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

Electric circuit - Provides a complete path for electricity to pass between the two terminals of the electric cell. Types: Series circuit - There is only one path for electrons to flow in a series circuit. At a particular time, the entire circuit is either closed or open. Disadvantage - No current flow in the circuit in the event of a circuit break because the entire circuit is open. Parallel circuit - The circuit is connected across different branches in a parallel type of electric circuit. As a result, electron flow occurs in multiple stages. If a circuit break occurs in one path, electric current continues to flow in other paths.

Filament (Thin wire in an electric bulb that produces light) - Any material which has high resistivity and gets heated at a low temperature can be used as a filament. Tungsten is currently used to make filaments of the bulbs. Tungsten Properties: Very high melting point (3,422 ° C) and very high resistance, so it does not burn easily at room temperature.

An Ammeter is a device which is used to measure electric current in a circuit. It is always connected in series in an electric circuit.

Rubber, glass and plastic are insulators that do not allow electricity to easily pass through them. An electrical conductor allows the electric charges to flow through them easily. Typically, metals, metal alloys, electrolytes and even some nonmetals, like graphite and liquids, including water, are good electrical conductors.

When the switch is in ON position, current can flow through the circuit. When the switch is in OFF position, no current flows through the circuit. Switch was invented by John Henry Holmes in 1884. Famous Inventions and their Inventors: Electric cell - Alessandro Volta, Electric bulb - Thomas Alva Edison, Telephone - Alexander Graham Bell, Radium and Polonium - Marie Curie.

Resistance depends on length and area of cross-section. R= ρ l/A. l = length, A = area of cross section, ρ = resistivity. As we increase temperature, average speed of the electrons, which act as the carriers of current, increases resulting in more frequent collisions.

It provides a complete path for electricity to pass (current to flow) between the two terminals of the electric cell. When the circuit is open the electric current does not flow through it. When the circuit is closed the electric current flows through it.

Parallel circuit - It has two or more paths for current to flow through. Voltage is the same across each component of the parallel circuit. The sum of the currents through each path is equal to the total current that flows from the source. Series circuit - There will be only one path for electrons to flow in a series circuit. At a particular time, the entire circuit is either closed or open. Voltmeter - Measuring electric potential difference between two points. Ammeter - It is always connected in series to measure current. It has a low resistance.

Electric power is the rate at which work is done or energy is transformed into an electrical circuit. It is denoted by P, which is measured in SI units of joule per second or watt. The dimension of Power is ML²T⁻³. One Horsepower = 746 watts. One Volt is defined as the energy consumption of one joule per electric charge of one coulomb (1V = 1J/C). Dimension of voltage is [ML²T⁻³I⁻¹].

Substances which block the flow of electrical or thermal currents. Example - Rubber, Dry wood. Resistance - Property of a conductor by virtue of which it opposes the flow of electric current through it . SI unit of resistance - Ohm (Ω). Conductors - Material or substances which allow movement of electricity through them. Example - Gold, copper. Resistors - Electric components that limit or regulate the flow of current in a circuit. Example - fan speed controller. Superconductor - Material that conducts electricity with zero resistance. Example - Magnesium Diboride, Niobium.