P6 - Electromagnetism

P6 - Electromagnetism

1. Definition

   • Current carrying wire produces a magnetic field Direction of magnetic field given by right hand rule Thumb = direction of current grip = direction of MF

2. Strength of Field

   • Depends on : Current Coils of wire Iron core used

3. Solenoid

4. Use of Electromagnets

   • Circuit Breakers Particle Accelerators Scrapyard Cranes Bells and speakers

5. Motor Effect

   • The force experienced by a current carrying wire in a magnetic field
   • Left Hand Rule
     • Used to figure out direction of a certain thing Thumb = Force Forefinger = Magnetic field Middle Finger = Current
   • Affecting Force
     • Increase strength of magnetic field Increase current 

6. DC Motors

   • Utilises direct current to create power - motor to electric  Movement of wire through magnetic field results in electrons being excited and moving
   • Split Ring Commutator
     • Used to flip the direction of current every half turn to ensure direction of force is constant to allow constant rotation
   • Increasing Force or Output
     • More coils Stronger magnetic field Soft iron core More current

7. Electromagnetic Induction

   • Causing a current in a wire due to a magnetic field
   • Right Hand Rule
     • Gives direction of current Thumb : Force Forefinger : Direction magnetic field Middle finger : Direction of current
   • Affecting Induced Current
     • Increase by increasing speed at which coils cut magnetic field lies Stronger magnetic field More coils
   • AC Generator
     • Armature causes circuit to cut through magnetic field lines, inducing a current.  Current varies as the circuit becomes parallel, and goes back to cutting lines
     • Slip Ring
       • Completes the circuit with carbon brushes and remains in contact with them, allowing electricity to flow
     • AC Current
       • After every half turn, the field is cut in the opposite direction, flipping the direction of current, making it ALTERNATE

8. Transformers

   • Device used to increase or decrease current for transmission and usage Only works with AC current, due to requirement of inducing current in other coil
   • Step Up
     • Makes voltage extremely high for transmission More secondary coils than primary coils
   • Step Down
     • Brings voltage down from transmission for commercial usage Primary coils more than secondary coils
   • Reason for Use
     • Decreases energy loss for long distance transport - V>I so less I, I^2R=Power Loss Less energy lost through heat, as each electron carries more voltage, but less electrons present
   • Requirements
     • Two sets of coils - Primary + Secondary Soft iron core - laminated to reduce heat loss
   • Formula
     • Np/Ns = Vp/Vs No of coils Primary/Secondary = Voltage Primary/Secondary

9. Energy Sources

   • All energy sources except nuclear and geothermal depend on the sun
   • Renewable
     • Continuous and won't run out - Solar, Geothermal, Biomass
     • Wind
       • Positives - clubbed with other renewable sources(solar), renewable Negatives - inefficient, visual and noise pollution, cost, area specific
     • Hydroelectric
       • Negatives : Setup cost, damages environment, area specific Positives : Same as wind
     • Geothermal
       • Positives : renewable, easy to harvest, continuous Negatives : area specific and expensive Steam made from heating of water from earth heat turns a turbine
     • Tidal
       • Positives : renewable, widely available Negatives : inefficient, non-continuous, high maintainence
     • Solar
       • Positives : renewable, widely available Negatives : not efficient or space effective, cost of solar cells high
   • Non-Renewable
     • Will Run out eventually - Fossil Fuels and Nuclear energy
     • Nuclear
       • Positives - high energy density, low maintainence Negatives - Radioactive waste, non-renewable, social stigma, cost and safety
     • Fossil Fuels
       • Positives : energy efficient and dense, works with current technology, easy to harvest Negatives : non-renewable, pollution, maintanance

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