Class 9 science question answer of chapter number 1 part 3

Class 9 science question answer of chapter number 1  part 3

Question 1:Convert the following temperature to Celsius scale

(a) 300 K (b) 573 K 

Solution: By the use of given formula, we can convert the Kelvin 

temperature to Celsius.

T K –273 = t°C

(a) 300K–273 = 27°C

(b) 573K–273 = 300°C

Question 2:What is the physical state of water at 

(a) 250°C (b) 100°C?

Solution:As the boiling point of water is 100°C so(a) at 250°C, the state of water will be steam or water vapour, i.e., gaseous state. (b) at 100°C, there will be a transition of liquid state into the gaseous state. So, at this temperature, the state is/may be liquid as well as gaseous. 

Question 3:For any substance, why does the temperature remain constant during the change of state?


Solution:During the change of state of a substance, the temperature remains constant. This can be understood with the help of an example. When a solid is heated to its melting point, the temperature first rises and becomes constant when reaches its melting point. Now, on further heating, the heat energy provided to the substance helps to break the attraction force between the solid molecules. This heat is called latent heat. That is why, the temperature does not rise.

Question 4:Suggest a method to liquefy atmospheric gases.Solution:By applying pressure and reducing the temperature, atmospheric gases can be liquefied

Question 1:Why does a desert cooler cool better on a hot dry day?

Solution:A desert cooler functions on the basis of evaporation. The rate of evaporation increases with increase in temperature and decrease in humidity. As evaporation increases when the day is hot and dry. So, the desert cooler functions to a better extent.

Question 2:How does the water kept in an earthen pot (matka) become cool during summer?

Solution: Large number of tiny pores is present on the surface of the earthen pot (matka). The water stored in the earthen pot (matka) evaporates faster through these pores due to the increased exposed surface area. As the' process of evaporation causes cooling, the stored water inside the earthen pot (matka) becomes cool.

Question 3:Why does our palm feel cold when we put some acetone or petrol or perfume on it?

Solution:Acetone, petrol, perfume etc., being volatile, evaporate very 

fast when exposed to larger surfaces. During the process they absorb 

the required latent heat of vaporization from the palm (if kept on palm). So, the process causes Cooling and the palm feels cool.


Question 4:Why are we able to sip hot tea or milk faster from a saucer rather than a cup?

Solution: A liquid has large surface area in a saucer than in a cup. Thus, it evaporates faster and cools faster in a saucer than in a cup. For this reason we able to sip hot tea or milk faster from a saucer rather than a cup.

Question 5:What type of clothes should we wear in summer?

Solution:We should wear light colored cotton clothes in summer because1. Cotton is a good absorber of water/sweat. It provides more surface area for the sweat to evaporate. 

2. Light colours absorb less heat.

So, wearing light coloured cotton clothes helps us feeling cool and comfortable.



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