E-Lecture - Important Points
- Heat is defined as a form of energy in transit due to temperature differences. it is therefore measured in joules (J).
- The temperature of a substance is a measure of the average kinetic energy of the particles within the substance. Temperature is a fundamental physical quantity whose SI unit is Kelvin (K).
- Two objects are said to be in thermal equilibrium if they have the same temperatures. Two objects in thermal equilibrium do not exchange heat energy.
- The most commonly known scales which scientists now tend to deal with are the Kelvin scale (K), the Celsius scale (°C) and the Fahrenheit scale (°F).
- Thermometry is the process of measuring temperature of substances. The instrument that is used to measure temperature is known as Thermometer.
- Anybody with at least one measurable property that changes with temperature can be used as thermometer. Such a property is called thermometric property.
- The particular substance that exhibits changes in the thermometric property is known as thermometric substance.
- One of the effects of heating is thermal expansion. Substances expand when they absorb heat and contract when they release heat. Thermal expansion or contraction occurs spherically in all dimensions but it can be broken down into three categories: Linear expansion, surface (area) expansion and volume expansion.
- The change in length ∆L of a substance, attained by heating, is directly proportional to the product of the original length Lo, and the change in temperature ∆T. Thus, ∆L= α L0 ∆T, where the proportionality constant ais called the coefficient of linear expansion.
- The change in area of a substance is ∆A = βA0 ∆T, where the proportionality constant γ is called the coefficient of area expansion.
- The change in volume of a substance is ∆V = γV0 ∆T, where the proportionality constant γ is called the coefficient of volume expansion.
- The coefficients of expansion constants are related as γ = 3α, β = 2α
- Boyle’s law states that when the gas is kept at a constant temperature, its pressure P is inversely proportional to its volume,
- Charles’ law states that when the pressure is kept constant, the volume of the gas is directly proportional to its temperature,
- According to the pressure law, when the volume is constant, the pressure is directly proportional to the temperature,
- The general gas law can be described as when all the three parameters are changing, then the product of pressure and volume is directly proportional to the temperature.
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