Page 39 - Science Class 07

Convection : Transfer of heat from one portion of a liquid or gas to another portion
Radiation : Transfer of heat without any medium
Conductor : An object which can allow heat to pass through it

Insulator : An object which can not allow heat to pass through it

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i Heat can be transferred from one body to another body having temperature difference.
i When water is heated its molecules starts moving because heat energy is converted into
kinetic energy.
i The French scientist Jacques Charles discovered that heat could be transformed into motion.
i Sir James Prescott Joule, a 19th century Physicist later proved that a given amount of
mechanical energy always produces the same amount of heat.

i The three scales to measure temperature are — the Celsius scale, the Fahrenheit scale and
the Kelvin scale.
i Some important kind of thermometers are— Liquid-in-glass-thermometer, clinical
thermometer, thermometer for industry and resistance thermometer.
i Radiation can take place in vacuum as well as in air.

i Thermos Flask is a device designed to prevent loss of heat through conduction and
convection as well as through radiation.

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A. Tick (3) the correct op on.
1. Who discovered that heat could be transformed into mo on?
(a) James Wa (b) Issac Newton

(c) Jacques Charles (d) James Presco Joule
2. Which of the following is not a scale of temperature measurement?
(a) Celsius (b) Fharenheit
(c) Kelvin (d) Lumen
3. Which of the following materials is used in clinical thermometer?

(a) Iodine (b) Mercury
(c) Radium (d) None of these
4. Sun rays heat up the earth’s surface through the process of:

(a) conduc on (b) radia on
(c) convenc on (d) none of these
5. Which of the following materials is an insulator?
(a) Iron (b) Silver

(c) Wood (d) Water

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