Electromagnetic Induction (Topic 13)

Everything on the checklist for Electromagnetic Induction (Topic 13)

What is Electromagnetic Induction?

INDUCTION of a POTENTIAL DIFFERENCE (+ Current if a Complete Circuit) across a WIRE which is EXPERIENCING A CHANGE in an EXTERNAL MAGNETIC FIELD

What are the Two Ways to Induce a Potential Difference in a Wire?

• MOVE THE WIRE in a MAGNETIC FIELD

• MOVE/CHANGE the MAGNETIC FIELD around a WIRE

How to Switch the Direction of an Induced Potential Difference?

• MOVE WIRE in OPPOSITE DIRECTION

• SWAP POLES OF MAGNET

What are the Three Factors that affect the Size of the Induced Potential Difference?

• SPEED OF MOVEMENT

• STRENGTH OF MAGNETIC FIELD

• TURNS ON COIL

How does a Alternator Work?

1. COIL of Wire (free to rotate) is placed in a MAGNETIC FIELD

2. COIL is SPUN in ONE DIRECTION → CURRENT PRODUCED

3. EVERY HALF TURN (e.g when Vertical), the CURRENT DIRECTION SWAPS (because Side of Coil which was moving Up is now moving Down) → INDUCES AC CURRENT

4. SLIP RINGS + BRUSHES make sure the CONTACTS DON’T SWAP

How does a Dynamo Work?

1. COIL of Wire (free to rotate) is placed in a MAGNETIC FIELD

2. COIL is SPUN

3. EVERY HALF TURN (e.g when Vertical), the SPLIT RING COMMUTATOR SWITCHES the CONTACTS of the Loop

4. → INDUCES DC CURRENT

How is Electricity Generated on Large Scales?

1. FUELS BURNT to HEAT WATER

2. STEAM PRODUCED

3. STEAM TURNS TURBINE which is in a MAGNET → INDUCES AC CURRENT

How does a Microphone Work?

1. SOUND WAVES hit a DIAPHRAGM which is attached to a COIL

2. COIL MOVES BACK AND FORTH → INDUCES AC CURRENT

How do Transformers Work?

1. AC CURRENT flows through PRIMARY COIL → Produces CHANGING MAGNETIC FIELD in the PRIMARY COIL

2. CHANGING MAGNETIC FIELD LINES CUT the SECONDARY COIL → INDUCES a ALTERNATING POTENTIAL DIFFERENCE

3. If Secondary Coil is in a COMPLETE CIRCUIT → AC CURRENT INDUCED

What is Way to make Transformers more Efficient?

Wrap PRIMARY + SECONDARY COIL around an IRON CORE → TRANSFERS ALTERNATING MAGNETIC FIELD from PRIMARY to SECONDARY COIL

What are the Two Types of Transformers?

• STEP-UP Transformer → MORE COILS on Secondary Coil → INCREASES POTENTIAL DIFFERENCE

• STEP-DOWN Transformer → LESS COILS on Secondary Coil → DECREASES POTENTIAL DIFFERENCE

What is the Equation for Potential Difference in Transformers?

V₁ / V₂ = N₁ / N₂

VOLTAGE across PRIMARY COIL / VOLTAGE across SECONDARY COIL = NUMBER OF TURNS on PRIMARY COIL / NUMBER OF TURNS on SECONDARY COIL

What are the Two Reasons that Transformers are 100% Efficient?

• ALL FIELD LINES PASS through BOTH COILS

• NO ENERGY is WASTED THROUGH HEATING

What is the Equation for Current + Potential Difference in Transformers?

V₁ x I₁ = V₂ x I₂

VOLTAGE x CURRENT in PRIMARY COIL = VOLTAGE x CURRENT in SECONDARY COIL

What is the Order of Steps in the National Grid?

1. POWER STATION

2. STEP-UP TRANSFORMER to 400,000V

3. ELECTRICITY CABLES

4. STEP-DOWN TRANSFORMER to 230V

5. CONSUMERS

Why is Electricity’s Potential Difference Increased when travelling across the National Grid?

1. P = I² x R, where P = ENERGY WASTED DUE TO HEATING + R = RESISTANCE OF WIRES (Already low) → We want CURRENT to be LOW

2. V₁ x I₁ = V₂ x I₂ → STEP-UP TRANSFORMER to make CURRENT LOW + VOLTAGE HIGH