Physics

• Current


  The rate of flow of charge, Conventional current flow is in the direction of movement of positive charges
• Unit of current


  Ampere (A)
• Discovering current


  1. Current was discovered before the electron

  2. Conventional current is taken to be the flow of positive charges in a circuit
• Cell


  Current flows from the positive side of the cell to the negative side
• Ammeter


  • Measures current
  • Placed in series in a circuit
  • Current should enter the positive terminal
• If the ammeter is connected the wrong way round it will show a minus reading, but you can ignore this
• Resistance simulator model


  Demonstrates how current is represented and what causes resistance in a circuit
• Rope loop model


  Demonstrates how current is represented as a moving rope and what causes resistance as friction
• Making circuits to explain current flow


  1. Circuit 1: Brightness normal, Current 1A

  2. Circuit 2: Brightness very big, Current increased

  3. Circuit 3: Brightness medium, Current slower

  4. Circuit 4: Brightness almost down, Current faster
• Potential difference


  The energy given to each coulomb of charge as it passes through a cell
• Unit of potential difference


  Volts (V)
• Predicting and measuring potential difference


  1. Measure potential difference across a single cell

  2. Measure potential difference across a power supply

  3. Measure potential difference across a power supply with a resistor
• The cell provides the energy and makes the charges move
• The same number of charges go past each second all round the circuit
• The moving charges are already in the wire. They carry energy
• Charges return to the cell to collect more energy
• The bulb lights as soon as the charges start to move (they don't have to arrive from the cell)
• Charges deliver energy to the bulb where it is transferred to heat and light
• Current in amperes


  The amount of charge going past each second
• Bread and Lorries Electric Circuit


  Analogy to explain electric circuit concepts
• If the bakery manager speeds up the lorries


  The rate at which bread arrives increases
• If more bread is loaded into each lorry


  The rate at which bread arrives increases
• In a parallel circuit, the potential differences across the branches are all equal to that across the power supply
• Short circuit


  An "easy path", a bypass in a circuit
• A short circuit can be made when bare wires with a potential difference between them touch
• If points A and B are connected in the circuit


  Current will take the path across the conductor
• The potential difference across each lamp in the circuit is 5V
• If the potential difference across the lamps is reduced to 0V


  The lamps will become brighter
• Unit of resistance


  Ohms (Ω)
• Resistance


  Tells us how much potential difference (V) is required to make 1 A of current flow
• Increasing the potential difference across a resistor


  Increases the current that flows through it
• Symbol for variable resistor

  Arrow through the symbol for the power supply indicates a variable power supply
• Experiment to investigate resistance


  1. Independent variable: voltage

  2. Dependent variable: Current

  3. Controlled variable(s): Resistor
• A voltmeter is included in the circuit to give an accurate reading and create resistance
• The graph of current vs potential difference has a positive incline
• Infrared radiation


  Part of the electromagnetic spectrum, a family of waves that travel through space at 300 million metres per second carrying energy
• Other types of electromagnetic radiation

  • Absorb
  • Emit
  • Transmit
  • Reflect
  • Scatter
• Absorb


  • The energy is taken into the surface
• Emit


  • Energy given out
• Transmit


  • Allow to pass through