Term 3

• Circuit diagrams


  Used to help show where components should go
• Components that make up an electrical circuit

  • Wires
  • Motor
  • Battery
• Common circuit symbols


  • LED – Light emitting Diode
  • LDR – Light dependent resistor
  • Buzzer
  • Heater
  • Motor
• Drawing a simple circuit diagram

  1. This circuit should have a switch, a motor, a variable resistor and 3 cells connected as a battery

  2. This circuit should have a switch, a light and a cell
• Your turn: Draw the following circuits

  1. A switch, 2 cells connected as a battery, an ammeter, a lightbulb

  2. A switch, 3 cells connected as a battery, a fuse, a motor and a switch

  3. A switch, an LED, a cell, a variable resistor

  4. A circuit to represent the components of a hairdryer
• Series circuit


  If a component breaks then the whole circuit will stop working
• Parallel circuit


  If a component breaks then everything on a different loop will continue to work
• Electricity


  The flow of electrical power or current, usually done via the movement of electrons
• Build a simple circuit


  Draw a simple circuit with a variable resistor, switch, LED and a cell
• Electricity


  The existence of electricity has been known for centuries because of Lightning, electric fish and static electricity but no one knew how to study it
• It was discovered that spinning a glass globe could produce a small electric charge

  1700s
• Luigi Galvani discovered that electricity could make muscles twitch in a frog leg. This inspired Mary Shelley to write the book Frankenstein


  Late 1700s
• Alessandro Volta created the first battery called the Voltaic Pile


  Late 1700s
• Once electricity generation was discovered research and inventions happened quickly
• Current


  The flow of negatively charged electrons
• Voltage


  The measure of the size of the 'push' that causes current to flow around a circuit
• Charge


  Electrical energy that is positive or negative
• Potential difference


  The difference in charge across a component
• Resistance


  Opposes the 'push' provided by the voltage in a circuit
• Current


  • The flow of electrons in a circuit
  • The unit for Current is Amperes (A) but may be represented in an equation with an I
  • A high current means that there are lots of electrons flowing through a circuit
  • When an battery is connected to a circuit all the electrons in the circuit will move in the same direction at the same time
  • There will always be the same amount of current in a circuit although it might be split between different branches of a parallel circuit
• Voltage


  • The measure of the 'push' force that causes current to flow
  • Voltage is measured in Volts and the unit is shown as V
  • Large batteries like 12V car batteries have more 'push' than a small D-cell battery, which is 1.5V
  • If you have multiple batteries joined together you add up the voltage for the total voltage in the circuit
• Ohm's law


  Relationship between voltage, current and resistance
• Units for Current, Voltage and Resistance


  • Ohms - Resistance
  • Volts - Voltage
  • Amps - Current
• Resistance in circuits


  • Can arise from many different things
  • Makes it harder for electrons to flow around the circuit
  • The less resistance, the more current can flow (similar to water in a pipe)
  • Caused by resistors, material of wires/components, or temperature of wires/components
• Georg Ohm


  • Realised voltage, current and resistance were linked
  • Created Ohm's Law equation
• Potential difference


  • Proper name for Voltage
  • Difference in voltage across a component
• Using Ohm's Law


  1. Calculate potential difference across a 5Ω resistor with 2A current

  2. Calculate resistance of a lamp with 3V potential difference and 0.5A current

  3. Calculate resistance of a wire with 6V potential difference and 0.1A current

  4. Calculate current with 230V potential difference and 10Ω resistor

  5. Calculate potential difference required for 2A current in 12Ω resistor

  6. Calculate current with 12V potential difference and 100Ω resistor