Page 258 - Electrician - TT (Volume 2)

ELECTRICIAN - CITS

MODULE 16 : Domestic Appliances

LESSON 101-103 : Domestic appliances - electric heaters

electric cettle, geyser, washing machine

Objectives

At the end of this lesson you shall be able to:
• explain the domestic appliances
• explain the working principle and circuits electric heaters electric cettle
• explain working of electric iron, geysers, mixer, their dries
• state the concepts of netrual & earth.

Domestic appliences,based on heating effect

Effects of electric current
When an electric current flows through a circuit, its presence is judged by its effects, which are given below.
1 Chemical Effect
When an electric current is passed through a conducting liquid (i.e. acidulated water) called an electrolyte, it
is decomposed into its constituents due to chemical action. The practical application of this effect is utilized in
electroplating, block-making, battery charging, metal refinery, etc.

2 Heating Effect
When an electric potential is applied to a conductor, the flow of electrons is opposed by the resistance of the
conductor and thus some heat is produced. The heat produced may be greater or lesser according to the
circumstances, but some heat is always produced. The application of this effect is in the use of electric presses,
heaters, electric lamps, etc.
3 Magnetic Effect

When a magnetic compass is placed under a current carrying wire, it is deflected. It shows that there is some
relation between the current and magnetism. The wire carrying current does not become magnet but produces
a magnetic field in the space. If this wire is wound on an iron core (i.e. bar), it becomes an electro-magnet. This
effect of electric current is applied in electric bells, motors, fans, electric instruments, etc.
4 Gas Ionization Effect

When electrons pass through a certain gases sealed in a glass tube, it becomes ionised and starts emitting light
rays, such as in fluorescent tubes, mercury vapour lamps, sodium vapour lamps, neon lamps, etc.
5 Shock Effect
The flow of current through the human body may cause a severe shock or even death in many cases. If this
current is controlled to a specific value, this effect of current can be used to give light shocks to the brain for the
treatment of mental patients

Definitions
1 Electro motive force (emf)
The force which causes current to flow in the circuit is called emf. Its symbol is E and ismeasured in volts (V).
It can be calculated as:
emf = voltage at the terminal of source of supply + voltage drop in the source of supply

oremf = VT + 1R
2 Voltage
Voltage It is the electrical potential (i.e. pressure) between any two live wires or between one live wire and earth.
Its symbol is V and the unit of measurement is volts. It is also measured by a voltmeter.

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