To determine the electrical and mechanical equivalent of heat (Joule's constant J) by electrical calorimeter heating, verify Joule's law of electric power dissipation (W = V I t), and evaluate radiation cooling corrections. Explore a virtual apparatus, collect readings and analyse a graph.
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Adjust the apparatus, then take a reading.
Timing is generated from the model; a short on-screen trial represents a longer physical interval. Animation is illustrative.
Calculations assume uniform thermal mixing without fluid stagnation, negligible heat loss to the ambient environment under Rumford radiation compensation, and negligible mechanical energy added by the stirrer. Real calorimeters exhibit small convection losses governed by Newton’s law of cooling (dQ/dt = k(T − T_env)) and slight temperature lag in the thermometer bulb during rapid heating.
Provides a double-walled nickel-plated copper vessel with an insulating air jacket, phenolic lid, and internal immersion heating coil (R = 4.00 Ω) submerged in 250.0 g of distilled water with a calibrated water equivalent of 9.3 g (system heat capacity C_sys = 259.3 cal/°C).
Supplies a stable, low-ripple constant direct voltage (V = 10.00 V) and current (I = 2.500 A) to deliver a steady electrical dissipation power P = 25.00 W throughout each heating interval.
Monitors the potential difference across the immersion coil (10.00 V ± 0.01 V) and loop current (2.500 A ± 0.002 A) to continuously measure electrical work W = V · I · t with high precision.
Measures water temperature from 15.00 °C to 45.00 °C with 0.02 °C resolution, immersed at the geometric center of the stirred water volume.
Circulates the water volume gently and continuously to eliminate localized hot spots around the heating coil without adding appreciable mechanical frictional heat.
Times the duration of electrical current flow with 0.01 s precision from 120.0 s to 720.0 s for exact energy computation.
To determine the electrical and mechanical equivalent of heat (Joule's constant J) by electrical calorimeter heating, verify Joule's law of electric power dissipation (W = V I t), and evaluate radiation cooling corrections. Suggested independent settings: 120.0, 240.0, 360.0, 480.0, 600.0, 720.0 s.
Weigh the clean, dry inner copper calorimeter vessel on a balance, add exactly 250.0 g of distilled water, and re-weigh to verify total mass. Place the inner vessel inside the outer insulating air jacket, seat the phenolic lid, and insert the immersion heating coil, motorized stirrer, and fractional-degree thermometer.
Accurate initial water mass is required to compute the baseline system heat capacity C_sys = m_w c_w + W_eq.
Activate the motorized stirrer at gentle speed and allow the calorimeter system 5 minutes to reach thermal equilibrium with the ambient laboratory. Read and record the initial quiescent temperature T₀ = 20.00 °C on the fractional-degree thermometer.
Starting from stable ambient room temperature minimizes initial convective heat exchange before electrical energy is introduced.
Connect the regulated DC power supply in series with the ammeter and immersion heating coil. Connect the digital voltmeter directly across the coil terminal posts (four-wire Kelvin sensing) to exclude lead resistance drops. Energize the supply momentarily to set V = 10.00 V and I = 2.500 A (P = 25.00 W), then open the main switch.
Kelvin voltage sensing across the coil terminals ensures that only the electrical power dissipated inside the water is integrated into the work calculation.
Simultaneously close the power switch and start the digital chronometer. Maintain continuous gentle stirring while monitoring the voltmeter and ammeter to verify constant power delivery. Run the heating for an initial duration of 120.0 s (2.0 min, delivering W = 3000 J), open the switch, and continue stirring until the thermometer reaches its maximum stabilized reading T.
Stirring after switching off ensures that all thermal energy stored in the heating wire sheath diffuses into the water before reading peak temperature.
Repeat the timed heating runs for cumulative durations of 240.0 s (6000 J), 360.0 s (9000 J), 480.0 s (12000 J), 600.0 s (15000 J), and 720.0 s (18000 J), recording the peak stabilized temperature T at each duration. Compute the temperature rise ΔT = T − T₀ and the corresponding heat absorbed Q = C_sys · ΔT in calories.
Sampling six evenly spaced durations spanning 3000 J to 18000 J provides wide leverage for linear regression analysis.
Plot heat absorbed Q (in calories) on the horizontal axis and electrical energy W = V · I · t (in Joules) on the vertical axis. Compute ordinary least-squares linear regression to determine the slope J = ΔW / ΔQ (in J/cal) and the vertical intercept b. Calculate the heat equivalent of electrical energy a = 1 / J (in cal/J) and compare against standard reference values.
Linear regression averages out thermometer quantization and minor radiation losses, isolating the pure conversion factor between electrical work and thermal energy.
Points are your observations. The fit uses SI x and y values before display scaling.
| # | Heating duration t (s) | Calorimeter temperature T (°C) | Heat absorbed Q (cal) | Electrical energy W (J) | Remove |
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