P4

• Define current

  The rate of flow of charge
• Define potential difference

  The energy per unit charge
• Define resistance

  A components ability to withstand current
• Name the symbol

  Cell

  
• Name the symbol

  Resistor

  
• Name the symbol

  Battery

  
• Name the symbol

  Variable resistor

  
• Name the symbol

  Open switch

  
• Name the symbol

  Closed switch

  
• Name the symbol

  Ammeter

  
• Name the symbol

  Voltmeter

  
• Name the symbol

  Bulb

  
• Name the symbol

  diode

  
• Name the symbol

  Fuse

  
• Name the symbol

  LDR

  
• Name the symbol

  LED

  
• Name the symbol

  Thermistor

  
• What is a series circuit?

  A circuit containing a single pathway for current to flow - once one component is broken, all will stop working
• Series circuit rules

  P.D = The total PD of the cells is shared between components

  Current = Remains the same along the whole pathway

  Resistance = Resistance of components will sum to total resistance of circuit
• What is a parallel circuit?

  A circuit containing more than one pathway for current to flow - if one pathway is broken the others remain working
• Parallel circuit rules

  P.D = Remains the same for each pathway

  Current = Total current leaving the battery is shared between various pathways

  Resistance = Total resistance of the circuit is less than that of the smallest resistor
• Units and symbols

  Current, I - Amps (A)

  Potential difference, V -Volts (V)

  Resistance, R - Ohms (Ω)

  Charge, Q - Coulombs (C)

  Energy, E - Joules (J)

  Power, P - Watts (W)

  Time, t - Seconds (s)
• Conversions

  1kW = 1,000W

  1MW = 1,000,000W

  1mA = 0.001A
• What is an LDR?

  Light Dependent Resistor - as the brightness increases the resistance decreases
• What is a thermistor?

  A type of resistor that changes depending on temperature. Ad the temperature increases the resistance decreases
• RP - Resistance of a wire = variables

  Independent variable = Length of wire

  Dependent variable = Resistance

  Control variables = Type of metal and diameter of wire

  Conclusion = As length of wire increases, the resistance also increases
• RP -Resistance of a wire

  1. Attach crocodile clip at 0cm on the wire
  2. Attach second crocodile clip 10cm away
  3. Close switch and record current with ammeter and the PD across the wire with a voltmeter
  4. Turn off the power pack and move the second crocodile clip another 10 cm away
  5. Close switch again and record current and PD at new length
  6. Repeat for different lengths
  7. Calculate resistance using equation
• RP - Resistance in series and parallel circuits = variables

  Independent variable = Circuit type

  Dependent variable = Resistance

  Control variables = Number of resistors and power source

  Conclusion = Adding resistors in series increases the total resistance of the circuit. Adding resistors in parallel decreases the total resistance of a circuit
• RP -Resistance in series circuits

  1. Build a circuit with a battery, resistor and ammeter - note the PD of the battery
  2. Measure the current through the circuit with the ammeter
  3. Add an identical resistor to the circuit
  4. Measure current and again calculate the resistance
  5. Repeat until all 4 identical resistors have been added
  6. Plot graph of results
• RP - Resistance in parallel circuits

  1. Use same equipment as series circuit so test is fair and build the same initial circuit
  2. Measure current and calculate resistance
  3. Add an identical resistor in parallel
  4. Measure current now and calculate resistance again
  5. Repeat until all resistors used
  6. Plot graph
• RP = I-V relationships in circuits = Variables

  Independent variable = Current

  Dependent variable = Potential difference

  Control variables = Number of components and power source
• RP = I-V relationships in circuits

  1. Set up circuit with battery, ammeter, variable resistor and a component with a voltmeter attached in parallel around the component
  2. Vary the variable resistor - this alters the current in the circuit and the PD across the component
  3. Take readings from ammeter and voltmeter to see how PD across components varies as current changes
  4. Repeat each reading 3 times to get average PD of component at each current
  5. Plot graph for each component
• I-V characteristics for Ohmic conductor results

  Current is directly proportional to PD

  
• I-V characteristics for filament lamp

  As current increases, temperature increases so resistance increases, meaning less current can flow so graph gets shallower (curves)

  
• I-V characteristics for diode

  Current will only flow through a diode in one direction as it has very high resistance in the other direction