Physics · Practical apparatus

Heat-loss surface factors

Compare surface area, airflow represented by h and emissivity. Radiation uses absolute Kelvin temperature, while convection uses temperature difference. This apparatus study compares instantaneous heat-loss rates.

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Heat-loss surface factors

பரப்பு, காற்றோட்டம் மற்றும் உமிழ்திறன் வெப்ப இழப்பை மாற்றும். கதிர்வீச்சுக்கு கெல்வின் வெப்பநிலை பயன்படும்.

Key notes, relationships and model limits

Key relationship

P=hA(T−Ta)+εσA(T⁴−Ta⁴); dT/dt=−P/(mc).

Practical tip

Common trap

Radiation uses absolute temperature to the fourth power. Surface area and emissivity affect the heat-loss rate.

Model limits

instantaneous lumped convection plus grey-body radiation; conduction through supports and evaporation excluded. Negative net loss means the surroundings heat the body.

What you will learn

Adjust heat-loss surface factors apparatus, observe its reading and derive the indicated physical quantity.

Try the experiment

Try both scenarios, change one control, and predict the result before checking the graph and readouts.

Think of it this way

Change one input while keeping the others fixed, as you would in a controlled experiment.

Worked example

At 80 °C versus 25 °C, A=0.02 m² and h=10 W/(m² K), convection loss is 11 W before radiation is added.

Why this matters

The model connects heat-loss surface factors with an observable reading. Check the equation and assumptions before applying it.

Before you start

SI units · algebra · graph reading

Check your understanding

Radiation calculations must use temperatures in?

Celsius because only the temperature difference matters.
Kelvin.
Fahrenheit without conversion.

Read the explanation

Kelvin.

Course connection: Virtual apparatus preparation. Check exact board/exam membership in the syllabus sources. Physical practical work remains necessary.