Important Points and Formulas of class 7 Science Chapter-Heat

Important Points and Formulas of class 7 Science Chapter-Heat

May 16, 2022, 16:45 IST

Class 7 Science Chapter-Heat

UNITS OF HEAT

The branch of science that deals with the measurement of heat is Calorimetry. Units used to measure heat are as follow:

• C.G. S unit: Calorie(cal)

Calorie: it is defined as heat required raising the temperature of 1 g of water through 1 degree Celsius from 14.5°C to 15.5°C

• M.K.S unit: 1 Kilo Calorie (Kcal) = 1000 Calories.
• S.I. unit: Joule (J)

The units Calorie and Joule are related as:

1 cal = 4.186 J (or nearly 4.2 J)

TEMPERATURE

Temperature is a quantity which tells the thermal state of a body (i.e., the degree of hotness or coldness of the body). It determines the direction of flow of heat when two bodies at different temperatures are placed in contact. At molecular level, when temperature increases (means body is gaining heat), we say kinetic energy of molecule increases.

THERMOMETERS AND TEMPERATURES SCALE

The sense of touch provides some indication of the temperature of an object but is unreliable. For example, the metal shelf in the refrigerator feels colder than the food sitting on the shelf, even though they are in thermal equilibrium. The metal feels colder because the metal conducts the heat from your hand more efficiently.

THERMOMETERS

Thermometers are instruments that define and measure the temperature of a system. The common thermometer consists of a volume of mercury that expands into a capillary tube when heated. When the thermometer is in thermal equilibrium with an object, the temperature can be read from the thermometer scale.

Three temperature scales are commonly used: Celsius, Fahrenheit, and Kelvin (also called absolute ). Comparisons of the Celsius and Fahrenheit thermometers are shown in Figure

A degree on Celsius is 1/100th part of the interval between the ice point and the steam point.

1 centigrade degree = 9/5 Fahrenheit degree

The relation between Fahrenheit scale and Celsius scale is

The zero of the absolute scale is the temperature at which the molecular motion ceases and the average kinetic energy of molecules becomes zero. Thus, the zero of absolute is not the ice point. Absolute zero is the lowest attainable temperature. No temperature can be less than this temperature. Therefore, this scale has no negative temperature.

T K = 273 + t°C

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Find Below Sho​rt Notes of chapter-Heat