Doppler Effect This effect, where there is a change in
frequency and wavelength, is called the
It is named after the Austrian physicist Doppler Effect.
Christian Doppler, who proposed it in When a source moves towards an
1842 in Prague. observer, the observed wavelength
You may have noticed that when an decreases and the frequency increases.
ambulance or police car goes past, its siren When a source moves away from an
is high-pitched as it comes towards you, observer, the observed wavelength
then becomes low-pitched as it goes away. increases and the frequency decreases.
HEAT & TEMPERATURE
Heat Body temperature can rise to 105 degrees
if working outside in a heat wave. Death
It is a form of energy and measures the occurs usually when a body temperature
total energy of all molecules in the reaches 107.6.
You’ll lose weight in the heat.
It is a total kinetic energy of all molecules
in a substance. The average temperature on Mars is -63C.
Its units are Calorie (cal), Kilocalorie Good heat conductors: Gold, Copper,
(kcal) or Joule (J). Its CGS unit is the erg Silver, Iron, Aluminum, Nickel, Zinc &
= 10-7 joule. most other metals
1 cal = 4.18 joule Bad heat conductors: Plastic, Bakelite,
1 kcal = 1000 cal Styrofoam, Air, Water, Rubber, Cotton,
Silk, Marble, Wood, Mica
When lightning strikes it can reach up to
It is a measure of degree of hotness or 30,000 degrees Celsius (54,000 degrees
coldness of a body. Fahrenheit)
The unit of degree Celsius or Kelvin or Room temperature is defined as between
degree Fahrenheit. 20° to 25°C (68° to 77°F)
Two bodies cannot be in thermal When water freezes it expands by 9%
equilibrium if they are at different
Hot water freezes quicker than cold water
It is a measure of average kinetic energy Normal body temperature is 37°C (99°F)
of molecules in a substance. The center of the Sun is approximately 15
The formula relating all temperature scales million°C
C F 32 R K
5 9 4 5 It is an instrument for measuring
Facts about Heat and Temperature Optical pyrometer : It determines the
temperature of a very hot object by the
The highest temperature ever recorded on color of the visible light it gives off.
Earth was 136 Fahrenheit (58 Celsius) in Radiation pyrometer : It determines the
the Libyan desert. The coldest temperature temperature of an object from the radiation
ever measured was -126 Fahrenheit (-88 (infrared and, if present, visible light)
Celsius) at Vostok Station in Antarctica. given off by the object.