Embedded Files
basic principles
– potential difference
– current
– simple circuits and components
What is potential difference?
Potential difference is the difference in the amount of energy that charge carriers have between two points in a circuit. Potential difference is measured in volts (V) and is also called voltage.
An electric current (I) is a stream of charged particles, such as electrons, moving through an electrical conductor. Current is the rate at which electrons flow past a point in a complete electrical circuit. At its most basic, current = flow. An ampere, or amp, is the international unit used for measuring current.
An electron traveling through the wires and loads of the external circuit encounters resistance. Resistance (R) is the hindrance to the flow of charge.
How do you find the potential difference?
Multiply the amount of the current by the amount of resistance in the circuit. The result of the multiplication will be the potential difference, measured in volts.
This formula is known as Ohm's Law, V = IR
Watch this video and copy the calculation question examples.
Material Resistivity (ohm•meter) for common metals.
Silver 1.59 x 10-8
Copper 1.7 x 10-8
Gold 2.2 x 10-8
Aluminum 2.8 x 10-8
Iron 10 x 10-8
Why are most electrical cables made from copper and not silver?
Why would gold be used?
What is a Series Circuit?
A circuit is said to be connected in series when the same current flows through all the components in the circuit. In such circuits, the current has only one path. Christmas tree string lights are an example of a series circuit. This is nothing but a series of multiple tiny bulbs connected in series. If one bulb fuses, all the bulbs in series do not light up.
What is a Parallel Circuit?
A circuit is said to be parallel when the electric current has multiple paths to flow through. The components that are a part of the parallel circuits will have a constant voltage across all ends.
How does the resistance increase when the length of the conductor increases?
When you have longer length of wire, the current has to travel more distance, more the distance higher the number of obstacles it faces through its path. Therefore resistance increases with the length.
Why does it decrease if the cross sectional area increases?
When cross sectional area increases the space of the elctrons to travel increases(simply explained). Therefore less amount of obstacles for the current. Therefore when area increases the resistance decreases.
Questions: Show all working out!
What is the resistance of a silver wire if the resistivity is 1.59 x 10-8, the length is 1.5m and the diameter is 12mm. A:2.1 x 10-4
What is the resistance of a copper wire if the resistivity is 1.7 x 10-8, the length is 2m and the diameter is 6mm. A:1.2 x 10-3
Research Task
For each of the components shown give a brief description of its purpose and draw the symbol as it would be shown on a circuit diagram.
Electrical Safety
What is meant by double insulated?
Products manufactured with non-metallic cases are called double-insulated. If approved, they do not require grounding under the National Electrical Code. Although this design method reduces the risk of grounding deficiencies, a shock hazard can still exist.
Typical examples are blenders, coffee makers, blow dryers, drills, and other power tools. Appliances and tools of this type are called “double insulated”. They have two levels of insulating materials between the electrical parts of the appliance and any parts on the outside that you touch.
Safety Switches
About 40 per cent of the 4,500 house fires in NSW each year are caused by electrical faults and appliances. These fires could have been prevented by a licensed electrician checking the electrical wiring and installing safety switches.
Safety switches turn off the power immediately if an electrical fault is detected – preventing the risk of electric shock, death and fire.
To be fully protected, you need to:
have safety switches installed on all your circuits by a licensed electrician
do a quick and simple test at least every six months to ensure your safety switches are working properly.
House Safety switch
Why the three prongs?
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