Magnetic Effects of Electric Current

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Magnetic effect of electric current is one of the major effects of electric current in use, without the applications of which we cannot have motors in the existing world. A current carrying conductor creates a magnetic field around it, which can be comprehended by using magnetic lines of force or magnetic field lines. The nature of the magnetic field lines around a straight current carrying conductor is concentric circles with centre at the axis of the conductor. The direction of the magnetic field lines of force around a conductor is given by the Maxwell’s right hand grip rule or the right handed cork screw rule.

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The strength of the magnetic field created depends on the current through the conductor. If the conductor is in the form of a circular loop, the loop behaves like a magnet. If the current in the loop is in the anticlockwise direction, a north pole is formed and if the current is in the clockwise direction a south pole is formed.

A current carrying conductor in the form of a rectangular loop behaves like a magnet and when suspended in an external magnetic field experiences force. The direction of the force is given by Fleming’s left hand rule.

This gives the basis for an electric motor. An electric motor essentially consists of a coil as an armature, a split ring commutator for changing the direction of the current in the coil. There are two brushes linked with the split rings that maintain the contact with the armature for the current flow.

Electric motor converts electrical energy to mechanical energy. A number of such loops form a coil and the coil is termed solenoid. If there is a soft iron core in the solenoid, it behaves like a magnet as long as there is current through the coil. Thus it is an electromagnet.

Electromagnetism created a revolution by leading to the devices called motors which convert electrical energy to mechanical energy. Experiments by scientists like Oersted and Faraday made a long leap by converting mechanical energy to electrical energy. When a straight conductor is moved in a magnetic field an electric current is induced in it and the phenomenon is electromagnetic induction. The emf caused is the induced emf and the current is induced current. Oersted found the same by relative motion of a magnet with respect to a coil.

Faraday's experiment proved that the strength of the induced current depends on several factors like the strength of the magnet, the speed of motion of the magnet, its orientation, the number of turns in the coil and the diameter of the coil. The induced current can be detected by a galvanometer. Fleming’s right hand rule gives the direction of the induced current in a conductor when it is moved in a magnetic field. Transformers are based on this principle, which consist of a primary coil and a secondary coil.

The number of turns in the coils is selected based on the type of the transformer to be made, namely, step-up or step-down. | Electric generators work on the same principle. They have an armature which is free to rotate in a magnetic field. Its terminals are connected to two slip rings, which are further connected to two brushes and they are connected across a load resistance through which the generated electricity can be trapped. The rotation of the armature in the magnetic field changes the magnetic flux in the coil of the armature and an electric current is induced.

For every half rotation, the direction of the induced changes and hence called alternating current. The current at the power plants is distributed through transmission lines at a high voltage and hence the lines are referred to as high tension power lines. At the substations these are stepped down to a lower voltage and supplied to houses at a low voltage. A domestic electric circuit essentially contains mains, a fuse, live or line, neutral and earth wires. From the poles supply cables bring the current to the mains.

Within the house, all the equipments are connected in parallel combination| | Electricity is one of the oldest branches of science without which we cannot just imagine ourselves in the current world. The rate of flow of charge through a conductor is termed the electric current and is measured in ampere. The potential difference across the conductor causes the charge flow between them. The potential difference is measured in volt and is the work done in moving a unit positive charge between two points in an electric field.

It implies that one joule per coulomb is one volt. In circuits potential difference is measured using a voltmeter and the current by an ammeter. The current flow from a high potential area to a low potential area is termed the conventional current whereas the flow of electrons constitute the electron current and is in a direction opposite to that of the conventional current. | As per electricity, we have two categories of materials, namely conductors and insulators. All of the conductors do not conduct electricity the same way.

Some of them offer a restriction to the flow of charge and are referred to as resistors. The restriction to the flow of charge is electrical resistance and depends on the physical dimensions and temperature of the conductor. The resistance (R) of a conductor varies directly with its length (l) and inversely with its area of cross-section (A). The mathematical expression is where ‘r’ is the constant called resistivity or specific resistance of the material which depends on the nature and temperature of the material.

Resistivity is measured in ohm-metre. At a given temperature, the current through a conductor is directly proportional to the potential difference across its ends and is known as Ohm’s law. | An electric circuit is a closed path for flow of electricity through which electricity can be converted into different forms. An electric circuit basically contains a source of electricity, a load resistance, a switch or a key for making the circuit on or off at ones convenience (which makes or breaks the circuit correspondingly).

The diagrammatic representation of an electric circuit is called the circuit diagram. Each electric component in a circuit has a unique symbol through which it is represented in a circuit diagram. If a circuit is switched off, it is called an open circuit and if the circuit is switched on it is called a closed circuit. When two or more resistors are connected such a way that the terminus of one resistance is connected to the starting end of the other, such a combination of resistance is called the series connection and the circuit is called series circuit.

On the other hand, if the starting ends of two resistors are joined to a point and the terminal ends of the two are combined and given connection to a source of electricity, such a combination is called parallel connection and the circuit is called parallel circuit. The potential difference or voltage drop across a resistance is the cause of electric current through it. For a number of resistors connected in parallel, the electric potential drop across them remains the same and the electric current through each of them varies as their resistance.

Heating effect of electricity is one of the widely used effects in the world. When electric current is passed through a conductor, it generates heat due to the resistance it offers to the current flow. The work done in overcoming the resistance is generated as heat. This is studied by James Prescott Joule and he enunciated various factors that affect the heat generated. The heat produced by a heating element is directly proportional to the square of the electric current (I) passing through the conductor, directly proportional to the resistance (R) of the conductor, time (t) for which current passes through the conductor.

It is given by the expression H = I2Rt and is well known as Joule’s Law. | Applications of the heating effect of electric current include appliances like electric immersion water heater, electric iron box, etc. All of these have a heating element in it. Heating elements are generally made of specific alloys like, nichrome, manganin, constantan etc. A good heating element has high resistivity and high melting point. An electric fuse is an example for the application of heating effect of electric current. The rating of 3 A of an electric fuse implies the maximum current it can sustain is three ampere. |