Electricity & Magnetism · GCSE Physics Topic 4 (Electricity & Power)
Rated vs Actual Power Bulb Brightness Simulator
Key exam takeaway: Bulb brightness depends solely on ACTUAL power dissipation. In series, the 40W bulb has higher resistance (R=U²/P) and glows brighter than the 100W bulb.
- Client-side
- No Sign-up
- Live Derivation
- Projector Mode
- Print Worksheet
3D Simulation Stage● 60 FPS
Parameter Controls
V
W
W
Live Derivations & Metrics
Bulb 1 Actual Power
--
Bulb 2 Actual Power
--
Bulb 1 Resistance R1
--
Bulb 2 Resistance R2
--
Real-Time Formula Derivation
Governing Formula:
--Substitution:
--Regime: --
Worked Examples & Exam Question Deep Dive
Worked Problem
Problem: Bulbs L1 (6V 3W) and L2 (6V 6W) wired in series across 9V. Which lights normally? Does either burn out?
Step-by-Step Derivation:
- I1_rated = 0.5A, R1 = 12Ω. I2_rated = 1.0A, R2 = 6Ω. Series current I = 9/(12+6) = 0.5A. L1 operates at rated 0.5A normally; L2 operates dimly; neither burns.
Worked Problem
Problem: An electric meter reads 3000 rev/(kW·h). A kettle alone turns disk 150 rev in 3 min. Find its actual electrical power.
Step-by-Step Derivation:
- Energy consumed W = 150/3000 = 0.05 kW·h = 180 kJ. Time t = 180s. Actual power P = W/t = 180,000/180 = 1000W.
Student Inquiry Worksheet & Practice Problems
Q1. Variant 1: Comparing 220V 40W and 220V 100W incandescent bulbs, which filament is thicker?
Answer Key: From R = U²/P, higher power requires lower resistance. The 100W bulb has lower resistance and a thicker, shorter tungsten filament.
Q2. Variant 2: In measuring bulb power, can multiple trial wattages be averaged as "rated power"? Why?
Answer Key: Never! Actual power varies with voltage. Rated power is defined strictly at rated voltage. Averaging different voltage trials is physically meaningless.
Q3. Variant 3: Why do incandescent lightbulbs almost always burn out the instant they are switched on?
Answer Key: Cold tungsten has 10x lower resistance than at operating temperature. Turning it on creates a massive 10x current surge that blows weak spots.
Frequently Asked Questions & Misconceptions
Is "kWh" a unit of power or energy? How many Joules is 1 kWh?
Energy! 1 kWh = 1000W * 3600s = 3.6*10^6 Joules (3.6 MJ). It powers a 100W bulb for 10 hours.
Why are LED bulbs far more energy-efficient than incandescent bulbs?
Incandescent bulbs waste >90% of electricity as invisible thermal infrared heat. LEDs generate light via solid-state electroluminescence at >50% efficiency.
To connect two 110V bulbs in series across 220V, what condition must hold?
Their rated wattages must be strictly identical! Otherwise unequal resistances split voltage unequally, overvolting and blowing the higher-resistance bulb.
Do household appliances consume power in standby mode?
Yes! Internal power transformers and microcontrollers remain energized, drawing 0.5W to 5W per device continuously (phantom load).