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CNMS ICSE - 7 Std
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Chapter: 05. Heat

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What is heat?
Heat is an invisible form of energy that flows from a hotter body to a colder body and causes the sensation of hotness or coldness in us.
What is the relation between a calorie and a joule?
One calorie is equal to approximately 4.186 joules.
How is temperature defined?
Temperature is the measure of the degree of hotness or coldness of a body.
Why is mercury used in liquid thermometers?
Mercury is used in thermometers because it is easily visible as a shiny thread in the capillary tube and is an excellent conductor of heat.
What is the purpose of the constriction in a clinical thermometer?
The constriction prevents the mercury level in the stem from dropping after the thermometer is removed from a patient’s mouth, allowing the temperature to be read accurately.
State the freezing point and boiling point of water on the Kelvin scale.
The freezing point of water on the Kelvin scale is 273 K and the boiling point is 373 K.
Write the mathematical formula used to convert Celsius to Fahrenheit.
The formula is C / 5 = (F - 32) / 9, where C is the temperature in Celsius and F is the temperature in Fahrenheit.
What is thermal expansion?
Thermal expansion is the increase in the volume of a substance due to heating.
Explain why a gap is left or wires are kept sagging between electric poles.
Electric wires are kept loose to allow for the contraction of the metallic wires during cold winters without snapping.
How does a bimetallic strip work when heated?
When heated, a bimetallic strip bends towards the metal strip that has the lower rate of thermal expansion.
What is the anomalous expansion of water?
The anomalous expansion of water is its unusual behavior of contracting when heated from 0°C to 4°C, and expanding only when heated above 4°C.
Define conduction.
Conduction is the process of transfer of heat in solids from a region of higher temperature to a region of lower temperature without the actual movement of its molecules.
Why do we wear woollen clothes in winter?
We wear woollen clothes because the wool and the air trapped inside its fibers are bad conductors of heat, which prevents our body heat from escaping.
Why is water considered a poor conductor of heat?
Water is a poor conductor because it does not easily transfer heat from its upper surface to its lower layers unless convection currents are allowed to form.
What is convection?
Convection is the mode of transfer of heat in a liquid or a gas by the actual movement of their molecules from the hotter parts to the colder parts.
How does a land breeze occur?
A land breeze occurs at night when the land cools faster than the sea, causing the cooler air above the land to blow towards the warmer air rising over the sea.
Define radiation.
Radiation is the process of transmission of heat in which heat energy travels directly from a hotter body to a colder body without heating the intermediate medium or requiring any material medium.
Why are light-colored clothes preferred in summer?
Light-colored clothes are preferred in summer because they are bad absorbers and good reflectors of radiant heat, keeping the body cool.
How does a thermos flask minimize heat transfer by radiation?
A thermos flask minimizes heat transfer by radiation because the inner surfaces of its double glass walls are brightly polished and silvered to reflect radiant heat.
What scientific breakthrough did Sir James Dewar achieve in 1898?
In 1898, Sir James Dewar became the first person to successfully liquefy hydrogen gas.
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