SAASTE Technology/Activities/Electronic Circuits

Electrical System

Grade 9

Electronics
You will need the following component / Parts

Resistors (all ¼ Watt 5% carbon)
 * R1 - 680 Ohm
 * R2 - 4,7 K Ohm
 * R3 - 2,7 M Ohm (for activity 4)

Semiconductor
 * Q1 - BC337 (or equivalent)
 * LED 1- 5mm
 * LED 2 - 5mm infra red detector
 * LED (for activity 4)

A Resistor Colour Code Chart is available on the last page of this document.

Connect / build the circuit shown in the diagram below:

Note: The fly lead is simply a short length (approx. 10cm) of conductive wire (with both ends stripped of insulation)

Activity 1:
Attach the loose end of the fly lead to the negative (-) side of the battery and observe the output.

Now remove the fly lead and attach to the positive (+) side of the output and observe the output.

Activity 2:
Disconnect the fly lead from the battery. Touch the end of the fly lead with your bare fingers.

What do you observe?

Activity 3:
Connect another fly lead as shown in the circuit diagram below:



Insert both fly leads into a beaker containing water and observe the output.

Activity 4:
Use your original circuit and extend it by connecting LED 2 and R3 as shown in the circuit diagram below:

LED 2 - 5mm. infra red detector LED R 3 - 2,7 MΩ

Use any remote control (from a TV, Hi-Fi etc.). Bring it close to LED 2. Press any button on the remote control and observe the output.

Note: An LED is a transducer: it converts energy from one form to another

Component data:
 * R1 - Blue, grey, brown, gold
 * R2 - Yellow, violet, red, gold
 * R3 - Red, violet, green, gold

Note: 5%(gold), 10%(silver) or 20%(no 4th band) resistors may be used

The colours for the 4, 7 KΩ resistor was worked out like this: Each number of the value of the resistor correspond to the three bands on the one end of the resistor.

4 in the first band = yellow 7 in the second band = violet K in the third band would be orange. Because there is a decimal place (comma) between the 4 & 7, we move one decimal place and now have 2 zeros which correspond to red.

Try working out the colours for the following resistors: 47 KΩ, 50Ω, 330Ω, 100Ω , 560Ω , 390Ω.

Semiconductors:

Transistor Q1:                            BC 337:

B-Base; C-Collector; E-Emitter

Glossary
Resistor: An electronic component which slows or reduces the current and/or creates a voltage drop

L.E.D. (Light Emitting Diode): A special diode which emits light when a current flows through it.

Transistor: An electronic component which may be used as a switch or as an amplifier. They are broadly divided into PNP and NPN (the BC 337 used above is an NPN transistor)

Infra-red: A narrow band of the light spectrum invisible to the naked eye.

Anode: Positive

Cathode: Negative

Author: Ricardo Miller

Contributions by Osman Sadeck

Editor: Osman Sadeck