Paper II · Part B — Physics

Electricity: Static, Current, Ohm's Law and Cells

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Concept

Static electricity is charge at rest; current electricity is charge in motion through a conductor. Ohm's law relates voltage, current and resistance. Cells provide the energy that drives the current.

Current has heating, lighting and magnetic effects.

Key Points & Formulas

Ohm's law: V = IR (volt = ampere × ohm).
Series: same current, resistances add (R = R₁+R₂).
Parallel: same voltage, 1/R = 1/R₁ + 1/R₂.
Primary cells (dry cell) are non-rechargeable; secondary cells (lead-acid) are rechargeable.

Worked Example

Q. A 12 V battery drives a current through a 4 Ω resistor. Find the current.

Ohm's law: I = V/R.

= 12 / 4 = 3 A.

Common traps

Reading the prompt too quickly and missing a qualifier.
Memorising the result without checking when it applies.
Skipping units, signs, chronology or the final reasonableness check.

NDA shortcuts

State the governing rule before substituting values.
Eliminate impossible options before doing full calculation.

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5 NDA questions

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Question 1

NDA Practice 2026

According to Ohm's law, the SI unit of electrical resistance is the

Question 2

NDA I 2025

If the length of a copper wire is increased by twice, then its resistivity will be

Question 3

NDA II 2024

In which one among the following situations, the bulb Ⓧ would glow the most ? (Consider all batteries are the same)

Question 4

NDA I 2024

If the current through an electrical machine running on direct current is 15 A and the machine runs for 10 minutes, the charge that passes through the machine during this time is:

Question 5

NDA II 2024

Two resistances of 5.0 Ω and 7.0 Ω are connected in series and the combination is connected in parallel with a resistance of 36.0 Ω. The equivalent resistance of the combination of three resistors is

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