coil than primary).
• Step-down transformers: Decrease voltage (fewer turns on secondary coil than primary).
• Used in electricity transmission to reduce energy loss by increasing voltage and decreasing current.
• Step-up transformers: Used at power stations to increase voltage before transmission.
• Step-down transformers: Used in homes and factories to reduce voltage to a safe level.
• Efficient transformers make electricity distribution economical.

Question 7

What is the transformer turns ratio equation?

Answer 7

• The equation is: Vp / Vs = Np / Ns
  
  • Vp = primary voltage (V)
  • Vs = secondary voltage (V)
  • Np = number of turns on primary coil
  • Ns = number of turns on secondary coil
• Determines if a transformer is step-up or step-down:
  
  • If Ns > Np, the transformer is step-up.
  • If Ns < Np, the transformer is step-down.

Question 8

What is the power equation for an ideal transformer?

Answer 8

• For 100% efficiency, input and output power are equal: Vp Ip = Vs Is
  
  • Vp = primary voltage (V)
  • Ip = primary current (A)
  • Vs = secondary voltage (V)
  • Is = secondary current (A)
• If voltage increases, current must decrease to conserve power.
• In reality, transformers are not 100% efficient due to heat loss and eddy currents.
• Used in power grids and appliances to manage voltage efficiently.