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P4 Electric Circuits (Current and Charge (electric current is the rate of…

- - - - Current = Charge ÷ Time
      - (coulombs, C) (amperes, A) (s)
    - - the no. of electrons that pass through that point per second will be same
  - - - in reality, electrons flow from -ve to +ve in an electric circuit
- - - - a resistor at constant temperature
        
        current is directly proportional to potential difference across the resistor
        
        resistance (V ÷ I) is constant
        
        regardless of direction of p.d. and current
        
        straight line
        
        passes though origin
        
        greater resistance = shallower gradient
      - Fixed Resistor
        
        limits current in a circuit
    - - current is not directly proportional to potential difference
        
        resistance of bulb increases as current increases
        
        resistance of filament increases as temperature increases
        
        resistance is same for same current size regardless of direction
        
        metal atoms vibrate more, resisting passage of electrons
        
        gradient decreases as resistance increases
        
        non-ohmic conductor
    - - in forward (one-way) direction, current is not proportional to p.d.
        
        resistance curves towards y-axis
        
        resistance changes as current changes
        
        non-ohmic conductor
      - in reverse direction, current is virtually 0
        
        diode have very high resistance
    - - temperature-dependent resistor
        
        resistance decreases as temperature increases
        
        used in sensor circuits
    - - light-dependent resistor
        
        resistance decreases as light intensity increases
        
        used in sensor circuits
  - - - allows current to be varied
        
        a cell & variable resistor = powerpack
      - contains a long piece of wire in a coil
        
        slider can be used to adjust length of wire
    - - Zero Error
        
        a reading on a measuring instrument when the value should be zero
        
        Systematic Error
        
        error cannot be reduced by carrying out repeats
        
        subtract the zero error from all the readings
        
        a small resistance is seen when the length of wire is 0
        
        crocodile clip is not exactly at zero
        
        some resistance caused by contact between clip and wire
      - Heating Effects
        
        if temperature increases, resistance will also increase
        
        use low p.d. to keep current low to reduce wires heating
        
        turn off the current between taking readings
- - - - materials become charged by friction
        
        material that lose electrons >> positive charge
        
        material that gains electrons >> negative charge
    - - electrons gained by rods
    - - electrons gained by cloth
  - - - Like charges repel.
        
        Unlike charges attract.
      - non-contact force acts at a distance
        
        the greater the distance, the weaker the force
    - - arrows showing where a small positive charge will move in relation to object
    - - a charge is induced on the object's surface when the charged object come near
- - - - (volts, V) (joules, J) (coulombs, C)
      - Potential Difference = Energy Transferred ÷ Charge
- - - - current though each component is the same
    - - the bigger the component's resistance, the bigger its share of p.d.
    - - Rtotal = R1 + R2
      - adding more resistors in series increases total resistance
- - - - charge flows separately to each component
        
        if one circuit branch breaks, charge still flows in other parts
        
        potential difference across each component is the same
        
        current is shared through separate branches
        
        total current = sum of currents through separate branches
        
        the bigger the resistance of the component, the smaller the current through it
        
        total resistance < the resistance of the lowest resistor in circuit
        
        adding more resistors in parallel decreases the total resistance
        
        1/R = 1/R1 + 1/R2