Topic 3.3: Key Concepts Chemical Energy separates electrical charges in cells. Charges can flow through conductors, but not insulators. Moving electrical charges form an electric current. A load resists the flow of current. Conductors must form a closed loop to allow current to flow.

Concept 2: Charges Can Flow Through Conductors, but Not Insulators When 2 different solid materials are rubbed together, electrons can be transferred from one material to the other. The electrons will either on the surface of the new material or Any material that electrical charges can move through is called a How easily charges move through a material is called A material through which charges cannot travel is an stay Electrons can move through pretty much all metals, but some metals are better conductors than others travel through it conductor conductivity insulator

Discussion Questions Explain why electrical wires are covered by an insulator.

Concept 3: Moving Electrical Charges Form An Electrical Current from a source causes charges to move through the , carrying energy to the device The moving charges are called an Symbol for current: Current is measured in : Chemical Energy conductor electric current I amperes A

Concept 3: Moving Electrical Charges Form An Electrical Current For example, the equation I = 3 A means that the current (I), is three amperes (3 A) A smaller unit of electric current is the milliampere (1A = 1000 mA) Discussion Question: Describe the relationship between moving charges and electric current.

Concept 4: A Load Resists The Flow of Current - a device that converts electrical energy into another form of energy E.g. A light bulb is a load that transforms electrical energy into light energy As pass through a load, they energy as electrical energy is converted to another type of energy Load E.g. a radio is a load that transforms electrical energy into sound energy electrons Figure 3.18: A light bulb is a load because it converts electrical energy into heat and light energy. lose

A Load Resists The Flow of Current A load the flow of Electrons in the current with atoms that make up the load, or with each other The interfere with the flow of current How much the flow of current in hindered is known as (symbol: ) unit of measurement is resists current collide E.g. a radio is a load that transforms electrical energy into sound energy In general, metals have less resistance than non-metals, hence why they are better conductors. collisions resistance R Ω (Ohm)

Factors Affecting Electron Flow - the longer the wire, the the resistance because there is a higher chance that the electrons will collide with other ions and electrons along the way. Length of conductor higher

Factors Affecting Electron Flow - the thicker the wire, the the resistance because there are many more atoms, and more free electrons in the wire to carry the current Thin wires have resistance because there is for the electrons to move - the the temperature, the higher the resistance because increased movement of the atoms and ions creates more collisions with the moving electrons Diameter lower less space higher Temperature higher

Example of Resistance: Filament in a Light Bulb Charges move from a large wire (electrical cord) into a thin wire (filament) Since charges have less room in the filament (the filament the movement of charges), they collide with atoms so hard that the filament gets very hot The heat makes the filament glow (“light up”) resists Load has resistance – Video: https://www.connectschool.ca/mod/mheresource/view.php?id=757772

Discussion Questions Use the source, current, and load to describe how you think a flashlight works

Concept 5: Conductors Must Form a Closed Loop to Allow Current to Flow - made up of a , , and a connected in a way that allows current to flow For current to flow, the circuit must form a Example: Source = Load = Conductor = Electrical circuit source load conductor closed loop Electrochemical cell lightbulb Wires

Short Circuits Short Circuit – a circuit with a that is , making the current so that it is dangerous Example: if there was not a load (light bulb) to resist the flow of current, the current would be so large that the conductor would get very hot and start a fire! resistance too high low

Modelling the Flow of Current (Part A) Negative terminal repels the negative charges already in the conductor Positive terminal attracts the charges already in the conductor Electrons move along the wires and electrons from the cell move into the conductor The conductors already have electrons in them negative

Modelling the Flow of Current (Part B) As the electrons pass through the , they transfer some of their energy to the load The electrons then leave the load and return to the electrochemical cell load The conductors already have electrons in them

Modelling the Flow of Current (Part C) Electrons enter the cell and combine with positive ions to become Over time, there are fewer electrons at the negative terminal and fewer positive ions at the positive terminal The worker can carry more electrons up the ladder, keeping the number of separated charges neutral The conductors already have electrons in them equal at all times

Controlling the Flow of Current In a typical circuit, a controls in a circuit Example: switch is , meaning the circuit is , current from flowing Switch is , meaning the circuit is , allowing current to flow through and the light turns on switch current open open stopping closed closed Figure 3.20: How a switch controls current in a circuit

Using Circuit Diagrams Draw a circuit diagram from the previous slide’s image.

Example of a Circuit Diagram Draw the circuit for the following image: Draw a circuit diagram from the previous slide’s image.

Comparing Water & Electrical Circuits Water circuit – a lifts the water to a higher level against the pull of Electrical circuit – cell or battery is like the pump pump A valve at the top of the pipe controls where the water flows down. When the water runs down, it turns a water wheel Electrical circuit – it raises charges to a higher level of electrical potential energy The switch is like the valve. It determines whether the electrons are allowed to flow through the circuit. When the electrons are allowed to flow, the current runs through the load and lights the light bulb gravity

Discussion Questions Explain what “short circuit” means. Describe the role of a switch in an electrical circuit