MAGNETIC EFFECTS OF

ELECTRIC CURRENTBY AMAN SHARIF

WHAT IS MAGNETIC EFFECT ?

A magnet is a substance which has a tendency of attracting some metals when placed near it. When a linear piece of magnet suspended freely then it always align in north – south direction. The end of bar magnet pointing towards north is called North Pole; while the other end of magnet pointing towards the south ,is called South Pole.

PROPERTIES OF MAGNET:

The ends of a magnet where the magnetic effect is maximum is called three poles of a magnet. A magnet has two poles- North Pole and South Pole.

When a magnet is suspended freely it always comes to rest in North – South direction.

The magnetic poles exert forces on each other .Like poles repel and unlike poles attract each other .

Magnetic poles always exists in pairs.

Repulsion is sure test of magnetism.

MAGNETIC COMPASS:

Magnetic compass is simple device to find the direction .It is a small magnet which is pivoted at its centre so that it can rotate freely in its horizontal plane. It always points towards North – South Direction.

MAGNETIC FIELDS:

The region around a magnet in which the force of the magnet can be experienced is called its magnetic fields.

Magnetic fields is of two types:

a) UNIFORM MAGNETIC FIELD: If the magnitude and direction of magnetic field is same at every point then field is said to be uniform magnetic field.

NON UNIFORM MAGNETIC FIELD: If the magnitude and/or direction of magnetic field is not same every point then field is said to be non uniform magnetic field.

MAGNETIC FIELD INTENSITY: Magnetic field intensity at a point is defined as the force experienced

by an isolated unit North Pole placed at that point. S.I unit of magnetic field intensity is tesla (T).

MAGNETIC LINES OF FORCE OR FIELD LINES :

These are imaginary lines along which the magnetic field acts. Magnetic lines of force is curve or line along which an isolated north pole compass would move, if free to do so, in the given magnitude field. Tangent to it at any point gives the direction of intensity or force at that point.

PROPERTIES OF MAGNETIC LINES OF FORCE:

Magnetic lines of force moves from North poles to South poles outside the magnets and from South pole to North pole inside the magnet. So magnetic lines of force are closed continuous curves.

Tangent to magnetic lines of force at any point gives the direction of magnetic field at that point.

No two magnetic lines of force can intersect each other ,because is two magnetic lines of forces can intersect each other at any point, then at that point, we have to draw tow tangents, which is not possible.

In a region ,where magnetic field is stronger , magnetic lines of forces are crowded; while thinning of lines of force means region is weaker field.

Magnetic lines of force contract longitudinally and dilate laterally.

MAGNETIC FIELD DUE TO BAR MAGNET

Magnetic fields due to bar magnet can be finding either using iron fillings or by using a compass needle.

MAGNETIC EFFECT OF ELECTRIC CURRENT:

When electric current is passed through a conductor ,magnetism is produced around it and the conductor acts like a magnetic effect of current.

SNOW RULE: If current flows from South to North ,when conducting wire is held over the magnetic needle, then the North Pole of needle deflects towards the West. If the direction of the current is reversed ,then the direction of deflection is also reversed.

AMPERE’S SWIMMING RULE: Imagine a man is swimming along the wire in the direction of flow of the current with his face always turned towards the magnetic needle, and then the north of the magnetic needle will get deflected towards his left hand.

MAGNETIC FIELD DUE TO A STRAIGHT CURRENT CARRYING CONDUCTOR : The shape of magnetic fields due to a straight current carrying

conductor is concentric whose axis is the current carrying conductor.

RIGHT HAND THUMB RULE:

Grasp the wire in the right hand so that the thumb points along the wire in the direction of the current ,then the direction in which fingers encircle the wire gives the direction of the magnetic field.

MAGNETIC FIELD DUE TO A CURRENT CARRYING CIRCULAR LOOP: The strength of magnetic field produced by a circular coil containing

current can be increased by-

a) Increasing the number of turns of wire in the coil.

b) Increasing the current flowing through the coil and -.

c) Decreasing the radius of the coil.

CLOCK RULE:-

The polarity of any face of coil can be known by clock rule. According to clock rule if the current round any face of the coil flows in anticlockwise direction it behaves like a north pole and if the current flows in the clockwise direction, the face acts as a south pole.

MAGNETIC FIELD DUE TO A SOLENOID:

A Solenoid can be defined as a long coil of many circular turns of insulated metal wire wrapped closely in the shape of cylinder such that its length is very large as compared to its diameter.

When current is passed through such a Solenoid ,a magnetic field is produced around and within it. The end of the solenoid at which current flows in the anticlockwise direction behaves as a magnetic north pole and other end of the solenoid at which current flows in clockwise direction behaves as the magnetic south .

The magnetic field pattern due to solenoid is very much similar to that of a bar magnet.

The magnetic field inside the solenoid is uniform and outside its is non-uniform .The direction inside the solenoid is from south to north pole and out side it is from north to south pole.

On reversing the direction of current flowing in the solenoid the north pole and the south pole get interchanged.

Strength of magnetic field produced by a current carrying solenoid depends upon:

a) Number of turns: Larger the number ,stronger is the magnetic field produced.

b) Strength of current: Larger is the amount of current ,stronger is the magnitude field.

c) Nature of core: Strength of magnetic field also depends on nature of core material.

ELECTROMAGNETS:

Electromagnet is essentially a soft iron core, embraced by a current carrying insulated coil. It produced strong magnetic field when a current flows through it.

DIFFERENCE B/W AN ELECTROMAGNET AND PERMANENT MAGNET: ELECTROMAGNET

Its is temporary as it exhibits magnetic force only, when current flows through it.

It can produce very strong magnetic force.

Its strength can be changed.

Its polarity can be changed.

PERMANENT MAGNET

It is a permanent magnet.

It produces comparatively much weaker magnetic force.

Its strength cannot be changed.

Its polarity cannot be changed.

FORCE ON A CURRENT CARRYING CONDUCTOR IN A MAGNETIC FIELD:

When a current carrying conductor is placed in a magnetic field, it experiences a force on it.

The strength of force depends on:-

The strength of the electric current flowing through the conductor.

The length of the conductor .

The strength of magnetic field.

The sine of the angle between current and magnetic field.

The force is max- when the angle between current and magnetic field is 90* and it is mini- when angle is 0*.

The direction of the force can be find by Fleming’s Left Hand Rule. According to it: Stretch the thumb, the forefinger and the middle finger of your let hand such that they are mutually perpendicular to each other .If forefinger points in the direction of the magnetic field and the middle finger in the direction of the current , then the thumb will point in the direction of force

ELECTROMAGNETIC INDUCTION (EMI):

The phenomenon of the production of induced current in a circuit, due to change in magnetic field linked with it (called flux), is called electromagnetic induced current depends on the rate by which the magnetic field linked with the coil is changing .Current can be induced in a coil when:-

o There is a relative motion between a coil and a magnet.

o A magnetic field linked through a coil is changed by rotating the coil.

o When a current or magnetic field changes in a coil which is laced in the near of the given coil (in which current is to be induced).

The direction of induced current can be obtained by Fleming’s right hand rule.

If we stretch the right hand such that forefinger, central finger and thumb are mutually perpendicular to each other. If the forefinger indicates the direction of the magnetic fields and thumb shows the direction of motion of the conductor, then central finger gives the direction of induced current.

DIRECT AND ALTERNATING CURRENTS: DIRECT CURRENT:- DC always flows in the same direction.

ALTERNATING CURRENT:- AC is one in which the direction of current changes periodically and value changes continuously. In India frequency of AC is 50 Hz and Rms voltage is 220 volt. It means the current changes its direction after every 1/100s.

ADVANTAGES OF AC OVER DC:

a) AC can be transmitted over a long distances.

b) AC can be converted into DC.

c) AC is easier and cheaper to generate.

d) The magnitude of AC can be easily increased or decreased by using transforms.

e) The cost of transmission of AC power is low.

DISADVANTAGES OF AC OVER DC:

a) AC is much dangerous to work as compare to DC as it gives severe shock.

b) AC cannot be use in electroplasting.

DOMESTIC ELECTRIC SUPPLY:

The electricity supplied to our homes is AC of 220 V having frequency 50 Hz.

In homes there are two types of circuits: Lighting circuits with 5 A fuse (for electric bulbs, fans, tube lights etc.) and power circuits with 15 A fuse (for room heaters, refrigerators ,air conditioners etc.)

While connecting the two distribution circuits with the main supply ,each circuit is connected in parallel.

A COMMON DOMESTIC ELECTRIC CIRCUIT CONSISTS OF:

MAIN BOARD:- It is provided outside the house .It contains the main fuse and the meter. The ends of the cables from the street electric pole are connected to the two terminals of electricity board fuse. This fuse is further connected to an electricity meter for measuring the consumption of electricity energy. The electric cable coming to the house consists os three separate insulated wires; live wire or phase wire( red in colour) ,Neutral wire (black in colour) and the earth wire(green in colour). The potential difference between live and neutral wire is 220 V.

DISTRIBUTION BOX:- It contains main switch and fuses for each circuit. In main switch live wire and neutral wire from electric meter are further connected .By switching off the main fuse, the electricity supply to the house can be cut off completely when required. After that elericity is distributed to different part of the house through various distribution circuit is provided wit a separate fuse in live wire.

ROOM WIRING:- All electrical appliance are connected across the neutral and live wires in parallel so that :-

i. Same potential difference acts across all of them .

ii. Any electrical appliance may be switched on or off with out any interference to the other .

iii. It is one of the appliance gets fused ,it will not affect the working of other appliance.

iv. Each appliance has a separate ON/OFF switch to control the flow of current through it. The switch is always connected in live wire.

v. Most of the domestic appliance are connected to the main by means of sockets ( a three pin plug ). The three brass cylindrical pins are fitted on a socket. The lower terminals which are smaller in length and diameter are fore live wire (right one ) and neutral wire (left one) .The upper terminal which is longer and thicker diameter is connected to the earth wire.

ELECTRICAL PROBLEMS: OVERLOADING:- All electrical appliances and wires used in the circuit

have a definite power rating .If the appliances connected through the wire draws more current than its safety limit, the wire gets heated. This fault is called overloading. Due to this ,wire gets heated to a very high temperature anf=d sometimes melts or burns.

SHORT CIRCUITING: Sometimes due to defective wiring or improper insulation of wires,

the live wire comes in the direct contact with the neutral wire. Due to this the resistance of the circuit becomes very small and a large amount of current flows through the circuit causing overheating .This is called short circuit. Overheating due to short circuit damages the appliances or may cause electric fires.

ORECAUTIONS TO AVOID THE OVERHEATING AND SHORT CIRCUITING OF DOMESTIC ELECTRIC CIRCUITS:-

1. All wires used in electrical circuit should have good quality insulation and proper amperage.

2. All joints of naked wires should be covered with insulating tape.

3. Immediate replacement or repair of the damaged or defective wire, switches, plugs and sockets etc. should be done.

4. Fuse of proper rating and material should be used.

5. All connections at switches ,sockets, plugs must be tight to avoid sparking.

SAFETY MEASURES: EARTHWIRE:- It is used as a safety measure especially for those

appliances that have a metallic body and are frequently touched by us with bare hands. The earth wire comes from the earthling pit prepared near the house. It is connected to the main switch from where it goes along the live and neutral wires from the main board. Now when an electric appliance is connected to the electricity supply line through the three pin plug, the green coloured earth wire keeps the appliance set zero potential. Also the thick wire used as earth wire can carry a large current in case of short circuiting or over heating and ensure that any leakage of current to the metallic body of the appliance, floes directly to the earth and the used does not get and electric shock.

FUSE:- It is the most common safety device .A fuse in the circuit prevents

damage to the appliance and the circuit in the case of overload and short circuit which may be caused due to faulty wiring or use of poor quality wires or voltage fluctuations . A fuse is based on the joules law of heating. It has a wire of low malting point which melts in passing high current and brakes the electric circuit , thereby stopping the flow of current and protect the appliance from getting damaged.

THANK YOU .