Electricity — Practice

Question 1

How much charge flows when a current of 2 A passes for 5 minutes?

Accepted Answer

Step 1 — t = 5 min = 300 s.

Step 2 — Q = I × t = 2 × 300 = 600 C.

✦ Answer: 600 coulombs.

Question 2

A 12 V battery drives a current of 3 A through a resistor. Find its resistance.

Accepted Answer

Step 1 — R = V/I.

Step 2 — R = 12/3 = 4 Ω.

✦ Answer: 4 Ω.

Question 3

How should an ammeter and a voltmeter be connected in a circuit?

Accepted Answer

Ammeter in series (measures current through); voltmeter in parallel (measures voltage across).

✦ Answer: ammeter — series; voltmeter — parallel.

Question 4

Three resistors of 2 Ω, 3 Ω and 5 Ω are joined in series across a 20 V battery. Find the total resistance and the current.

Accepted Answer

Step 1 — Rₛ = 2 + 3 + 5 = 10 Ω.

Step 2 — I = V/Rₛ = 20/10 = 2 A.

✦ Answer: 10 Ω; current = 2 A (same through each).

Question 5

Two resistors of 6 Ω and 3 Ω are connected in parallel. Find the equivalent resistance.

Accepted Answer

Step 1 — 1/Rₚ = 1/6 + 1/3 = 1/6 + 2/6 = 3/6 = 1/2.

Step 2 — Rₚ = 2 Ω.

✦ Answer: 2 Ω (smaller than both resistors, as expected).

Question 6

An electric bulb is rated 220 V, 100 W. Find the current it draws and its resistance.

Accepted Answer

Step 1 — P = VI ⇒ I = P/V = 100/220 = 0.45 A.

Step 2 — R = V²/P = (220)²/100 = 48400/100 = 484 Ω.

✦ Answer: current ≈ 0.45 A; resistance = 484 Ω.

Question 7

How does the resistance of a wire change if its length is doubled and its area of cross-section is halved?

Accepted Answer

Step 1 — R = ρl/A.

Step 2 — Doubling l multiplies R by 2; halving A multiplies R by 2 again.

Step 3 — New R = 2 × 2 = 4 times the original.

✦ Answer: The resistance becomes 4 times the original.

Question 8

An electric iron of resistance 25 Ω draws a current of 4 A. Calculate the heat developed in 30 seconds.

Accepted Answer

Step 1 — H = I²Rt.

Step 2 — H = (4)² × 25 × 30 = 16 × 25 × 30.

Step 3 — H = 16 × 750 = 12000 J.

✦ Answer: 12000 J (12 kJ).

Question 9

A 1000 W heater runs for 2 hours a day. If electricity costs ₹6 per unit, find the monthly (30-day) cost.

Accepted Answer

Step 1 — Daily energy = power × time = 1 kW × 2 h = 2 kWh = 2 units.

Step 2 — Monthly energy = 2 × 30 = 60 units.

Step 3 — Cost = 60 × ₹6 = ₹360.

✦ Answer: ₹360 per month.

Question 10

A 4 Ω and a 12 Ω resistor are connected in parallel, and this combination is joined in series with a 5 Ω resistor across a 12 V battery. Find (a) the equivalent resistance and (b) the total current.

Accepted Answer

Step 1 — Parallel part: 1/Rₚ = 1/4 + 1/12 = 3/12 + 1/12 = 4/12 = 1/3 ⇒ Rₚ = 3 Ω.

Step 2 — Add the series 5 Ω: R = 3 + 5 = 8 Ω.

Step 3 — Total current I = V/R = 12/8 = 1.5 A.

✦ Answer: (a) 8 Ω, (b) 1.5 A.

Question 11

Why is series connection not used for domestic wiring? Give two reasons and state which connection is used instead.

Accepted Answer

Step 1 — In series, the same current flows and the voltage is shared, so each appliance gets less than the full 220 V and may not work properly.

Step 2 — If one appliance/bulb fails, the circuit breaks and ALL appliances stop.

Step 3 — Also, appliances cannot be switched on/off independently in series.

Step 4 — Hence homes use PARALLEL connection: each device gets full voltage, works independently, and others keep running if one fails.

✦ Answer: series shares voltage and fails together; domestic wiring uses parallel.

Practice — Electricity

Sign in to save attempts to your dashboard and track your accuracy over time

Find a verified tutor

Join a live course

Browse coaching centres

About

Categories

Support

Documentation

Get Study Tips & Updates

Download Our App

Download for iOS

Download for Android

Popular Cities