PASCO Experiment: How Colour Affects Heat Absorption

Aim

Measure and compare the rate and magnitude of temperature rise in liquids with different surface colours under the same illumination.

Big ideas (GCSE/A-Level links)

• Energy transfer by radiation; absorption vs reflection

• Specific heat capacity (controlled)

• Experimental design: variables, repeats, averages

• Data handling: gradient as a rate, curve comparison

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Equipment

• PASCO Wireless Temperature Sensors (PS-3201) × 3–5

• Optional: PASCO Wireless Light Sensor (PS-3213) or Weather/Light Meter (to log incident light)

• SPARKvue (iPad/Chromebook/PC) or PASCO Capstone

• Identical clear containers (100–250 mL beakers or PET cups) × number of colours

• Food dye (blue, red, black) or coloured card/film wraps (matte black, white, red, blue, silver)

• Water (same volume & start temp for all)

• Light source: full-spectrum LED panel or halogen lamp at fixed distance (or direct sun; see controls)

• Ruler/tape (to fix lamp distance), tripod/stands and sensor clamps

• Thermal/reflective mat (to reduce conduction from bench), stopwatch

• Safety: heat-resistant gloves for halogen lamps; cable management

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Variables

• Independent: Colour (of liquid or container surface)

• Dependent: Temperature (°C) vs time; optionally incident light (lux)

• Controls: Water volume, initial temperature, container shape/size, lamp distance/angle, exposure time, room airflow

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Preparation & Calibration (5–8 min)

1. Label containers: Black, White, Red, Blue, Silver (or Dyed Black/Blue/Red + Clear Control).

2. Equal volumes: 150 mL water each. Let all equilibrate to room temperature (±0.5 °C).

3. Sensor check:

   • Open SPARKvue → Add Sensor → connect all temp sensors; rename them by colour.

   • If using a Light Sensor: connect and zero in the experiment position without the lamp on; then start a 10-s baseline.

4. Geometry: Place containers on an insulating mat, in a straight line perpendicular to the lamp, with front faces aligned. Set lamp at a fixed distance (e.g., 40 cm) and height so each container is illuminated equally. Use a bookend/board behind to block backlight spill.

Tip: If using sunlight, run all colours simultaneously; log global illumination with the Light Sensor and note any cloud events. Avoid drafts.

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Method (student-friendly steps)

A. Baseline (2 min)

1. Insert each temperature probe mid-depth, not touching sides/bottom.

2. Start recording in SPARKvue (1 Hz sampling).

3. Log 60 seconds with the lamp OFF to capture starting temperatures.

B. Exposure (10–15 min)

4. Switch the lamp ON. Start a countdown timer (10 minutes typical).

5. Do not stir. Keep room conditions stable.

6. Watch the live graph; ensure no sensor has drifted or touched a wall. If necessary, pause and correct, then note the interruption time in your log.

C. Cooling (optional, 5–10 min)

7. Turn the lamp OFF and continue logging while samples cool to observe cooling curves (useful for modelling).

D. Replicates

8. Repeat the run at least twice (swap container positions between runs to remove positional bias).

9. For dyed-water version, ensure dye concentrations are consistent (e.g., 4 drops per 150 mL).

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Data capture settings (suggested)

• Sampling rate: 1 sample/s (higher gives noisier curves without benefit).

• Display Table + Graph (T vs t for each colour).

• If using Light Sensor: add lux vs t panel; keep within the lamp’s stable output.

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Analysis

1) Initial heating rate (gradient)

• In SPARKvue, use the slope tool over the first 180 s for each curve.

• Record dT/dt (°C·s⁻¹) → this is your absorption rate proxy.

2) Peak temperature

• Read T_max after fixed exposure time (e.g., 10 min).

3) Area under curve (optional)

• Integrate T(t) above baseline to compare total thermal gain.

4) Statistics

• Compute mean ± SD for dT/dt and T_max across replicates.

• Bar chart T_max and dT/dt by colour with error bars.

• If using sunlight, normalise by average lux during each run.

Expected trend

• Black (or very dark) absorbs the most → steepest slope, highest T_max.

• White/Silver reflect more → shallowest slope, lowest T_max.

• Blue/Red sit between, depending on lamp spectrum and dye absorbance.

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Example results table (template)

Colour	Run	dT/dt (°C·min⁻¹)	T_max (°C)	ΔT @10 min (°C)
Black	1	1.9	37.6	18.3
Black	2	2.0	37.9	18.7
White	1	0.9	31.2	11.9
White	2	1.0	31.4	12.1
…	…	…	…	…

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Validity & controls

• Position swap between runs to cancel hot-spot effects.

• Same volume & start temp for all samples.

• Matte surfaces absorb more consistently than glossy (specify finish).

• Avoid convection drafts (close doors/vents).

• Keep lamp output constant; warm-up LEDs/halogen for 2–3 min before baseline.

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Safety

• Lamps and housings can become hot; handle with care.

• Manage trip hazards from power leads.

• Use low-voltage LED if possible; if halogen, keep combustibles clear.

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Extensions (great for A-Level projects)

• Spectral angle: Add coloured filters between lamp and sample; discuss wavelength-dependent absorption.

• Surface vs volume: Compare coloured wraps on containers (surface effect) vs dyed liquids (volumetric absorption).

• Material albedo: Replace water with sand/soil trays wrapped in different colours (links to urban heat island).

• Model fitting: Fit heating curves to Newtonian heating with an added source term; estimate effective absorptivity constants.

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Conclusion prompt (for students)

• Rank colours by heating rate and peak temperature.

• Explain differences using absorption/reflection and electromagnetic spectrum.

• Evaluate uncertainties and improvements for future runs.

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How we teach this at Hemel Private Tuition

At Philip M Russell Ltd (Hemel Private Tuition) we run this practical live in our lab or through our multi-camera online studio so students see the curves build in real time in SPARKvue/Capstone. We pair it with discussion of radiation physics, experimental design, and data analysis skills needed for GCSE and A-Level success.