Electric Circuits

• To model electric circuits consisting of a power supply, load and conducting path

• To understand the difference between cells and batteries

• To draw and construct appropriate circuit diagrams using the correct symbols

• To define current and voltage within the context of electrical circuits

• Conductors & Insulators

  Electrical conductors are materials which allow electricity to flow easily.

  • Most metals are good conductors due to the “sea” of delocalised electrons present in metallic bonding.

  • Liquids with dissolved ions can conduct electricity too (but not as well).

  • Conductors & Insulators

    Electrical insulators are materials which resist the flow of electricity (prevent it from flowing easily).

    • Most non-metals are good insulators (i.e. poor conductors) due to the lack of delocalised electrons. Their electrons are tightly bound to their nuclei.

    • liquids with no ions, like pure water, or oil, won’t conduct electricity.

    • An electric circuit is a pathway, usually made of metal wires, that conducts electricity.In a basic circuit, electrons are continuously moving away from the negative electrode of a power source, and towards the positive electrode.

• An electric circuit is a pathway, usually made of metal wires, that conducts electricity.

  
  

  Circuits consist of three essential components:

  • a power supply to provide the electrical energy

  • a load (or loads) in which electrical energy is converted into other useful forms of energy (e.g. light, heat, sound)

  • a conducting path (wires) that allows electric charge to flow around the circuit.

• Circuit Diagrams

• Maps of electric circuits need to be drawn so that people all over the world can read them. These maps are called circuit diagrams. 

  
  

  Circuit diagrams use straight lines for connecting leads and symbols for other parts of circuits.

• Cells are single electrochemical units that convert chemical energy into electrical energy.

  For example, a 9V battery often contains six 1.5V cells inside it.

Check-in:

Can you:

• Define the terms ‘conductor’ and ‘insulator’?

• to identify which materials are conductors which are insulators, and why?
  
  

• Explain how different materials are able to conduct electricity based on their chemical structure?

Electric charge (Q) is a fundamental property of matter, like electrons (negative and protons (positive).

  Units: Coulombs (C)

Electric current (I) is the rate of “flow” of electric charge through a conductor over time. 

  Units: Amperes (A) = Coulombs per second (C/s)

Reminder: Electrons don’t move all the way around a circuit; they vibrate in place and the energy moves instead!

• When scientists first characterised how electrons move in a circuit, they thought electrons were positive particles.

• So they accidentally decided that current flowed in a circuit from the positive to the negative terminal of the power supply. 

  • So, conventional current is in the opposite direction to electron “flow”

  • Voltage or Potential Difference (V) is the difference in the electrical energy stored between two locations. 

      Units: Volts (V) = Joules per Coulomb (J/C)

    • Voltage is a potential energy since it only exists to transfer that energy to electrons in a circuit

    • Voltage can be created by things like chemical batteries, generators, solar panels and storm clouds

• In the same circuit, voltage and current are proportional

  • If the voltage increases by n times, current increases by n times

  • If the voltage decreases by n times, current decreases by n times

• This can be written mathematically as:

V∝ I

“Voltage is proportional to current”

• Recall that power (in Watts) is the amount of energy per unit time:

• In an electrical circuit, power (still in Watts) is voltage multiplied by current:

• Current is measured using an ammeter which is connected in series

• Voltage is measured using a voltmeter which is connected in parallel across the device that is being measured