Electricity — Ohm's Law, Series vs Parallel and the Household Circuit

Electricity is the single most reliable scoring chapter in school-level physics, and it turns up in TRE-4 General Studies, CTET Science, SSC CGL, RRB NTPC and every state TET. The reason is that almost every question is one substitution into one of five formulas.

Start with the three quantities.

CHARGE (Q), measured in coulomb (C). Q = I × t. One coulomb is the charge carried by about 6.25 × 10¹⁸ electrons, because one electron carries 1.6 × 10⁻¹⁹ C.

CURRENT (I), measured in ampere (A). Current is the rate of flow of charge: I = Q / t. One ampere is one coulomb per second. Conventional current flows from the positive to the negative terminal — the opposite of the actual direction electrons move.

POTENTIAL DIFFERENCE (V), measured in volt (V). V = W / Q, work done per unit charge. One volt is one joule per coulomb. It is measured with a voltmeter, which is always connected in PARALLEL across the two points.

1. A 6 Ω resistor and a 3 Ω resistor are connected in parallel. What is the equivalent resistance of the combination?

2. One kilowatt-hour, the commercial unit of electrical energy, is equal to how many joules?

3. How are an ammeter and a voltmeter connected in a circuit?

4. Domestic appliances in a house are connected in parallel rather than in series mainly because

5. Why is nichrome, and not copper, used as the heating element in an electric iron or a room heater?

6. What is the resistance of the filament of an electric bulb rated 100 W, 220 V when it is working?

7. In a domestic electric circuit, the fuse is always connected in which wire?

8. A uniform wire is stretched so that its length becomes double and its area of cross-section becomes half. Its new resistance will be