Home » Handbook of O Level Physics » UNIT 8: MEASUREMENT OF TEMPERATURE

UNIT 8: MEASUREMENT OF TEMPERATURE

• Temperature: It is a measure of the average kinetic energy of the atoms or molecules in a body. (It tells us how hot or cold something is.)

• Heat: Heat is the energy that is exchanged between two objects due to their difference in temperature.

• Calibrating a thermometer:

• Step 1: To measure temperature we need a physical quantity that is affected by temperature. For example volume, e.m.f., resistance or pressure.

• Step 2: Mark 0oC (using pure melting ice) and 100oC (by placing just above boiling water).

• Step 3: Divide the temperature range between the two marks into 100 equal parts.

• Thermometric liquids:

Mercury

Alcohol

• Good conductor

• Does not wet glass

• High boiling point

• Not poisonous

• Cheap

• Low freezing point

• Poisonous

• Expensive

• High freezing point (-39oC)

• Wets glass

• Low boiling point (78oC)

• Some definitions:

• Responsiveness: It is about how quickly you get the result.

• Sensitivity: It is about how much does the thermometric property (e.g., volume) change per degree change in temperature.

• Range: The minimum and maximum temperatures that can be measured.

• Linearity: It is about whether each degree is an equal distance or not.

• Liquid-in-glass thermometers: In comparison to a laboratory thermometer, a clinical thermometer has:

• a constriction

• less range

• greater sensitivity (divisions further apart)

• triangular cross-section (for magnification)

• Thermocouple thermometers:

• Construction: You should be able to draw figure 8.13.

• Defining equation: e.m.f. = Δ θ