Bright Tutorials Bright Tutorials
CBSE Class 10 Science Question 2 of 18

Electricity — Question 3

Back to all questions
3
Question

Question 3

An electric bulb is rated 220 V and 100 W. When it is operated on 110 V, the power consumed will be ...............

  1. 100 W
  2. 75 W
  3. 50 W
  4. 25 W
Answer

25 W

Reason —

Given, V = 220V ; P = 100 W ; R = ?

We know,

⇒P=V2R⇒R=V2P\phantom{\Rightarrow} \text{P} = \dfrac{\text{V}^2}{\text{R}} \\[1em] \Rightarrow \text{R} = \dfrac{\text{V}^2}{\text{P}}

Substituting the values, we get

R = 2202100\dfrac{\text{220}^2}{\text{100}} = 484 Ω

When voltage is reduced, resistance remains the same. Hence, the power consumed :

P = 1102484\dfrac{110^2}{484} = 25 W

Hence, the power consumed = 25 W.

Web Content: Electricity | Bright Tutorials
BRIGHT TUTORIALS
Bright Tutorials Logo
BRIGHT TUTORIALS
CBSE Class X | Academic Year 2026-2027
9403781999
Excellence in Education
Science | Chapter 11: ElectricityWeb Content

Chapter 11: Electricity — Quick Revision Guide

Introduction

Electricity powers modern life. This chapter covers electric current, potential difference, Ohm's law, resistance, series and parallel circuits, and electrical power and energy calculations.

Key Points at a Glance

  1. Current I = Q/t (ampere); potential difference V = W/Q (volt); Ohm's law V = IR
  2. Resistance R = V/I (ohm); factors: R ∝ l, R ∝ 1/A, material (ρ), temperature; R = ρl/A
  3. Conductors: low ρ (~10−8 Ω·m); alloys: higher ρ, used in heating elements (nichrome)
  4. Series: Req = R1 + R2 + ...; same current; voltage divides; one failure breaks all
  5. Parallel: 1/Req = 1/R1 + 1/R2 + ...; same voltage; current divides; independent operation; used in homes
  6. Power: P = VI = I2R = V2/R (watt); Energy: E = Pt (joule); 1 kWh = 3.6 × 106 J
  7. Heating effect: H = I2Rt; applications: heater, iron, fuse (low m.p. alloy, series with live wire)
  8. Electric bill: units (kWh) = power(kW) × time(h); cost = units × rate

Real-World Connections

Household wiring in parallel allows independent appliance use; fuses and MCBs prevent fire; LED bulbs save energy (lower power for same brightness); electricity bill management.

Quick Self-Test (5 Questions)

  1. What is the most important concept you learned from this chapter?
  2. Can you write three key equations/formulae from this chapter from memory?
  3. Draw a labelled diagram relevant to this chapter without looking at your notes.
  4. Explain one real-world application of a concept from this chapter.
  5. What is one common mistake students make in this chapter, and how can you avoid it?

Further Study

  • NCERT Textbook Chapter 11
  • NCERT Exemplar Problems
  • Bright Tutorials Detailed Notes: ch11-electricity.html
  • Bright Tutorials Practice Questions: ch11-electricity.html
  • Previous Year CBSE Board Papers

Bright Tutorials | Hariom Nagar, Nashik Road | 9403781999 | brighttutorials.in