The energy that is being transferred between two bodies or between adjacent parts of a body
as a result of temperature difference is called heat. Thus, heat is a form of energy. It is energy
in transit whenever temperature differences exist. Once it is transferred, it becomes the internal
energy of the receiving body. It should be clearly understood that the word "heat" is meaningful
only as long as the energy is being transferred. Thus, expressions like "heat in a body" or
"heat of a body" are meaningless
In early days heat was not recognized as a form of energy. Heat was supposed
to be something needed to raise the temperature of a body or to change its
phase. Calorie was defined as the unit of heat. A number of experiments were
performed to show that the temperature may also be increased by doing
mechanical work on the system.
Specific heat of substance is equal to heat gain or released by that substance to raise or fall
its temperature by 1ºC for a unit mass of substance.
Heat capacity of a body is defined as the amount of heat required to raise the temperature
of that body by 1°. If 'm' is the mass and 's' the specific heat of the body, then
Heat capacity = m s.
It is the amount of water which requires the same amount of heat for the same temperature rise as
that of the object
The branch of thermodynamics which deals with the measurement of heat is
Zeroth law of thermodynamics
Most materials expand when their temperature is increased. Rails roads
tracks, bridges all have some means of compensating for thermal expansion.
When a homogeneous object expands, the distance between any two points
on the object increases. Figure shows a block of metal with a hole in it
When the rod is heated, its increase in length ?L is proportional to its original
If the rod is free to expand then there will be no stress and strain. Stress and strain is
produced only when an object is restricted to expand or contract according to change in
temperature. When the temperature of the rod is decreased or increased under constrained
condition , compressive or tensile stresses are developed in the rod. These stresses are
known as thermal stresses.
The time represented by the clock hands of a pendulum clock depends on the number
of oscillation performed by pendulum every time it reaches to its extreme position the
second hand of the clock advances by one second that means second hand moves by
two seconds when one oscillation in complete
Measurement of length by metallic scale
When a solid is heated and its area increases, then the thermal
expansion is called superficial or areal expansion. Consider a solid plate
When a solid is heated and its volume increases, then the expansion is
called volume expansion or cubical expansion. Let us consider a solid or
liquid whose original volume
VARIATION OF DENSITY WITH TEMPERATURE
As we known that mass = volume × density .
Mass of substance does not change with change in temperature so with increase of
temperature, volume increases so density decreases and vice-versa.
APPARENT EXPANSION OF A LIQUID IN A CONTAINER
VARIATION OF FORCE OF BUOYANCY WITH TEMPERATURE
It two strip of different metals are welded together to form a bimetallic strip, when heated uniformly it bends in
form of an arc, the metal with greater coefficient of linear expansion lies on convex side. The radius of arc thus
formed by bimetal is
Temperature may be defined as the degree of hotness or coldness of a body. Heat energy
flows from a body at higher temperature to that at lower temperature until their temperatures
become equal. At this stage, the bodies are said to be in thermal equilibrium.
Thermometers are device that are used to measure temperatures. All thermometers are based on the
principle that some physical property of a system changes as the system temperature changes.
Required properties of good thermometric substance.