BY

RITA KHAPEKAR, TGT SCIENCE , JNV MANPUR INDORE

NAVODAYA VIDYALAYA SAMITI, NOIDA

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E-CONTENT PREPARATION

CLASS – VII SCIENCE

CHAPTER – 14

Electric Current and its Effects

ELECTRIC CURRENT AND ITS EFFECTS

• PREPARED BY:
• RITA KHAPEKAR
• TGT SCIENCE JNV MANPUR INDORE
• MADHYA PRADESH

LEARNING OUTCOME

• AFTER THE COMPLITION OF THIS CHAPTER STUDENTS WILL BE ABLE TO:
• IDENTIFY SYMBOLS OF ELECTRICAL COMPONENTS
• DRAW ELECTRIC CIRCUIT DIAGRAM USING SYMBOLS
• DIFFERENTIATE BETWEEN OPEN AND CLOSED CIRCUIT

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• EFFECTS OF ELECTRIC CURRENT :
• HEATING EFFECT
• MAGNETIC EFFECT
• USES OF HEATING EFFECT IN OUR DAILY LIFE
• USE OF SAFETY FUSE
• ELECTROMAGNET
• CONSTRUCTION AND WORKING OF ELECTRIC BELL

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Introduction�

• Electricity is form of energy which can be converted into light, sound or heat energy,etc.
• Electric is generated due to the movement of electric charges i.e. positive (+ve) and negative (-ve) charges from their sources.
• The sources of electric current are cells or batteries.
• The SI unit of electric current is ampere (A) and that of charge is coloumb(C).
• The electric current flows from its source through the conducting material only. A material set to be good conductor of electricity if it allows electric current to flow or pass easily through it for example the metals like iron, copper, aluminium in their solid states or salt solutions, acid solution, alkali solution, water etc. are good conductors of electricity. Thematerials through which electricity cannot pass or flow easily are known as bad conductors of electricity. For example plastic, wood,rubber,wax, paper etc. The bad conductor of electricity are also called insulator.

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Electric circuit

• An electric circuit is a path through which current flows. An electric circuit may be a complete electric circuit ( closed circuit) or incomplete electric circuit( open circuit)

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Types of circuit��CLOSED CIRCUIT�

In a closed electric circuit , the electric current starts from the

positive terminal of the source and ends at the negative terminal of the

source without any break. The current flows only ifthe circuit is complete or closed,all the elements of the electric circuit start functioning.

• In an open electric circuit, the electric current starts from the positive terminal of the source but does not reach the negative terminal of the source because the circuit is broken at some point. In the open circuit, current does not flow and the elements /components of the electric circuit do not work.

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OPEN CIRCUIT

COMPONENTS OF ELECTRIC CIRCUIT

• Elements/Components of Electric Circuit:The parts which constitutes an electric circuit are called elements of electric circuit.A source(cell or battery),connecting wire,an appliance(bulb,fan,heater etc.),The key(switch)

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SYMBOLS OF ELECTRIC COMPONENT

• Source of electricity is a cell or a battery.There may be one or more source of circuit.Combination of cells may be in series or a parallel.
• Connecting Wires:These are normally conducting materials covered with insulating materials like plastics or rubbers.Forexample,copperwire,aluminiumwire,etc.
• An Appliance:It is a device which uses the current.Forexample,electricbulb,fan,heater,etc.
• A key:This is the switch by which we can close the circuit or open (break) it.

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TYPES OF EFFECTS OF ELECTRIC CURRENT

• Effects of electric current:When an electric current is passed through an electric circuit,it may produce the following effect:--

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• HEATING EFFECT
• LIGHTING EFFECT
• MAGNETIC EFFECT
• CHEMICAL EFFECT

Heating effect of electric current:

When electric current flows through a conductor, some heat is produced(due to resistance of the conductor).This effect of current is known as heating effect of electric current.

Heat produced in a conductor by an electric current depends on:

1. Length of the conductor

2. Thickness of the conductor

3. Nature of the material of the conductor

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• In our daily life, there are many applications of heating effect of electric current. The working of electric bulb ,electric iron ,electric heater, room heater, and many other electric appliances is based on the heating effect of electric current.
• The wires used for making electric circuits do not normally becomes hot. On the other hand ,the elements of some electric appliances become so hot that they are easily visible. The Filament of an electric bulb gets heated to such a high temperature that it starts glowing.
• An electric bulb is used for light but it also gives heat. This is not desirable. This results in the wastage of electricity. This wastage can be reduced by using fluorescent tube lights in place of the bulbs .Compact fluorescent lamps (CFLs)also reduces wastage and can be fixed in the ordinary bulb holders.

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Short circuit

• The short circuit is generally caused due to the accidental connection of live wire (positive and negative terminal) with the earth wire or the neutral wire.

Overloaded electric circuit

• A circuit is said to be overloaded when more current passes through the circuit than it can tolerate without heating the conducting wires. Overloading of circuit occurs due to a large current, short circuit or fluctuation of voltage.

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SAFETY FUSE OR ELECTRIC FUSE

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• The Fuse is a safety device making use of the heating effect of electric current.
• It is used to protect electric circuits and electric appliances against high current. High current flows through the circuit because of shortcircuit or random voltage fluctuations. When high current flows in a circuit, it is called overloaded circuit.

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• 1.Kit-Kat fuse: It is the combination of the porcelain fuse socket and a carrier.

• 2.CartridgeFuse: Cartridge fuse is made by putting a fuse wire inside a glass tube and connecting its two ends to a metallic caps fitted tightly over the glass tube.
• These type of fuses are used to protect sensitive electronic appliance from excessive current.

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3. Miniature Circuit Breaker(MCB):MCB is also a type of safety device which is connected in the electric circuit. Unlike in fuse, the MCB stops the flow of current by simple ,turning OFF. To continue the current flow, one has to turn ON the MCB again.

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MAGNETIC EFFECT OF ELECTRIC CURRENT�

• In 1820 Danish Scientist Hans Christian Oersted discovered that the electric current has magnetic effect. The relationship between electricity and magnetism is known as electromagnetism.
• ELECTROMAGNET
• A coil wound around an iron core which acts as a magnet as long as electric current flows through the coil, is called an electromagnet.

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ELECTROMAGNETISM

USES OF ELECTROMAGNET

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• Electromagnets are used in many electrical appliances such as electric motors, electric fan, electric bell, etc.
• They are used in electric generators.
• Electro magnet are used in television for deflecting electron beam of the picture tube.
• They are used in magnetic separation of iron ores from earthly substances.
• They are used clinical apparatus to remove magnetic foreign bodies like iron filings from a patient’s body part.
• They are used to make permanent magnets.

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DIAGRAM OF ELECTRIC BELL

Electric Bell�

• Principle:It works on the principle of Electromagnetism.
• Construction and working: It consists of a soft iron armature mounted on a springy metal strip placed in front of a U-shaped electromagnet.
• The electromagnet is wound on an insulated copper wire of a large number of turns.one end of the insulated copper wire is connected to the T1 of the cell and the other end of the metal strips.
• The metal strip makes contact with one adjustable contact screw at contact point .
• A hammer made up of steel is attached to the armature.
• It also consists of a gone which is made of brass.
• When the bell operates, the hammer repeatedly strikes against the gong and produces the sound.

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SUMMARY

In this chapter you learnt about:

• Symbols used for electric components
• open and closed circuits
• Effects of electric current:heating effect and magnetic effect
• Uses of heating effect
• Electric fuse/safety fuse
• Types of safety fuse
• Magnetic effect of electric current
• Electromagnet
• How electric bell works?

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THAN YOU

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