Page 35 - Ripples SCIENCE 7 - TEJPUR Edition 2024 Answer Key

4. Heat and Temperature

Chapter in a Nutshell

v The form of energy that is transferred between two substances at different temperatures is
called heat.
v Temperature gives us an exact measure of the degree of hotness or coldness of a body. It is

measured by a device called thermometer.
v Thermometer works on the principle of thermal expansion which states that matter expands

on cooling and expands on heating.
v Thermometer uses mercury as fluid to measure temperature.

v Clinical thermometer is used to measure human body temperature.
v The normal body temperature of a healthy human is 37°C or 98.6°F.

v A laboratory thermometer is used to measure the temperature of substances other than
human beings.
v A maximum-minimum thermometer is used to measure the maximum and minimum

temperatures of a day. It is used in forecasting the weather.
v Nowadays digital thermometers are used instead of clinical thermometers. They display the

correct temperature on a display screen.
v Three types of scales are used for measuring temperature–Celsius scale, Fahrenheit scale
and Kelvin scale and three units of temperature – degree Celsius (°C), degree Fahrenheit (°F)

and Kelvin (K).
v The lower and upper fixed points on the Celsius scale are 0°C (freezing point of pure water)

and 100°C (boiling point of pure water).
v The lower and upper fixed points on the Fahrenheit scale are 32°F (melting point of pure

water) and 212°F (boiling point of pure water).
v The lower and upper fixed points on the Kelvin scales are 0 K and 273 K respectively.

v We can convert temperatures of one scale to the other by using the following formulae:

=
(a) °C (°F – 32) (b) K = °C + 273
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v The transfer of heat always takes place from the hotter object (object at high temperature) to
the colder object (object at a lower temperature). This transfer of heat continues until both

the objects have reached the same temperature. This temperature is known as equilibrium
temperature.
v There are three methods of heat transfer—conduction, convection and radiation.

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