Railway Science (Physics-Electric Current and its Effects) (Part-II)

Commutator - It reverses the direction of flow of current through a circuit. In a motor, the commutator applies electric current to the windings. By reversing the current direction in the rotating windings in each half turn, a steady rotating force (torque) is produced. Motor - Convert the electrical energy to mechanical energy. Generator - Convert the mechanical energy to electrical energy.

An iron rod. Whenever the number of magnetic lines of force (magnetic flux) passing through a circuit/coil changes an emf is produced in the circuit called induced emf. The induced emf is given by the rate of change of magnetic flux linked with the circuit as, e = emf = −N 𝑑Φ/𝑑t Where e is induced voltage, N is number of loops, dΦ is change in magnetic flux, dt is change in time. When the coil and a magnet are moved in the same direction and at the same speed, then there is no change in the magnetic field across the coil and hence no induced current.

Magnetic field - The force of magnetism acts on the area around a magnetic material or a moving electric charge. Magnetic field and electric field are interconnected and constituents of the electromagnetic force. If magnetic field lines intersect each other, then at the intersection point there will be two directions of the same field which is not possible. Unit of magnetic field - Tesla.

Fleming's Right Hand Rule - When arranging the thumb, forefinger and middle finger of the right-hand perpendicular to each other, then the thumb points towards the direction of the magnetic force, the forefinger points towards the direction of the magnetic field and the middle finger points towards the direction of the current.

A magnetic compass consists of a tiny magnetic needle (indicates the north-south direction when it comes to rest) attached to an aluminium pointer. The magnetic compass was invented in China between the 2nd century BC and the 1st century AD.

In a parallel combination, all the bulbs will have the same voltage as that of the battery but the current is divided among them. However, in a series connection, the voltage gets divided among all the bulbs but the current remains the same. So, the bulbs which are connected in parallel will glow brighter.

According to this Fleming's left-hand rule, stretch the thumb, forefinger and middle finger of your left hand such that they are mutually perpendicular to each other. If the forefinger points in the direction of the magnetic field and the middle finger in the direction of current, then the thumb will point in the direction of motion or the force acting on the conductor.

Factors Affecting magnetic lines - Number of turns in the solenoid, Current in the solenoid (Polarity of the solenoid changes according to the direction of current).

Using wooden rods as core material would not be effective for a solenoid as wood is not a good conductor of electricity and does not have high magnetic permeability. Magnetic field of solenoid is directly proportional to the current passing and the number of turns and has a proportionality constant which depends on the material of the conductor, instead of an area magnetic field depends upon the length of solenoid.

AC (alternating current) Generator - Converts mechanical energy into electrical energy in the form of alternating current. DC (Direct current) Generator - Converts mechanical energy into direct current. Both work on Faraday’s law of electromagnetic induction. Difference between AC and DC Generators on various factors : Direction of Current - Current reverses direction periodically (AC) / Current flows only in one direction (DC). Voltage Level - Generate very high voltages (AC)/ Generate lower voltages (DC). Rings - slip-rings (AC) / split-ring commutators (DC). Current induction - Current can be induced either in the rotor or in the stator (AC) / Current is induced in the rotor only (DC).