ONACD - Editable curriculum designed for teachers by teachers

Simple Circuits

Symbols and Devices

ONACD –Editable Curriculum designed for teachers by teachers

A vacuum salesman appeared at the door of an old lady's cottage and, without allowing the woman to speak, rushed into the living room and threw a large bag of dirt all over her clean carpet. He said, "If this new vacuum doesn't pick up every bit of dirt then I'll eat all the dirt."

The woman, who by this time was losing her patience, said, "Sir, if I had enough money to buy that thing, I would have paid my electricity bill before they cut it off. Now, what would you prefer, a spoon or a knife and fork?"

ONACD - Editable curriculum designed for teachers by teachers

Now the fun begins SymbolsTo be able to communicate how a circuit is connected it is

much more effective to symbols. Simple circuits are made with some or all of the following components:

Note: Often resistors are drawn instead of light bulbs since they are essentially the same thing.

Component Symbol AlternateCell (1.5V)

Battery (9V)

Wire

Resistor

Lamp Light Indicator

Switch Pole Push

ONACD - Editable curriculum designed for teachers by teachers

More funSince we can calculate resistance (R) we only need to be able to

measure voltage (V) and current (I). To measure voltage we use a Voltmeter. To measure current we use an Ammeter.

Aside: A meter is a device for measuring. A metre is a unit of length.So a “metre meter” is a stick that measures the unit length of distance.

Component SymbolVoltmeter

Ammeter

ONACD - Editable curriculum designed for teachers by teachers

Consider the following simple circuit with a 1.5 V dry cell and a light bulb (or resistor).

How should an Ammeter be connected to measure current going into the resistor?

In order to measure current the device has to actually be part of the circuit. Think back to the analogy of water flow. The current is based on flowing charge.

Note: it doesn’t matter where in the circuit as the current will be the same.

ONACD - Editable curriculum designed for teachers by teachers

How should a Voltmeter be connected to measure voltage across the resistor?

In order to measure the voltage the device compares the difference between two points on the circuit. So the voltmeter connects at each end of the resistor to measure the amount of electric attraction from one end of the resistor to the other.