Q: What does Specific Heat Capacity: Electrical vs Mixing Methods for A-Level Physics cover? A: Compare electrical heating and mixing methods for measuring specific heat capacity.
TL;DR Two paths to the same answer: zap metal blocks with heaters or mix hot and cold water. This guide compares both methods for measuring specific heat capacity, shows how to correct for heat losses graphically, and explains why electrical heating typically gives better results. Master these techniques for full marks in thermal physics practicals.
Why Specific Heat Capacity Matters
Specific heat capacity c tells us how much energy is needed to warm something up:
Q=mcΔT
Where:
Q = Energy transferred (J)
m
= Mass (kg)
c = Specific heat capacity (J kg⁻¹ K⁻¹)
ΔT = Temperature change (K)
But measuring c accurately is tricky - heat loves to escape, and your 4186 J kg⁻¹ K⁻¹ for water might come out as 3800 if you're not careful.
Method 1: Electrical Heating
The Setup
Equipment needed:
Metal block (aluminum/copper) with holes
Immersion heater (12V, 50W typical)
Thermometer or temperature probe
Power supply with ammeter/voltmeter
Stopwatch
Insulation (polystyrene/foam)
Assembly:
Insert heater in one hole
Thermometer in other hole
Add oil drops for thermal contact
Wrap block in insulation
Connect power supply
Experimental Procedure
Record initial temperatureT0
Switch on heater at known power
Record temperature every 30s for 10 minutes
Continue recording after heater off for 5 minutes
Measure voltage V and current I regularly
Calculating Heat Capacity
Energy supplied: Q=VIt
From Q=mcΔT:
c=mΔTVIt
Example calculation:
Aluminum block: m=1.00 kg
Heating: V=12.0 V, I=4.00 A, t=300 s
Temperature rise: ΔT=16.0 K
c=1.00×16.012.0×4.00×300=900 J kg−1 K−1
(Actual value for aluminum: 897 J kg⁻¹ K⁻¹)
Advantages of Electrical Method
✓ Precise energy measurement (±1%) ✓ Continuous temperature monitoring ✓ Works for solids and liquids ✓ Easy to repeat and average
Common Sources of Error
Heat losses to surroundings (biggest issue)
Heater not fully immersed
Poor thermal contact (air gaps)
Power fluctuations
Temperature probe lag
Method 2: Mixing Method
The Classic Approach
Equipment needed:
Calorimeter (polystyrene cup works)
Hot water supply
Cold water
Thermometer
Balance (±0.1g)
Stirrer
Experimental Procedure
Measure mass of calorimetermcal
Add cold water, measure mass mcold
Record initial temperatureTcold
Heat separate water to ~60°C
Quickly add hot water, stir rapidly
Record maximum temperatureTfinal
Measure total mass for mhot
The Energy Balance
Heat lost by hot water = Heat gained by cold water + calorimeter
Dulong-Petit law: Molar heat capacity ≈ 3R for solids
Energy Conservation
Both methods demonstrate:
Energy cannot be created/destroyed
All energy transfers accounted for
Losses explain discrepancies
Your Success Strategy
✓ Choose method wisely based on material ✓ Minimize heat losses with good insulation ✓ Apply cooling corrections graphically ✓ Calculate uncertainties throughout ✓ Compare with data book values ✓ Explain discrepancies scientifically ✓ Show all working clearly ✓ Link to thermal physics principles
Master both methods and you'll handle any heat capacity question confidently. You'll understand why your car engine needs coolant, why water moderates climate, and why metals feel colder than wood - all from measuring how much energy it takes to warm things up.
Specific Heat Capacity: Electrical vs Mixing Methods for A-Level Physics
