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Physics, Dynamics, Practical electricity, General Wave Properties,…

- - - - Action and reaction forces act on different bodies
    - - Forces that act at point of contact between bodies
    - - Forces that act on bodies without contact
- - - - g on Earth is ~10m/s²
        g on Moon is 1/6 of Earth
  - - - Speed approaches a constant velocity
        (terminal velocity)
- - - - Short circuit: Live wire touches neutral wire
        Overloading: Too many appliances on one socket
      - The large amount of current generated can melt insulation and start an electric fire
- - - - High resistivity: Much electrical energy is converted to thermal energy
      - High temperature tolerance: Heating element will not melt
  - - - Tungsten: High melting point
      - Coiled: Increased length, more resistance, more light
      - Bulb filled with argon: Inert gases prevent oxidation of filament
- - - - Energy increases with amplitude
- - - - Example: Electromagnetic waves
  - - - Compression: Compressed region of particles
        Rarefaction: Stretched region of particles
- - - - Electromagnetism
        
        Magnetic effect of a current
        
        Straight wire
        
        Direction and amplitude of current changes magnetic field
        
        Higher amplitude, stronger field strength
        
        Direction follows Right Thumb Rule
        
        Magnetic field lines form concentric circles around wire
        
        Circles get closer together nearer to the wire
        
        Field strength stronger
        
        Solenoids
        
        Field lines are almost straight and parallel near the centre
        
        Direction of field follows Right-Hand Grip Rule
        
        Current is defined as conventional current
        
        Magnetic strength can be increased by:
        
        Larger current
        
        More coils
        
        Inserting soft magnetic core
        
        Field lines are closed loops along coil circumference
        
        Combined magnetic fields
        
        Two fields acting in same direction create stronger field
        Two fields acting in opposite directions create weaker field
        
        Unbalanced fields around wire in magnetic field produces a catapult force
        
        Direction can be found with Fleming's Left Hand Rule
        
        Forces between two wires
        
        Opposing directions currents repel
        Same directions currents attract
        
        Current carrying coil
        
        Catapult field generates pair of equal and opposite forces
        
        Force pair rotates coil
        
        DC motor
        
        Current flows from P and X to Y and Q
        
        Coil turns anticlockwise
        
        Y will touch P while X touches Q
        
        Direction of current reverses every half rotation, coil keeps turning
        
        Increasing turning effect
        
        Increasing turns of coil
        
        Increasing current
        
        Inserting soft iron core
        
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        Electromagnetic induction
        
        In a coil
        
        Current is induced when magnet moves in coil
        
        Current is induced by constant cutting of magnetic field lines, specifically due to relative motion
        
        Cutting of field lines also known as magnetic flux
        
        Galvanometer deflects in direction and with amplitude of current induced
        
        Current induced follows a direction that opposes the magnet's motion via Right-Hand Grip Rule
        
        Imagine the direction the current would take to produce an electromagnet repelling the magnet
        
        When Force+Field=Current
        
        In a wire
        
        Follows Fleming's Right-Hand Rule
        
        AC generators
        
        Current is induced when the coil rotates
        
        Current flows from A to B and C to D
        
        After turning, current flows from B to A and D to C
        
        Every half turn, the current reverses its direction, hence an alternating current
        
        Changing output
        
        Doubling turns in coil
        
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        Doubling rotation speed
        
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        Increasing EMF
        
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        Dynamo
        
        Magnet rotates, coil stationary
        
        Transformers
        
        Uses
        
        Transformers step up or down mains supply (240V) to required voltage for different appliacnces
        
        Reduced line loss along power cables with less current but same power
        
        Contains two coils of insulated wire wound around an iron core
        
        Coils known as primary and secondary coils
        
        Step up: Primary<Secondary Step down: Primary>Secondary
        
        AC current is induced in secondary when power is supplied to primary
        
        Primary coil induces magnetism in iron core, which induces emf in secondary coil
        
        Transformer only works with AC, as AC current induces magnetic flux that DC cannot
        
        Ratios of voltage and current equal the ratio of the number of coil turns
        
        Improving efficiency
        
        Effective soft magnetic core
        
        Low resistance wires
        
        Special core design ensuring that magnetic field is linked completely
        
        Primary coil is wound on top of secondary coil in a closed iron core
        
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        Laminated core reducing flow of eddy currents
        
        Current may be induced in the core itself, called eddy currents
        
        Cathode Ray Oscilloscope (CRO)
        
        Uses
        
        Measuring DC and AC voltages
        
        The larger the voltage, the greater the displacement
        
        Displaying waveforms
        
        Measuring time and frequency
    - - Stroke bar several times in same direction with same polarity
        
        End of bar always has opposite polarity to magnet used
    - - A strong magnet aligns the domains of a nearby magnetic material without direct contact
  - - - Unmagnetised means randomly aligned domains
      - Magnetisation aligns the domains in one direction
  - - - Process misaligns domains
    - - Place magnet in solenoid
        
        Close switch and remove magnet slowly
        
        Periodic changes in current misaligns the domains
- - - - Energy possessed by object in motion
      - KE = ½mv²
    - - Energy possessed by object due to relative position from the ground
      - GPE = mgh
    - - Mechanical energy = KE+GPE
      - Total mechanical energy of an object is constant (ignoring friction)
- - - - Atmospheric pressure pushes down on liquid in a dish, which pushes some liquid into a tube with a vacuum
        
        Mercury is most commonly used for its density
- - - - Smooth surface
        Reflected in one direction
        Clear distinct image
    - - Rough surface
        Reflected in different directions
        Unclear image
- - - - n also found by c/v, where c is the speed of light in a vacuum and v is the speed of light in the medium