CIRCUIT COMPONENTS

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• D.C. and A.C. currents• Fuses• Plug• Voltmeters• Ammeters• Fixed resistors• Variable resistors• Thermistors (input transducer)• Light dependent resistors (input transducer)• Capacitor• Diode (rectifier)• Transistors

1. D.C and A.C.

• Current is the number of charge carries moving past a point per unit time in a conductor. (measured in amps A)

• There are two types of current:– D.C. – A.C.

i) D.C. stands for direct current.- this is current that moves in one direction.- it moves from positive to negative (conventional current)- a cell is an example of a source of D.C.

ii) A.C. stands for alternating current.- this is current that changes direction.- it does NOT move in one direction only.- a mains socket is an example of a source of A.C.

2. Resistors

A resistor works to reduce current flow. (measured in ohms Ω)

i) A fixed resistor is a resistor with only one value. The value of its resistance is shown by the color coding.

-The first band gives the first digit.-The second band gives the second digit.-The third band gives the multiplier.

(bb – roy – g – bv - gw)-The fourth band gives the tolerance.

Gold = +- 5%Silver = +- 10%No colour = +- 20%

Color Value

Black 0

Brown 1

Red 2

Orange 3

Yellow 4

Green 5

Blue 6

Violet 7

Grey 8

White 9

First band - yellow = 4Second band - violet = 7Third band - red = 2Fourth band - gold = +-5%

Therefore, the value of the resistor is:47 x 102Ω = 4700Ω with tolerance of +-5%

First band Second band Third band Fourth band Resistance

Brown Red Blue Silver

Black Yellow Brown Gold

Blue Yellow Black No color

Black White Black Silver

32000Ω +- 10%

Complete the table below

ii) A variable resistor is a resistor whose resistance can be adjusted. It is also called a rheostat or potentiometer.

3. Fuses• A fuse is a type of low resistance resistor that

acts as a sacrificial device to provide overcurrent protection.

• When there is too much current, the fuse blows-up.

• In larger circuits, circuit breakers are used. They act as fuses.

4. Voltmeter

• A voltmeter is an instrument used to measure potential difference between two points in a circuit.

• It is connected in parallel with an electrical component.

5. Ammeter

• An ammeter is an instrument used to measure current in a circuit.

• It is connected in series.

6. Three-pin Plug• A plug is used to safely connect an appliance

to the mains socket.

• Plugs are mainly used in A.C.

• A 3-pin plug has 3 terminals:

– Earth wire – colored green/yellow insulation

– Neutral wire – blue insulation

– Live wire – brown insulation

7. Capacitor

• A capacitor is a device that stores energy in form of electrostatic energy (electrostatic field)

8. Thermistor

• A thermistor is a device whose resistance changes with temperature.

• As temperature increases, resistance reduces.

• Thermistors are used in fire alarms, digital thermometers and other temperature sensitive circuits.

9. Diode

• A diode is a device that allows current to flow in one direction only.

• It also called a rectifier.

• It is used to convert A.C. into D.C.

10. Transistor

• This is a device used to amplify signals. It also works as a switch.

• It has 3 terminals

– Base

– Emitter

– Collector

NPN transistor

SWITCH: the transistor can ONLY switch on when there is a small base current.when the transistor is on, it conducts current and allows current from the collector tothe emitter.

AMPLIFICATION: a small base current is amplified into a large collector current.