Labs from Chicago, Winter 1994 :
Circuit Diagrams and Components.

Dr. Rich Kron, Dr. Heidi Newberg, and Luisa Rebull
Labs written for the CARA Space Explorers, Winter 1994

This is meant to be handed out to the students.

I. Introduction

In this lab we will learn to assemble electrical circuits. To work, all circuits need a source of electricity. For our circuits, we will use a battery for that source of electricity. The electricity from the battery is used to power various circuit components, like light bulbs, electric motors, light-emitting diodes (LEDs), or buzzers. Switches are used to control which parts of the circuit the electricity goes through. Fuses are used when we want to protect a component from getting too much electricity by mistake. Fuses are used mainly to protect people from faulty or misused circuits, or to protect expensive components from getting destroyed.

Instead of drawing what the components actually look like, engineers use symbols to represent the components in a circuit diagram. The circuit diagram is then used (often by an electrical technician) to assemble the circuit. Here are the symbols for some common circuit components. Don't worry about what all of these things are; we will introduce their functions as we go along. Keep this sheet handy in future weeks so that you can figure out what the symbols mean.

(none of the graphics preserved; we cut and pasted them from a xerox...) We had symbols for:

resistor: variable resistor: photo resistor: thermistor: non-polarized capacitor: electrolytic capacitor: variable capacitor: inductor: iron-core inductor: adjustable inductor: conductors not joined: conductors joined: single pull, single throw switch (SPST): single pull, double throw switch (SPDT): double pull, double throw switch (DPDT): multipoint switch: diode/rectifier: light-emitting diode (LED): zener diode: antenna: fuse: quartz crystal: hand key: motor: buzzer: npn transistor: triode vacuum tube: incandescent lamp: single cell battery: multi-cell battery: chassis ground: earth ground: ammeter: voltmeter:

Using these components, we can assemble many circuits. For instance, we could make a circuit to light a light bulb with a battery [see below for picture]. We draw a 1.5 volt, single cell battery, and an incandescent lamp. Then we draw a line, which represents a wire, from one lead (pronounced 'leed') of the incandescent lamp to the battery. Finally, we draw a line from the other lead of the incandescent lamp to the other side of the battery. It doesn't matter where the lines are drawn or what shape they are drawn in, but to make the diagrams neat and easy to read, we usually draw only horizontal or vertical lines. When we build the circuits, we do not need to have the same wire shapes to make the circuit work, we just need to make sure that electricity can flow from the battery to the lamp and back to the battery.

II. The Experiment

This laboratory consists of building five circuits. In each case, you will be given a circuit diagram from which to construct the circuit. Check the list of symbols at the beginning of the lab to figure out what circuit components to use.

A. Light bulb, motor, buzzer, and LED

Build each of the circuits pictured here, using the 1.5 volt battery. For each circuit, attach the component in one direction, and then turn it around so that the electricity flows the other direction through the component.

Which components work in both directions?

Which components only work in one direction?

B. Switch

When you build a circuit with a switch, it is a good idea to assemble the circuit with the switch open. After the circuit is finished, then the switch can be opened and closed. A circuit in which there is no way for the electricity to travel from the positive terminal of a battery to the negative terminal of the battery is called an open circuit.

C. Fuse

Notice that in this circuit you are using a 3 volt battery. You can make a 3 volt battery by putting two 1.5 volt batteries together. That is why a 1.5 volt battery is called a single cell battery and bigger batteries are usually multi-cell batteries. They are usually made from putting two or more 1.5 volt batteries together. Batteries usually come in 1.5, 3, 4.5, 6, 9, or 12 volts.

First, put the circuit together as shown in the figure. When you close the switch, the light should light. Then, disconnect the wire from one side of the light bulb and touch it to the lead on the other side of the light bulb while looking at the fuse. You should see the fuse "blowing." Now reconnect the wire on the other side of the light bulb. Does the light go on as it did before? If not, why not?

Why do you think there is a fuse in this circuit?

D. Resistor

This circuit uses a switch called a single pull, double throw switch. It can make the circuit open or closed, but it can also change which part of the circuit the electric current flows through. When the switch is in position 1, the current goes directly from the battery through the light bulb. When it is in position 2, the current goes through a resistor before going through the light bulb.

Is there any difference when the current goes through the resistor? If so, what is the difference?

E. Railroad crossing

Make sure you get the diodes in this circuit in the right direction! The side with the bigger lead is the negative side (you may have to hold the diode up to the light to see which side is the bigger side).

It looks sort of like this:

	------------   -----
	|  		\  \   |
this is the		 \  \  | this is the 
negative side!	  \  \ | positive side!
	---------------   --

Important Disclaimers and Caveats


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