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

Galvanometer: This device is used on electrical circuits to measure the intensity and direction of electrical current. Voltmeter: Measures voltages of either direct or alternating electric current on a scale. Rheostat: A variable resistor which is used for controlling the flow of electric current either by increasing or decreasing the resistance.

Other Symbols

Electrical circuit is a network of electrical components with closed paths or loops in which electrons can flow. Flow of current: In solid - electrons are passed from one positively charged metallic atom to the next. In solution - the electron is carried by the ions present in the solution. A solution capable of carrying charge (electric current) is called an electrolyte.

Heating effect of electric current: When a current is flowing in a circuit having resistance there is a heat dissipation due to the resistance. Heat dissipated (H₁)= I² R t, Where I = the current flowing in the circuit, R = the resistance of the circuit, and t = the time taken.

I = Current R = resistance, V = voltage, t = time during which energy dissipated According to Ohm's law, resistance (R) = 𝑉/I.
H = energy dissipated in the resistance in the form of Heat.
H = I²Rt ⇒ H = I² × 𝑉/I × t
H = Vlt.

By Ohm's law, V = IR, where V = voltage, I = current, and R = resistance.
R = , ρ × 𝐿/A , Where, R = Resistance,  ρ = Resistivity, L = Length of material and A = cross sectional area of material. When the length (L) of the wire is doubled, Resistance (R) is also doubled and so, current (I) is halved.

The materials that allow electricity to flow through them, Good conductor - Those materials which allow electricity to pass through them easily; Example - Copper, steel, gold, silver, platinum. Bad conductor - Those materials which do not allow electricity to pass through them; Example - Glass, plastic, rubber and wood.

A circuit is said to be parallel when the electric current has multiple paths to flow through. The components that are a part of the parallel circuits will have a constant voltage across all ends. Other components will function even if one component breaks down, each has its own independent circuit. A series circuit is a circuit in which two components share a common node and the same current flows through them. If one component breaks down, the whole circuit would burn out.

The total Resistance (series combination), Rₙₑₜ = R₁ + R₂ = = 4 Ω + 6 Ω = 10 Ω.
The total Current in the circuit, I = 𝑉/R = 5 volt/10Ω = 1/2 A.
The Potential drop across resistance 4 Ω is given as V= IR = 1/2 × 4 = 2V.

(Resistivity) R =  ρ  𝑙/A,
Given, R₁ = ρ 3𝑙/2A. After comparing both,
R₁ = 3/2 R