VII Physics:Chapter- Heat and Temperature Question with solution

CLASS VII  Science (Physics) Ch- Heat and Temperature Question with solution

Q1. Define the following terms:

a.) Temperature b.) Thermometer c.) Conductor of heat d.) Insulator of heat.

Ans: (a.) Temperature is a measure of the degree of hotness and coldness of an object.

S.I unit of Temperature is Kelvin. Other Units are degree Celsius and  degree Fahrenheit}

b.) Thermometer is a device used for measuring temperatures.

c.) Materials which allow heat to pass through them easily are called conductors of heat. e.g. iron, aluminum, copper etc.

d.) Materials which do not allow heat to pass through them easily are called insulators of heat. E.g. plastic, wood etc and Water , air are poor conductors of heat

Q2. i.) What is Clinical thermometer?

ii.) Name the liquid used in this thermometer.

iii.) What is the range of this thermometer?

(iv) Why digital thermometers are used these days

Ans.: i.) Thermometer that measures our body temperature is called a Clinical thermometer.

ii.) Mercury.  iii.) 35oC to 42oC.

(iv) Mercury is a poisonous metal. If a thermometer breaks, when in mouth, one is exposed to mercury. To overcome this, digital thermometers are used these days.

Q3. What is the normal temperature of healthy human body?

Ans: 37oC.

Q4. What is the range of Laboratory thermometer?

Ans: - 10oC to 110oC.

Q5. We can not use Laboratory thermometer to measure our body temperature. Why?

Ans: There is no ‘kink’ in laboratory thermometer. Therefore the temperature will fall as soon as we remove the thermometer from the mouth & we will not be able to measure the correct temperature of the body.

Q6. What is the use of ‘kink’ in clinical thermometer?

Ans: ‘Kink’ is provided in the clinical thermometer which does not allow the mercury to come down on its own and  we can note the measured temperature even after some time.

Q7. Why is mercury used in thermometer?

Ans: Mercury is used in thermometer because of following reasons:

i) It does not stick to the walls of capillary tube.

ii) Its silvery shine helps us to see temperature accurately.

iii) Its expansion is uniform.

iv) It does not vaporize easily.

Q 8. Give reason for each of the following:

a.) Cooking utensils are made up of metals.

b.) Cooking utensils & tea kettles are provided with handles made up of wood & ebonite.

c.) Light coloured clothes are more suitable in summer & dark clothes in winter.

d.) Woollen Clothes keep us warm in winter.

e) The base of cooking utensil is painted black.

Ans: a.) Cooking utensils are made up of metals. Being very good conductors, they heat up very quickly and  therefore cooks food in shorter time.

b) Wood and  ebonite are poor conductors of heat, therefore the handle does not get heated and  we can hold the hot utensil quite comfortably.

c) White or light coloured clothes are more suitable in summer because they absorb very little of the sun’s heat & keep our bodies cool. While black or dark coloured clothes are suitable in winter because they absorb most of the radiant heat of the sun and  keep us warm.

d) Wool is a poor conductor of heat. Moreover, there is air trapped in between the wool fibers.This prevents the flow of heat from our body to the surroundings. So we feel warm.

e) So that it absorbs more heat & cooks food in shorter time.

Q9. Suppose you are given the choice in winter of using either one thick blanket or two thin blankets joined together. What would you choose & why?

Ans: We prefer two thin blankets joined together because the air trapped between two blankets acts as an insulator and does not allow the body heat to escape.

Q10. Name the three processes of transfer of heat & explain them?

Ans: Conduction, Convection & Radiation are three processes of transfer of heat.

Conduction: It is the process of transfer of heat in solids. In this process the molecules of the solid pass the heat from one to another, without themselves moving from their positions.

Convection: It is the process of transfer of heat in liquids & gases. In convection, the molecules themselves move from one place to another, carrying heat with them.

{Note: Solids are not heated by convection because the molecules of a solid are not free to move from one place to another; they can only vibrate about fixed position.}

Radiation: It is the process of heat transfer from a hot body to a colder body without heating the space between the two. The transfer of heat by radiation does not require any medium.

Q11. What are Land & Sea Breezes?

Ans: Sea Breezes: During the day, the land is heated by sun to a higher temperature than the water in the sea. Air over the land is heated, becomes lighter & rises while the cooler air from the sea blows towards land to take its place. This is called the sea breeze.

Land Breeze: At night, the land is no longer heated by the sun. It therefore cools. But the land cools much faster than the sea. Therefore, the sea is warmer than the land at night. So at night a current of air blows from the colder land to the warmer sea. This is called the land breeze.

Q12. Name the physical quantity that determines the direction of heat flow?

Ans: Temperature. Heat flows from high temperature to low temperature till the temperature of both the bodies in contact is same.

Q13.Fill in the blanks:

(i) Temperature is the measure of _________ of an object.(Hotness)

(ii) The thermometer used to measure human body temperature is called ________. (Clinical thermometer)

(iii) The normal temperature of human body is ___________OC.  (37)

(iv)  A ___________ near the bulb of a clinical thermometer prevents mercury level from falling of its own. (Klink)

(v) The water and air are ___________ conductors of heat.(poor)

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CLASS VII  Science (Physics) Ch- Heat and Temperature Question with solution Part-1