Unit 1: Electricity

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  • Unit 1: Electricity
    • Current, Amps (I)=Q/T
      • Current is rate of flow of charge
        • Measured using an Ammeter in series
    • Potential Difference, Volts  (V)= W/Q
      • Measured using a Voltmeter in Parallel
      • Work Done (Joules) per unit charge (Coulomb) to move charge through a resistor.
    • Resistance,Ohms          (R) =V/I
      • Resistance is a measure of difficulty in the flow of current in a circuit or component
      • Ohms Law: As long as temperature is constant; the current through a Ohmic conductor is directly proportional to the potential difference across it
      • I/V Charactistics; On a graph a curve shows R is changing and not constant. If the gradient is SHALLOWER then the RESISTANCE IS HIGHER
        • Metallic Conductors (Most) are Ohmic therefore have a straight graph
        • Filament Lamp has a curve, the metal wire heats up causing more resistance
        • Semiconductors; are used in sensors
          • Thermistors; different types. Such as (NTC) Negative Temperature Coefficient
          • Light Dependent Resistors
          • More energy releases, more charge carriers
    • Resistivity (?) ?m= (R*A)/L [Resistance x Surface Area (M^2)]/Current
      • Superconductors have little/no resistance. This can be forced by cooling a material below its transition temperature
        • Can make strong electromagnets that don't need constant power source
    • Power, Watts (P)=IV
      • Resistance,Ohms          (R) =V/I
        • Resistance is a measure of difficulty in the flow of current in a circuit or component
        • Ohms Law: As long as temperature is constant; the current through a Ohmic conductor is directly proportional to the potential difference across it
        • I/V Charactistics; On a graph a curve shows R is changing and not constant. If the gradient is SHALLOWER then the RESISTANCE IS HIGHER
          • Metallic Conductors (Most) are Ohmic therefore have a straight graph
          • Filament Lamp has a curve, the metal wire heats up causing more resistance
          • Semiconductors; are used in sensors
            • Thermistors; different types. Such as (NTC) Negative Temperature Coefficient
            • Light Dependent Resistors
            • More energy releases, more charge carriers
      • By combining Power and Resistance you can say that:
        • P=I^2*R
        • P=V^2/R
      • 1 Watt =1 Joule / Second
        • Energy, Joules (J)= P x t
          • E=V*I*t
          • E=(V^2/R)*t
          • E=I^2*R*t
    • Energy, Joules (J)= P x t
      • E=V*I*t
      • E=(V^2/R)*t
      • E=I^2*R*t
    • EMF and Internal R
      • ?= V+v
      • ?=IR+ir
      • V = ? - v
      • V= ? - Ir
      • Low IR is great for batteries as less energy is lost. For safety high voltage power supplies have high IR so a short allows only a small current to flow
      • Terminal PD is the EMF - lost volts
        • V = ? - v

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