PART TWO!

Description :

Conductors ; an electrical conductor is a material that allows electricity to flow through easily.

Insulators ; is a material that electricity cannot flow through easily.

Units used to measure :

Current --> I ( ampere )
Voltage --> V
Resistance --> Ohm

Resistors

Resistors are used to protect other components from being damaged by reducing excessively high currents in the circuit.

A breadboard allows circuits to be built and tested quickly and easily.
- components are simply pressed into the holes in the breadboard.
-connecting tracks underneath the surface are shown the the thin lines.

A transistor is an automatic switch.
- can be used for sensing circuits

The base of the transistor is usually connected to a sensor. If the sensor allows enough current to flow, the transistor switches on.

-Moisture sensing circuits are useful in various situations such as :

- checking the dampness of soil for a potted plant, raising an alarm when it rains. ( pg 21 of notes)

Light sensing circuits are useful in various situations such as :

- switching lamps on automatically in the dark and setting off alarms when a beam of light is broken.

- uses a component called a LDR ( light dependent resistor ), which is connected to the base of the transistor.

For extra sensitivity, 2 transistors may be used.
2 transistors connected in this way is called Darlington Pair.

Temperature sensing circuits are useful in various situations such as :
-switching electric kettles off automatically.

Temperature sensing circuits use a component called a thermistor, which is connected to the base of the transistor.
- The value of a thermistor is a measure of its resistance at room temperature 25 oC

The sensivity of the temperature sensing circuit can be changed by adding a potentiometer.
- with the potentiometer connected, the circuit may be adjusted to switch on the transistor when the temperature reached a preset range.

Thyristors

are used in alrm systems. Once triggered, the switch remains on until they are rest manually.

Ways to reset a thyristor --> disconnect the power supply for a moment.

Capacitors

-Store electricity, like rechargeable batteries.
-Electrolytic capacitors can only be connected one way, but non electrolytic capacitors can be connect either way round.

Equipment used to measure :

Voltage --> voltmeter
Current --> ammeter
voltage, current and resistance --> multimeter.

Mains power has the alternating current (AC) which means that the flow of electricity continually changes direction in a circuit.

- Many electrical products require a direct current (DC) supply, which constantly flows in one direction.

Solar panels are another form of power supply.
These convert energy from light into electricity.

Types of switches

Slider switch ; on/off switch for toys and electronic games.

Rocker swicth ; light switches, electrical sockets.

Rotary switch ; ceiling fans, volume control of a radio to serve as an on/off switch.

Push switch ; Calculators, telephones, computer keyboards.

Micro swicth ; workshop machinery, microwave cookers, washing machines.

Reed switch ; connected and separated by a magnetic field.
- Security alam systems use reed swicthes to detect the opening of a door which activates a siren.

Tilt switch has a small drop of mercury inside it which connects two contacts together. As the switch is tilted, the mercury falls away from the contacts and creates a break in the circuit.

Key switch is a special type of rotary switch.
E.g car ignition systems.

Membrance panel switches ; Microwave ovens, cash dispensers, photocopiers.

OFF TO SHOWER & TO SCHOOL, BYEBYE!