Thermal Properties of Matter — Class 11 Physics

Temperature is a measure of the hotness of a body, and heat is energy transferred between a body and its surroundings because of a temperature difference. Temperature is measured on the Celsius, Fahrenheit and absolute (Kelvin) scales, related by and ; the ideal-gas equation defines absolute temperature, with absolute zero at C. Most substances expand on heating, characterised by coefficients of linear, area and volume expansion with ; water shows anomalous expansion near 4 degrees Celsius. Specific heat capacity is the heat needed to raise unit mass by one degree, and molar specific heat refers to one mole; calorimetry uses the principle that heat lost equals heat gained. During a change of state — melting, vaporisation — temperature stays constant and the heat absorbed is the latent heat. Heat is transferred by conduction (through ), convection and radiation. A black body absorbs all radiation; Stefan's law gives the radiated power as proportional to , Wien's law gives the wavelength of peak emission, and the greenhouse effect warms the Earth. Newton's law of cooling states that the rate of cooling is proportional to the temperature difference with the surroundings.