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

Q.1. What is heat?

Ans: Heat is form of energy that produces feeling of hotness. It is measured in Joule . Calorie is used to measure energy value of food. 1 cal. =4.2 joule

Q. 2.What is energy?

Ans: Energy is capacity to do work. Energy is neither created nor destroyed it can only changed one form to another.

Q. 3.What are the effects of heat?

Ans: Heat cause many change in living and non living thing. They are 1. Heat increase in temperature  2. Heat expand a substance    3. Heat changes the state    4. Heat bring chemical change 5.Heat effect living thing

Q.4. What is temperature?

Ans: The degree of hotness and coldness of a body is called temperature of body. Thermometer is an instrument used to measure temperature. It is work on principle of expansion in liquid on heating. It is measured in Celsius and Fahrenheit scale but for scientific work Kelvin scale is used.

0F = (9/5 x 0C) +32  and  oC = (9/5)(F- 32) and K= C + 273o

Q. 5.What is thermometry?

Ans: The science of measurement of temperature is known as thermometry

Q.6. What are different types of thermometer?

Ans: Thermometer: It consist of long narrow glass tube having fine bore.There is a glass bulb filled with liquid mostly mercury at the one end and sealed at other end. There is small bend just above bulb called Kink.  it does not allow the mercury to fall as soon as taken out from our mouth.

(i). Laboratory Thermometer: It ranges from -10oC to 110oC

(ii) Clinical thermometer: It is used to measure body temperature. It ranges from 35oC to 42oC and 94oF to 108oF.  Mercury thermometer can measure temperature from -35oC to 357oC.

(iii) Alcohol thermometer used to measure temp. from -125oC to 50oC.

Q. 7.What is the use of the m a x i m u m - m i n i m u m thermometer?

Ans:  The maximum and minimum temperatures atmosphere reported in weather reports which is measured by a thermometer called the m a x i m u m - m i n i m u m thermometer.

Q.8. What is the normal body temperature?

Ans: 37oC or 98.6oF.

Q.9. Why mercury preferred in thermometers?

Ans: Mercury used due to following reasons (i) It expand uniformly   (ii) It does not stick to wall  (iii) It is shiny and easy to see  (iv) It remain liquid at room temperature.

Q.10. Find at what temperature measurement on Celsius equal to Fahrenheit.

[Ans: - 400]

Q.11. Find at what temperature measurement on Fahrenheit double of Celsius

[Ans: 1600]

Q. 12.What is thermal expansion (enlargement)?

Ans: The expansion produced in substance on heating is called thermal expansion. When we heat a substance its molecules gain energy and start vibrating rapidly and spread out . As a result a substance expands.

Q.13. Why does gas expand more than solid and liquid?

Ans: Gas expands more than solid and liquid because its molecules are bound with very weak force of attraction.

Q.14. A bimetallic strip made of brass and iron welded together. When it is heated, the strip bend why?

Ans: Brass expand and contract more than iron on heating and cooling. This unequal expansion and contraction bent the strip.

Q. 15.The same quantity of heat supplied to same amount of different substances does not necessarily produce the same increase in temperature. Why?

Ans: Different substances absorb differently that depends on (a) Mass of body (b) change in temperature (c) Nature of substance. For this reason  the same quantity of heat supplied to same amount of different substances does not necessarily produce the same increase in temperature

Q.16. If difference in temperature between A and B is 50C , What is the difference in Kelvin?

Ans: 5K

Q.17. Give some examples expansion causes problems?

Ans (i). Gaps are left between two sections of railway tracks that allow expansion in summer and protect from bending causing accident.

(ii). During summer, iron expands and cause serious accidents. To allow this expansion Space left between two sections of rail tracks.

(ii). When we pour hot liquid, sometime glass tumbler crack because inner wall get heated quickly and expand than outer wall. A Pyrex glass resist from this unequal expansion.

Q. 18.Explain one  good use of expansion:

1. In fire alarm expansion put in good use. The alarm contains two strips of iron and brass bolted together. When it is heated because of fire, brass expands more than iron and bends towards iron. Bell starts ringing. As the fire put out strip gets cooled and straighten again.

Q.19. What is heat capacity?

Ans: The amount of heat required to raise temperature of a substance by 10C . It is different for different substance. It depends on (a) Mass of body (b) change in temperature (c) Nature of substance. Q µ m    and Q µ t    Þ Q = S m t

Here, S is a constant and named Specific heat of body.

Q. 20.What is specific heat capacity?

Ans. The amount of heat required to raise the temperature of 1 kg  by 10C . Water has highest heat capacity. SI unit is j/kg0C

Q.21. Define melting and boiling point

Ans .The temperature at which solid melts is called Melting point. Melting point of ice is 00C and wax is 630 C. The temperature at which liquid changes into vapour is called boiling point.

Q. 22.What is latent heat of fusion?

Ans: Latent heat or hidden is amount of heat that only change state not temperature.

The amount of heat required to melt 1 kg substance from solid to liquid without change of temperature is called latent heat of fusion.

Q. 23.What is latent heat of vaporization?

Ans: The amount of heat required to change 1 kg substance from liquid to vapour state without change of temperature is called latent heat of vaporization.

Q. 24.Why stem burn more than boiled water?

Ans: Because stem has more latent heat than boiled water[ about 2260j/g]

Q.25. why does water used as coolant in car?

Ans: Water has high specific capacity this makes water to take long time to heat up by absorbing very large quantity of heat. Therefore water used as coolant in car and factories.

Q.26. What are different mode of transfer of heat?

Ans: Heat flows from higher to lower temperature till both body attend same temperature.

There are three mode of transfer of heat

(a) Conduction: The mode of transfer of heat from molecules to molecules without movement of particles.. Conduction takes place in solid as its molecules ate closely packed. Solids, metals and alloy are good conductor. Non metals, plastic glass are bad conductor of heat.

(b)Convection: The mode of transfer of heat from molecules to molecules with movement of particles. In liquids and gasses heat transferred by convection as molecules are far apart from each other .

(c) Radiation: The mode of transfer of heat that does not require any material medium. Heat of sun reach the earth by radiation.

Q.27. At what factor heat absorbed on radiation by body depends on?

Ans: (a) Distance between body and source of heat

(b) its colour(Black coloured surface absorb more than white surfaces)

Q. 29. A desert is very hot in the day and very cold at night?

Ans: Due to low specific heat capacity air above land heated up quickly in the day and cooled quickly at night. For this reason a desert is very hot in the day and very cold at night.

Q.30. Describe construction and working of thermos flask.

Ans: thermos flask is doubled walled glass vessel. Air inside glass wall prevents conduction and convection. Glass walls are silvered on the inside. Silver is good reflector of heat this prevent heat loss due to radiation. If we remove the silvering thermos flask not keep liquids hot or cold for quite a long time.  CLASS VII  Science (Physics) Ch- Heat and Temperature Question with solution Part-2 CLASS VII  Science (Physics) Ch- Heat and Temperature extra scoring notes Chapter 21 Temperature, Heat, and Expansion worksheet Download  Chapter 21 Temperature, Heat, and Expansion Chapter Assessment  Download