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Introduction to heat - class-IX

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Heat energy produces a sensation of-

  1. warmth

  2. coldness

  3. both warmth and coldness

  4. none of these


Correct Option: A
Explanation:
Heat energy is the result of the movement of tiny particles called atoms, molecules or ions in solids, liquids and gases. Heat energy can be transferred from one object to another. The transfer or flow due to the difference in temperature between the two objects is called heat.
Heat energy produces a sensation of warmth

State whether given statement is True or False
A wooden chair feels colder than an iron chair in winter

  1. True

  2. False


Correct Option: B
Explanation:

Metal conducts heat much better than wood does. Since your hand is hotter than room temperature, both the metal and the wood conduct heat away from it.an iron chair in winter feels colder

State whether given statement is True or False :

Mud houses are hot in summer and cold in winter.

  1. True

  2. False


Correct Option: B
Explanation:

Mud houses have thatched roofs. The insulating effect of the thatch prevents heat from getting in very quickly (cool in summer) and heat getting out very quickly (warm in winter). Secondly, mud houses are made up of mud, which has large pores. As evaporation causes cooling, mud houses feel cooler in summer 

This is why mud houses are cool in summer and hot in winter.

Heat will flow from

  1. Hot body to cold body

  2. Cold body to hot body

  3. two bodies at the same temperature

  4. None of these


Correct Option: A
Explanation:

Heat can be transferred from one place to another by three methods: conduction in solids, convection of fluids (liquids or gases), and radiation through anything that will allow radiation to pass. The method used to transfer heat is usually the one that is the most efficient. If there is a temperature difference in a system, heat will always move from higher to lower temperatures.Heat will flow from Hot body to cold body

Beaker A contains hot water. Beaker B contains cold water. Beaker C contains a mixture of hot and cold water. If initially your hand is put into a beaker containing ice, then putting your hand in which of the beakers A, B or C will give a sensation of warmth?  

  1. A

  2. B

  3. C

  4. All of the above.


Correct Option: D

A thermostat is?

  1. A device used to maintain a constant temperature of a water bath or an oven

  2. A modern type of thermoflask which work on the principle of equipartition of heat energy

  3. An instrument by which the accuracy of thermometers is determined

  4. A device which varies the temperature of a both


Correct Option: A
Explanation:

A thermostat is a device that automatically regulates temperature, or that activates a device when the temperature reaches a certain point.

Thus, it can be used to maintain a constant temperature of a water bath or an oven.
Hence, option A is correct.

Reading of temperature may be same on

  1. Celsius and kelvin scale

  2. Fahrenheit and Celsius scale

  3. Kelvin scale

  4. None of these


Correct Option: B

Three liquids A, B and C are at temperature of $60^{o}C, 55^{o}C$ respectively $4g$ of A mixed with $3g$ of C gives $65^{o} C$ and $2g$ of A mixed with $3g$ of B gives $57^{o}C$. The temperature of the mixture when equal masses of $B$ and $C$ are mixed is 

  1. $52.1^{o}C$

  2. $55^{o}C$

  3. $52.5^{o}C$

  4. $53^{o}C$


Correct Option: A

The temperature of equal masses of three different liquids $A, B$ and $C$ are $12^{o}C, 19^{o}C$ and $28^{o}C$ respectively. the temperature when A and B are mixed is $16^{o}C$, when B and C are mixed is $23^{o}C$ what is the temperature when A and C are mixed 

  1. $31^{o}C$

  2. $20.26^{o}C$

  3. $19.5^{o}C$

  4. $28^{o}C$


Correct Option: A

The standard fixed point for temperature measurement is used these days is :

  1. melting point of ice at S.T.P.

  2. that temperature at which ice, water and water vapour coexist

  3. that temperature at which pure ice and pure water coexist

  4. none of the above


Correct Option: B
Explanation:

(B)The triple point of a substance is unique, i.e. it occurs at one particular set of values of pressure and temperature. The melting point of ice and boiling point of water are not unique. They change with change in value of pressure or due to the presence of impurities in water.

During burning of a candle, different zones of combustion in the flame are listed below:

A. outermost zone
B. innermost zone
C. middle zone
The correct order of temperature of zones is :

  1. $A > B > C$

  2. $C > B > A$

  3. $B > C > A$

  4. $A > C > B$


Correct Option: D
Explanation:

The correct order of temperature of zones of candle flames is -
Outermost zone > Middle zone > innermost zone.
Because outerzone will have the highest temperature and inner zone will have the least temperature.

At what temperature is the Fahrenheit scale reading equal to twice of Celsius ?

  1. $ 40^0C $

  2. $ 160^0C $

  3. $ 80^0C $

  4. $ 100^0C $


Correct Option: B
Explanation:

We know the relation between Fahrenheit scale and degree celsius,


$\dfrac{C-0}{100}=\dfrac{F-32}{180}$

Given,

$F=2C$

Then,

$\dfrac{C}{100}=\dfrac{2C-32}{180}$

$\dfrac{C}{100}=\dfrac{C-16}{90}$

$\implies 9C=10C-160$

$\implies C=160^0C$

A man wishes to fit an aluminium ring on steel rod of 1 cm diameter and found it is 0.01 cm smaller in diameter. How much should the on temperature be raised before it just slips on the
$(\alpha _A = 25 \times 10^{-6}/^oC;$ $10 \times 10^{-6}/^oC)$

  1. $40^oC$

  2. $50^oC$

  3. $25^oC$

  4. $60^oC$


Correct Option: A
Explanation:

${l _2} = {l _1}\left( {1 + {\alpha _A}\Delta T} \right)$

${l _2} = {l _1} + {l _1}{\alpha _A}\Delta T$

$\displaystyle {{{l _2} - {l _1}} \over {{l _1}}} = {\alpha _A}\Delta T$

$\displaystyle {{0.01 \times {{10}^{ - 2}}} \over {1 \times {{10}^{ - 2}} \times 25 \times {{10}^{ - 6}}}} = \Delta T$

$\Delta T = {40^0}C$

Which of the following physical quantities is measured in calories ? 

  1. Heat energy

  2. Force

  3. Momentum

  4. Temperature


Correct Option: A
Explanation:

1 calorie: The amount of energy required to warm $1\ g$ of air-free water from $14.5^oC\ to\ 15.5^oC$ at a constant pressure of $101.325\ kPa$ $(1 atm)$

Name the S.I. unit of heat.

  1. Joule

  2. Kelvin

  3. Degree centigrade

  4. All of the above


Correct Option: A
Explanation:

Answer is (A).

It has the same unit as of energy that's Joule.

State the S.I. unit of heat capacity.

  1. $ J^{-1}K^{-1}$

  2. $ JK^{-2}$

  3. $ JK$

  4. $ JK^{-1}$


Correct Option: D
Explanation:

The S.T. unit of heat capacity is heat required per degree rise in temperature. So it is $JK^{-1}$

1 cal = _________

  1. 10 joules

  2. 4.18 joules

  3. 4.18 dynes

  4. None of these


Correct Option: B
Explanation:

1 cal = 4.18 joules

C.G.S unit of heat is calorie.
S.I. unit of heat is joule.

The SI unit of heat is:

  1. calorie

  2. joule

  3. dyne

  4. newton


Correct Option: B

Therm is a unit of

  1. heat

  2. temperature

  3. thermometry

  4. mass


Correct Option: A
Explanation:

The therm (symbol, thm) is a non-SI unit of heat energy equal to100000 British thermal units (Btu). It is approximately the energy equivalent of burning 100 cubic feet (2.83 cubic metres) – often referred to as 1 CCF – of natural gas.

For a gm molecule of an ideal gas

  1. ${PV}/{T} = 2$ calories

  2. ${PV}/{T} = 4.2$ calories

  3. ${PV}/{T} = 4.31$ calories

  4. ${PV}/{T} = 4.2 \times {10}^{7}$ ergs


Correct Option: B

The quantity of heat energy required to change the temperature of one gram of water by one degree Celsius is known as

  1. 1 joule

  2. 1 kilocalorie

  3. 1 calorie

  4. 1 ampere


Correct Option: C
Explanation:

The amount of heat required to raise the temperature of one gram of water  through $ 1 ^{o}$ (from $14.5^{o}C$ to $15.5^{o}C$), is called one calorie.

One calorie is defined as

  1. The amount of heat energy required to raise the temperature of $1\ g$ water by $1^o\ C$

  2. The amount of heat energy required to raise the temperature of $1\ kg$ water by $1^o\ C$ 

  3. The amount of heat energy required to raise the temperature of $1\ g$ water by $1^o\ F$ 

  4. The amount of power required to raise the temperature of $1\ g$ water by $1^o\ C$ 


Correct Option: A
Explanation:

The amount of heat energy required to raise the temperature of 1 g water by $1^o\ C$ is called one calorie.

1 volt is equivalent to:

  1. $\dfrac { newton }{ second }$

  2. $\dfrac { newton }{ coulomb }$

  3. $\dfrac { joule }{ coulomb }$

  4. $\dfrac { joule }{ second }$


Correct Option: C
Explanation:
Energy, $E=QV$
        $V=\dfrac{E}{R}$
$ \ 1 Volt=1 \ \dfrac{Joule}{Coulomb}$

Hence, option C is correct.

The temperature range in the definition of calorie is

  1. $14.5^{o}C $ to $15.5^{o}C $

  2. $15.5^{o}C $ to $16.5^{o}C $

  3. $1^{o}C $ to $2^{o}C $

  4. $13.5^{o}C $ to $14.5^{o}C $


Correct Option: A
Explanation:

According to the International Committee of Pure Physics, calorie is the standard unit to measure heat. The quantity of heat required to raise 1 gram of water from $14.5^o C \ to \ 15.5^o C$ is defined as a calorie.

1 Joule $=$

  1. $10^8 ergs$

  2. $10^6 ergs$

  3. $10^7 ergs$

  4. $10^{10} ergs$


Correct Option: C
Explanation:

We know,

$1 \ Joule = 10000000 \ ergs = 10^7 \ ergs$
Hence, option C is correct.

Out of the metal balls of same diameter one is solid and other is hollow. Both are heated to the same temperature at $300^{0}C$ and then allowed to cool in the same surroundings then rate of loss of heat will be:

  1. More for hollow sphere

  2. More for solid sphere

  3. Same for both

  4. None of the above


Correct Option: A

The amount of heat required to raise the temperature of 1 kilogram of water by $1:^oC$ is called :

  1. Kilo-calorie

  2. calorie

  3. B. T. U

  4. $calorie/^oC$


Correct Option: A
Explanation:

The amount of heat required to raise the temperature of 1 kilo gram of water by $1:^oC$ is called kilo calorie.

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