Question:2. Write down Charles law with mathematical explanation.

Ans.: In 1787, Charles studied the effect of temperature on the volume of the gases at constant pressure. He formulated a relationship between volume and temperature of a gas which is known as Charles’s law. It states that, At constant pressure, the volume of a definite mass of a gas increases or decreases by part of volume at 0°C for each degree Celsius increase or decrease in temperature.

Mathematical explanation: If the volume of a given mass of a gas at constant pressure and 0°C be Vo then at t°C the volume is,

This mathematical form is called Charles law. So according to Charles law, at constant pressure, the volume of a definite mass of a gas is directly proportional to its absolute temperature.

Question:2. What is absolute zero and its scale of temperature? Or, From Charles’ law how will you get a new scale of temperature.

Ans.: Absolute zero: According to Charles’ law, at constant pressure the temperature (-273°C) at which a gas has no volume theoretically is known as absolute zero. Actually this temperature has never been reached and in fact all gases became liquid or solid before they reach such a low temperature.

According to Charles’ law at constant pressure, the volume of a definite mass of gas becomes, zero at

-273°C as shown below: If the volume of a given mass of a gas at constant pressure and 0°C be Vo then,

Thus, -273°C is the lowest possible temperature because below this temperature, the volume will become negative. This is meaningless. This lowest temperature is called absolute zero temperature.

Fig.5: Variation of volume of certain amount of gas with temp. under constant pressure conditions Absolute scale of temperature: Taking the absolute zero (i.e., -273°C) as zero, a new scale of temp., known as absolute scale of temperature, has been devised. The temperatures measured on this scale are known as absolute temperatures. The degree in the absolute scale has the same size as the centigrade degree (now known as the Celsius degree).The symbol K. that is, Kelvin, is most frequently employed in the honour of Lord Kelvin, the inventor of this scale.

Thus, temperature T on the absolute scale are obtained by adding 273°C temperatures t, viz. T = (273 +1)K

-273° C = 0K

0°C = 273 K

t°C = (273 + t) K

= TK

Therefore, T K = (273 + t) K

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