Railway Science (Physics-Electric Current and its Effects)

The right-hand thumb rule (Maxwell’s corkscrew rule) is a convenient way of finding the direction of the magnetic field associated with a current-carrying conductor. If the thumb of the right hand points along the direction of the current, the curled fingers of that hand give the direction of the magnetic field due to the current.

Direct current (DC) motor is an electrical machine which converts electrical energy into mechanical energy. DC motor working principle - When a current carrying conductor is placed in a magnetic field, it experiences a mechanical force. Fleming's left-hand rule and its magnitude decide the direction of this force. Major types of DC motor - Series DC motor, shunt/parallel DC motor, compound DC motors, permanent magnet DC Motor. Speed of a DC motor (N) is equal to N = K (V – IₐRₐ)/ ø Where, K is a constant.

Heating effect of Electric Current - When current flows through a conductor, heat energy is generated in the conductor. Heating effect produced by an electric current (I), through a conductor of resistance (R), for a time (t), is given by H = I²Rt. Example - Electric Iron, Electric heater, Electric geyser, Induction Cooker, Microwave Oven, Hair blower. Electric generators - work on the principle of electromagnetic induction.

Filaments of lamp bulbs properties: high temperatures and it has a high melting point, high resistivity, do not oxidize easily at high temperatures, ductile in nature. For example - Tungsten. Gas used in light bulbs - argon, helium, neon and nitrogen.

When the number of magnetic lines of force (magnetic flux) passing through a circuit/coil changes an electromagnetic force (emf) is produced in the coil, it is called induced emf. When the bar magnet is pulled away from the coil, the magnetic field linked with the coil decreases. So the induced potential difference in the coil will decrease.

When an electric current is passed through a conductor, it generates heat due to the hindrance caused by the conductor to the flowing current. DC motor - Converts electrical energy into mechanical energy. The electric iron was invented in 1882, by Henry Seely White. The DC motor works on the principle of “Faraday's law of electromagnetic induction".

The Earth has its own magnetic field. A freely suspended magnet always rests in the north-south direction because the magnetic south pole of the earth lies in the geographic north direction and the magnetic north pole of the earth lies in the geographical south direction. As unlike poles attract and like poles repel, a magnet aligns itself in north-south direction.

The strength of a magnetic field is represented by the closeness of the magnetic field lines. The closer the field lines are, the more is the strength of the field. Away from a current-carrying loop, the intensity of the magnetic field decreases. Right hand thumb rule states that if a current-carrying wire is assumed to be grabbed in the right hand in such a way that the thumb shows the direction of current then the curled fingers show the direction of the magnetic field.

Resistance is a measure of the opposition to current flow in an electrical circuit, it is directly proportional to Temperature. As the temperature increases, the value of resistivity increases so resistance increases. The greater the value of resistance, the more energy used by that resistor and the Higher the voltage drop across that resistor.

Induction of electric current in a coil due to changing magnetic flux is called electromagnetic induction. When a magnet is moved towards or away from the coil then due to the relative movement between the magnet and the coil an electromotive force (EMF) is induced which in turn causes the current in the coil. Current is induced only during the relative motion and as the movement stops the current flow will also stop. Changing magnetic flux is the main cause of the induction of current in the coil.