SNC 1D Date: ______
Current Electricity – circuits, current, measuring current
What is it?
è Electricity in motion
è Electrons flowing from one place to another
è More useful than static electricity
è Measured using an ammeter
· Electric current is able to flow through a conductor, like copper.
· An insulator does not let electrons flow (wood, air)
Electric Circuits
· For electricity to flow there must be a closed circuit.
· This means there must be a complete path for the electrons to travel.
· If there is a break in the circuit, it is called an open circuit. It will not allow electrons to flow.
· An electrical circuit must have an energy source, such as a battery or a power supply that pushes the electrons around the circuit.
· A 1.5 V dry cell that you would use at home is an example of a device that supplies 1.5 volts of force to push electrons around the circuit. A 12 volt car battery is very similar, it uses six 2 V cells connected together to produce 12 volts of force.
· A complete circuit has a power supply and some device that uses power, called a load, connected in a circle.
· Lamps, toasters and radios are examples of loads.
· A controlled circuit has a switch, which is used to open or close a circuit.
· A fused circuit has a fuse, a safety device that stops too much electricity from flowing.
· A short circuit has a path that lets electrons flow, but it has no load. It is very dangerous.
· Electrons in a circuit flow out of the negative terminal and back to the positive terminal.
· This flow of electrons is called current.
· A simplified drawing of a circuit uses symbols to represent the various parts of the circuit. These are called circuit diagrams. (see your chart for symbols)
Draw circuit diagrams for the circuits pictured above in this note:
Measuring Current:
Just like the flow rate of water passing through a hose can be calculated by dividing the amount of water passing a point by the time,
flow rate = amount of water passing (9 L) / time (3 min) = 3 L / min.
the flow rate of electrons passing through a wire can be calculated by dividing the amount of charge by the time
current (I) = charge passing a point (Q) / time (s)
= 9 coulombs / 3 seconds
= 3 amperes
§ The unit of measure for current is the Ampere (A)
§ The symbol for current is I
§ Current is the amount of charge (or amount of electrons) that pass through a wire per unit of time (second)
Ammeter
· measures the amount of current flowing past a single point in a circuit
· it is connected in series
Potential Difference (Voltage):
§ Electrons flow through a conductor when there is a surplus of electrons at one pole and a deficit at the other pole. The electrical potential of the two poles is different.
§ Although the electrons have the potential for doing work, they cannot do so until the cell is connected to a load and the circuit is closed.
§ Potential Difference (V) – the loss in energy caused by electrical resistance when electrons flow through a conductor.
§ It is measured with a voltmeter. The units are volts (V)
§ The power supply increases the energy
§ The load decreases the energy
Voltmeter
· measures the drop in electrical energy or “pressure” between two points in a circuit
· always connected in parallel because it must read the difference between 2 points in the circuit
TVO videos:
Electricity: Current http://www.youtube.com/watch?v=5laTkjINHrg
Electricity: Potential Difference http://www.youtube.com/watch?v=F1p3fgbDnkY
Electricity: Resistance http://www.youtube.com/watch?v=YGvu9iqjJq4
To Do:
complete “Measuring Current Lab”
complete “Potential Difference Lab”
complete circuit diagram worksheets
Read text p.324-335