Railway Science (Physics-Electric Current and its Effects)

Electromagnetic induction - Production of an electromotive force across an electrical conductor in a changing magnetic field. Isaac Newton - Law of Gravity (every particle attracts every other particle in the universe with a force that is proportional to the product of their masses and inversely proportional to the square of the distance between their centers). Albert Einstein - Theory of relativity. Alessandro Volta - Voltaic pile (electric battery).

The direction of induced current in a straight conductor is given by Fleming’s right hand rule. It states that if we stretch the thumb, forefinger and the middle finger of the right hand at right angles to one another in such a way that the forefinger points in the direction of the magnetic field. Then, the thumb gives the direction of motion of the conductor (force),and the middle finger points the direction of induced current.

Resistivity - a property that describes the extent to which a material opposes the flow of electric current through it. It is a property of the material itself (independent of the size or shape of the conductor). SI unit - ohm meter (Ωm). The resistivity of alloys is generally higher than that of pure metals. Metals - good conductors - low resistivity. Insulators - Very high resistivity. Conductivity is the inverse (reciprocal) of resistivity. Resistivity is directly proportional to Resistance.

It states that if we arrange our thumb, forefinger and middle finger of the right-hand perpendicular to each other, then the thumb points towards the direction of the motion of the conductor relative to the magnetic field, the forefinger points towards the direction of the magnetic field and the middle finger points towards the direction of the induced current. In electromagnetism, It shows the direction of induced current for generators.

Fleming’s Left Hand Rule: Used to find the direction of the force. If we keep the index finger in the direction of the magnetic field, and the middle finger in the direction of current, which is in the direction in which the proton is moving (since it is positively charged), the direction in which the force is experienced by it will be in the direction of the thumb, which is pointing into the plane of the paper.

Solenoid - A wire coil that works as an electromagnet when electricity flows through it. The magnetic fields of a solenoid are determined by the density of coils, the number of turns, and the current flowing through it. Since the magnetic field lines inside it are parallel and equidistant which means the strength of magnetic field is uniform inside the solenoid.

Factors affect the force on a current carrying conductor - Strength of magnetic field, Current flowing through the conductor, Length of the conductor. The direction of the force can be determined by using the Fleming's Left-Hand Rule. Direction of force changes by reversing the direction of the magnetic field.

Facts regarding magnetism - The earth behaves as a magnet, Magnetic monopoles do not exist, magnetic field lines of a magnet (or a solenoid) form continuous closed loops, magnetic field lines do not intersect, if they intersect then it will have two directions of magnetic field at the same point of intersection which is not possible.

The field lines inside the solenoid are in the form of parallel straight lines which means that the magnetic field is the same at all points. Like the bar magnet, the field lines emerge from one end and merge at the other end. It means one end behaves like the North pole while the other end behaves like the South pole.

Magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. The direction of the magnetic field at a point can be found by placing a small magnetic compass at that point. The north end of the needle of a compass indicates the direction of the magnetic field at a point where it is placed. The magnetic field lines are densest at the center and least dense between the two poles just outside the bar magnet.