Thermodynamics & Energy · GCSE Physics Topic 3
Thermal Expansion & Bimetallic Strip Thermostat Simulator
Key exam takeaway: Heating bends the strip toward the metal with the SMALLER expansion coefficient. Cooling bends it toward the metal with the LARGER coefficient.
- Client-side
- No Sign-up
- Live Derivation
- Projector Mode
- Print Worksheet
3D Simulation Stage● 60 FPS
Parameter Controls
°C
×10⁻⁶/K
×10⁻⁶/K
mm
Live Derivations & Metrics
Tip Deflection δ
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Contact Switch State
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Curvature Radius R
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Bending Orientation
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Real-Time Formula Derivation
Governing Formula:
--Substitution:
--Regime: --
Worked Examples & Exam Question Deep Dive
Worked Problem
Problem: A 100m steel rail laid at -10°C faces 40°C in summer (α = 1.2*10^-5 /°C). Find thermal expansion stretch and joint gap.
Step-by-Step Derivation:
- Δt = 50°C. Stretch ΔL = α * L * Δt = 1.2*10^-5 * 100 * 50 = 0.06m = 6cm. Joint gap must exceed 6cm.
Worked Problem
Problem: A bimetallic strip is made of copper and iron (copper expands more). Which way does it bend when heated? When cooled?
Step-by-Step Derivation:
- Heated: bends toward the iron side (iron on concave inside). Cooled: bends toward the copper side (copper contracts more).
Student Inquiry Worksheet & Practice Problems
Q1. Variant 1: What principle governs liquid thermometers? Why can't water be used as thermometric fluid?
Answer Key: Based on thermal expansion. Water exhibits anomalous expansion (contracts between 0°C and 4°C), causing false inverted readings.
Q2. Variant 2: Why do long steam pipelines feature periodic Ω-shaped (horseshoe) expansion loops?
Answer Key: Expansion compensators! They flex elastically to absorb longitudinal thermal expansion strain, preventing pipe rupture.
Q3. Variant 3: Why do power lines sag in summer and tighten in winter? What caution must linemen exercise when stringing in summer?
Answer Key: Summer heat stretches wires; winter cold contracts them. Linemen must allow sufficient slack in summer to prevent winter snaps.
Frequently Asked Questions & Misconceptions
Why is water's maximum density at 4°C vital for freshwater fish winter survival?
4°C dense water sinks to the lake bottom while 0°C ice floats on top as an insulating blanket, keeping the lake bottom stably at 4°C.
Why are asphalt expansion relief joints cut into concrete highways every dozen meters?
Prevents road buckling! Without expansion slits, intense summer solar heat expands concrete until slabs buckle violently and shatter.
How do fire alarms and MEMS devices implement bimetallic strips?
Ambient fire heat curls the bimetallic beam across a contact gap, triggering alarm sirens; in MEMS, differential expansion tilts micro-mirrors.
If a steel ruler calibrated at 0°C is used in a 40°C heatwave, does the reading err high or low?
Reads LOW! The steel ruler thermally expands, spacing millimeter marks further apart, so fewer units span the measured object.