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Transfer of heat - class-XI

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A geyser heats water flowing at the rate of 4 litre per minutes from 30 C to 85 C. If the geyser operates on gas burner then the amount of heat used per minute is :

  1. $9.24\times { 10 }^{ 5 }$J

  2. $6.24\times { 10 }^{ 7 }$J

  3. $9.24\times { 10 }^{ 7 }$J

  4. $6.24\times { 10 }^{ 5 }$J


Correct Option: A
Explanation:

For one minute

$H=mC\theta$
$=4kg\times 4200\times55\=924000J\=9.24\times 10^5j$

A 2 m long wire of resistance 4 ohm and diameter 0.64 mm is coated with plastic insulation of thickness 0.06 mm, when a current of 5 ampere flows through the wire, find the temperature difference across the insulation in steady state if $k=0.16\times { 10 }^{ -2 }cal/\left( cm{ C }^{ 0 }sec \right) $ 

  1. ${ 3 }^{ \circ }C$

  2. ${ 2 }^{ \circ }C$

  3. ${ 4 }^{ \circ }C$

  4. ${ 1 }^{ \circ }C$


Correct Option: A

M g of ice at ${ 0 }^{ \circ  }C$ is mixed with M g of water at ${ 10 }^{ \circ  }C.$ The final temperature is

  1. ${ 8 }^{ \circ }C$

  2. ${ 6 }^{ \circ }C$

  3. ${ 4 }^{ \circ }C$

  4. ${ 0 }^{ \circ }C$


Correct Option: A

Name a medium which is a good insulator of heat.

  1. Still (or trapped) air

  2. Oil

  3. Steam

  4. solid copper


Correct Option: A
Explanation:
Trapped(still) air is good insulator.
Thermal conductivity of air is small as compared to solid and liquid. Eg- glass conducts 30 times more power per unit distance per unit temperature than air.
The less dense the material, the less thermal conductivity. And gas(air) is least dense than solid and liquid.

A cotton sheet is ironed with hot electricity. How is energy transferred through the metal base of the iron to the sheet?

  1. by conduction only

  2. by convection only

  3. by radiation only

  4. by convection and radiation only


Correct Option: A
Explanation:
Conduction occurs when two objects at different temperatures are in contact with each other. Heat flows from the warmer to the cooler object until they are both at the same temperature.
The iron and cotton sheet is in contact with each other so, there is conduction between them.

Energy transformation while ironing clothes takes out their wrinkles and makes them smooth. This takes the heat, which is one type of energy. In the iron, electrical energy is used, and it is transformed into heat energy.

In the following solids thermal conductivity is maximum for :

  1. copper

  2. aluminium

  3. gold

  4. silver


Correct Option: D
Explanation:

This is a knowledge based question; also remember that copper is used in electrical wiring only because it is cheaper than silver; copper has lower conductivity than silver.

Two layers of cloth of equal thickness provide warmer covering than a single layer of cloth of double the thickness, because they :

  1. behave like a thermos

  2. have lesser thickness

  3. allow heat from atmosphere to the body

  4. enclose between them a layer of air


Correct Option: D
Explanation:

Air is a bad conductor of heat, hence if layer of air is isolated between two layers of cloth, warmer covering will be provided than if only one layer of cloth, where only body is isolated from surrounding air by cloth. 

Thermoflasks and doors of refrigerators have two layered structure with an insulator in between so as:

  1. to allow more heat to pass through it

  2. not to let heat flow through it

  3. to make it stronger

  4. to beautify it


Correct Option: B
Explanation:

Insulator between the two layers prevent the heat exchange.

Mercury is generally used in thermometer because it has a

  1. High fluidity

  2. High density

  3. High coefficient of expansion

  4. High specific heat


Correct Option: C
Explanation:

Most metals are good conductors of heat and they are solids at room temperature. Mercury is the only one in liquid state at room temperature. It's used in thermometers because it has high coefficient of expansion. Hence, the slightest change in temperature is notable when it's used in a thermometer.

Which of the following is a good conductor of heat?

  1. Plastic

  2. Mercury

  3. Water

  4. Alcohol


Correct Option: B
Explanation:

Mercury is categorized under metasl and we know that metals conduct heat better than non-metals.

So mercury is the answer.

What type of conductor should we used to make water pipes in cold countries?

  1. Good conductor

  2. Poor conductor or bad conductor

  3. Material does not help in such cases

  4. None of the above


Correct Option: B
Explanation:

Poor conductor should be used, so that they will not allow heat to pass from water inside the pipe to outside atmosphere to prevent water from freezing. It will help pipes from busting.

On a cold day when a room temperature is $15^oC$, the metallic cap of a pen becomes much colder than its plastic body, though both are at the same temperature of $15^oC$, because

  1. metals have higher thermal capacity than plastics

  2. plastics have a lower density than metals

  3. metals are good conductor of heat

  4. plastics have a higher thermal conductivity than metals


Correct Option: C
Explanation:

On a cold day when a room temperature is $15^oC$, the metallic cap of a pen becomes much colder than its plastic body, though both are at the same temperature of $15^oC$ because metals are good conductor of heat, so they could absorb and release heat in a better way than insulators.

Two thin walled sphere of different materials ,one with double the radius and one fourth wall thickness of the other are filled with ice If the time taken for complete melting of ice in the sphere of larger radius is $25$ minutes and that for smaller one is $16$ minutes,the ratio of thermal conductivities of the materials of larger sphere to the smaller sphere is  

  1. $4:5$

  2. $25:1$

  3. $1:25$

  4. $8:25$


Correct Option: D

Iron, lead and brass spheres of equal masses are heated to a common temperature and are kept on a sheet of wax. The sphere that passes through the plate first is (lead 0.03 $\operatorname { cal } / \mathrm { g } / ^ { \circ } \mathrm { C }$, iron 0.11 $\operatorname { cal } / \mathrm { g } / ^ { \circ } \mathrm { C }$, brass 0.08 $\operatorname { cal } / \mathrm { g } / ^ { \circ } \mathrm { C }$) 

  1. lead

  2. brass

  3. iron

  4. all at the same time


Correct Option: D

Glaciers melt:

  1. first at the bootom due to decress in pressure

  2. first at the top due to iuncrease in pressure

  3. first at the bottom due to increase in pressure

  4. first at the top due to increase in pressure


Correct Option: C

Two rods having thermal conductivities in the ratio of 5:3 and having equal length length and equal cross-section are joined by face to face. If the temperature of free end of first rod is $100^oC$ and temperature of  free end of second rod is $20^oc$, then temperature of the junction, is-

  1. $90^oC$

  2. $85^oC$

  3. $70^oC$

  4. $50^oC$


Correct Option: C
Explanation:

Let the thermal conductivity of first rod be $5 K$

Let the thermal conductivity of second rod be $3 k$
now, sum of heat current flowing through the junction =0
$\begin{array}{l} \frac { { 5KA\left( { 100-T } \right)  } }{ x } +\frac { { 3KA\left( { 20-T } \right)  } }{ x } =0 \ 500-5T+60-3T=0 \ 8T=560 \ \therefore T={ 70^{ 0 } }C \end{array}$

Select and write the most appropriate answer from the given aternative in question:
Which of the following substances is ductile?

  1. Glass

  2. High carbon steel

  3. Steel

  4. Copper


Correct Option: C

Two walls of thickness $d _1$ and $d _2$, thermal conductivities $K _1$ and $K _2$ are in contact. In the steady state if the temperatures at the outer surfaces are $T _1$ and $T _2$, the temperature at the common wall will be

  1. $\dfrac{K _1T _1+K _2T _2}{d _1+d _2}$

  2. $\dfrac{K _1T _1d _2+K _2T _2d _1}{K _1d _2+K _2d _1}$

  3. $\dfrac{(K _1d _1+K _2d _2)T _1T _2}{T _1+T _2}$

  4. $\dfrac{K _1d _1T _1+K _2d _2T _2}{K _1d _1+K _2d _2}$


Correct Option: B

$\triangle { H }^{ \circ  }$ for reaction: 
${ F } _{ 2 }+2HCI\rightarrow 2HF+{ CI } _{ 2 }$
is equal to -352.8kJ. If $\triangle { H } _{ f }^{ \circ  }$ for HF is -268.3 kJ ${ mol }^{ -1 }$ then ${ \triangle H } _{ f }^{ \circ  }$ of HCI would be:- 

  1. -22 kJ ${ mol }^{ -1 }$

  2. 88.0 kJ ${ mol }^{ -1 }$

  3. 01.0 kJ${ mol }^{ -1 }$

  4. None


Correct Option: C

A hetaed smooth metallic body is allowed to cool in air. Which of the following statements about its heat loss is incorrect?

  1. Convection currents in the air aid the process of heat loss.

  2. Conduction is the main mode of heta loss as the body is a good conductor of heat

  3. The rate of heat loss by thermal radiation is increased due to its metallic surface.

  4. The rate of heat loss decreases as the temperature of teh body nears room temperature


Correct Option: C

Spheres $P$ and $Q$ are uniformly constructed from the same material which is a good conductor of heat and the radius of $Q$is thrice the radius of $P$. The rate of fall of temperature of $P$ is $x$ times that of $Q$ when both are at the same surface temperature. The value of $x$ is:

  1. $1/4$

  2. $1/3$

  3. $3$

  4. $4$


Correct Option: C

If we convert a sphere of radius $'r'$ into a cylinder of radius $r$ at same temperature the rate of heat loss will  becomes if both are placed at same surrounding-

  1. $7/6$

  2. $6/7$

  3. $4/3$

  4. remain same


Correct Option: A

A sphere, a cube and a thin circular plate, all of same material and same mass, are initially heated to same high temperature. Choose the correct statement.

  1. The plate will cool fastest and cube the slowest

  2. The sphere will cool faster and cube and the slowest

  3. The plate will cool faster and sphere the slowest

  4. The cube will cool fastest and plate the slowest.


Correct Option: C

A metal cylinder of mass 0.5 kg is heated electrically by a 12 W heater in a room and cylinder temperature rises uniformly to $ 25^oC in 5 min $ excess temperature surroundings,

  1. The rate of loss of heat of the cylinder to surrounding at $ 20^oC $ is 2 W

  2. The rate of loss heat of the cylinder to surrounding at $ 45^oC $ is 12 W

  3. Specific heat capacity of metal is $ \frac {240}{Ib(3/2)} $

  4. None of these


Correct Option: B

Heat current is maximum in which of the following (rods are of identical dimension)

  1. Copper

  2. Copper steel

  3. Steel Copper

  4. Steel


Correct Option: A

Assertion (A): When hot water is poured in athick glass tumbler then the tumbler breaks.
Reason (R): Glass is a bad conductor of heat

  1. A and R are correct and R is correct explanation for A

  2. A and R are correct and R is not correct explanation for A

  3. A is true and R is false

  4. A is wrong and R is true.


Correct Option: A
Explanation:

Since glass is bad conductor of heat the heat will try to escape but the glass would not allow it and in the process ultimately glass breaks down.

Metals are good conductors of heat because

  1. They contain large number of free electrons

  2. Their atoms are relatively apart

  3. Their atoms collide frequently

  4. They have reflecting surfaces


Correct Option: A
Explanation:

Free electrons are not associated to any atom in particular. They are usually the valence electrons of the metal atoms and are loosely bound. These electrons form a "charge fluid" that travels from one place to other in the conductor and thus convey electric current.

In the Ingen Hausz's experiment, the wax melts up to lengths $10cm$ and $25cm$ on two identical rods of different materials. The ratio of thermal conductivities of the two materials is

  1. $1:6.25$

  2. $6.25:1$

  3. $1: $$\sqrt{2.5}$

  4. $1:2.5$


Correct Option: D
Explanation:

In the Ingen Hauszs experiment, as rate of heat transfer is constant
$\dfrac { { K } _{ 1 } }{ { K } _{ 2 } } =\dfrac { { l } _{ 1 } }{ { { l } _{ 2 } } } $
So, putting the value in above formula's we find
$\dfrac{{K} _{1}}{{K} _{2}}=\dfrac{10}{25}=\dfrac{1}{2.5}$

Two blocks of steel A and B, A being two times heavier than B, are at 40$^o$C. The ratio of heat content of A to B is:

  1. 1

  2. 4

  3. 2

  4. $\displaystyle \frac{1}{2}$


Correct Option: C
Explanation:
Let the mass of block B be $m$.
So, mass of block A is $2m$
Both are made of steel, so, both has same specific heat capacity (let 'S')

So, $\cfrac{Heat\;Capacity\;(A)}{Heat\;Capacity\;(B)}=\cfrac{2ms}{1ms}=2$

Electric heaters used for cooking have the filament or the heating coil on a plate made up of clay because:

  1. clay is a bad conductor of heat

  2. clay is a bad conductor of electricity

  3. clay is necessary for good taste

  4. both A & B


Correct Option: D
Explanation:
Electric heaters used for cooking have the filament or the heating coil on a plate made up of clay because clay is bad conductor of heat and electricity.

Heat capacity of clay is $0.33cal/g^oc$ so bad conductor of heat.
And clay is an insulator, so bad conductor of electricity.

Thermocole lined box is used as a cold storage because.

  1. Thermocole is a bad conductor

  2. It is cheaper

  3. It is easier to construct

  4. None of these


Correct Option: A
Explanation:

Thermocole lined box is used as cold storage because these material is a poor conductor of heat . And it has millions of tiny air bubbles that show the progress of heat through material.

There are two hollow spheres made of different materials, one with double the radius and one fourth wall thickness of the other are filled with ice. If the time taken for melting the ice completely in larger sphere is $25$ minutes and that for smaller sphere is $16$ minutes, the ratio of the thermal conductivity of the larger sphere to the smaller sphere is :

  1. $4:5$

  2. $5:4$

  3. $25:8$

  4. $8:25$


Correct Option: D
Explanation:

Smaller sphere

Radius $\to \dfrac{R}{2}$. wall thickness $\to 4d$

Larger sphere
Radius $\to R$, wall thickness $\to d$

Vol of ice in smaller sphere $= \dfrac{4}{3} \pi \left(\dfrac{R}{2} - 4d\right)^3$

$m _S = $ Mass of ice in smaller sphere $=\rho _{ice} \times \dfrac{4}{3}\pi \left(\dfrac{R}{2} - 4d\right)^3$

$m _L = $ Mass of ice in larger sphere $= \rho _{ice} \times \dfrac{4}{3} \pi (r-d)^3$

Heat required to melt $m _S = m _sL = \dfrac{4}{3}\pi \left(\dfrac{R}{2} 4d\right)^3\times \rho _{ice} \times L = Q _s$        ...(i)

Heat required to melt $m _L = m _l L = \dfrac{4}{3} \pi (R-d)^3 \times \rho _{ice} \times L = Q _L$          ...(ii)

$\dfrac{Q}{t} = \dfrac{KA}{x} (\Delta T)$

$\dfrac{Q _s}{16} = \dfrac{K _s4\pi\left(\dfrac{R}{2}\right)^2}{4d}\Delta T$      ...(for small sphere)      ...(1)

$\dfrac{A _L}{25} = \dfrac{K _24\pi R^2}{d}\Delta T$        ...(for large sphere)   ....(2)

Dividing eq(1)  by eq(2)
$\therefore \dfrac{Q _L}{25} \times \dfrac{16}{Q _s} = \left(\dfrac{K _L}{K _S}\right)\dfrac{4\pi R^2\Delta T\times 4d}{4\pi\left(\dfrac{R}{2}\right)^2\Delta T \times d}$

$\therefore \dfrac{Q _L}{Q _S} \times \dfrac{16}{25} = \left(\dfrac{K _L}{K _S}\right)\times 16$

but $\dfrac{Q _L}{Q _S} = \dfrac{(R-d)^3}{\left(\dfrac{R}{2}-4d\right)^3}$

here $R > > d$,

$\therefore \dfrac{Q _L}{Q _S} = \dfrac{R^3}{\left(\dfrac{R}{2}\right)^3} = 8$

$\therefore \dfrac{8}{25} = \dfrac{K _L}{K _S}$

a corked bottle full of water when frozen will break because.

  1. The volume of water increases on freezing

  2. The volume of water decreases on freezing

  3. The bottle contracts on freezing

  4. Glass is a bad conductor of heat


Correct Option: A
Explanation:
A corked bottle of water on being frozen at $0^{\circ}$ undergoes anomalous expansion of water between $4^{\circ}$ and $0^{\circ}$ wherein density of water increases on cooling , causing expansion due to orderly hydrogen bonding, this increasing volume cracks the bottle.
$Density=\cfrac{Mass}{Volume}$
$\Rightarrow D\propto \cfrac{1}{V}$
$\Rightarrow D\uparrow\Rightarrow V\downarrow$

Read the given statements and select the correct option.
Statement 1: An iron ball at ${35}^{o}C$ is dropped in a mug containing water at $305.15K$. Then the heat will flow from the water to the iron ball.
Statement 2: In convection, heated molecules of a liquid themselves move to carry heat from the hot region to the cold region.

  1. Both statement 1 and 2 are true and statement 2 is the correct explanation of statement 1

  2. Both statement 1 and 2 are true and statement 2 is not the correct explanation of statement 1

  3. Statement 1 is true but statement 2 is false

  4. Statement 1 is false and statement 2 is true


Correct Option: D
Explanation:

${35}^{o}C$ is equivalent to $(273.15+35)308.15K$. So iron ball is at higher temperature and heat will flow from iron ball to the water.

In a room contain air , heat can go from one place to another

  1. By condition only

  2. by convection only

  3. By radiation only

  4. By all the three modes


Correct Option: D

Which of the following is a good conductor of heat?

  1. Steel

  2. Glass

  3. Wood

  4. Rubber


Correct Option: A
Explanation:

Steel being an alloy of metals, it has free electrons in its atoms. They start moving along with the heat flow and help in the conduction of heat. All metals are good conductors. The other three being non-metals, do not have free electrons. Hence they are bad conductors

Heat travels much faster in insulators than in conductors.

  1. True

  2. False


Correct Option: B
Explanation:
The statement if false, heat travels much faster in insulators than in conductors.
Heat travels faster in conductor. Insulators donot even conduct heat, When heat is consumed by the conductor, it has 3 modes of transfer of heat conduction, convection and radiation.

Which of the following is/are bad conductors of heat?

  1. Glass

  2. Aluminium

  3. Iron

  4. Wood


Correct Option: A,D
Explanation:

All metals are good conductors while non-metals are bad conductors of heat.

Name a metal among the following having highest heat conductivity .

  1. Silver

  2. Copper

  3. Aluminium

  4. Brass


Correct Option: A
Explanation:
Following are the thermal conductivities of the following metals and alloys: ( in $wK/m$ )
$Silver-430 \\ Copper-400 \\ Aluminium-235 \\ Brass-109$
Order of thermal (heat) conductivity:
$Silver \gt Copper \gt Aluminium \gt Brass$
So, Silver has highest thermal conductivity

When we touch a steel rod and a paper simultaneously, we feel that the rod is colder because:

  1. iron being a good conductor conducts more heat from our body

  2. paper being a good conductor conducts more heat from our body

  3. more heat flows from the iron to our body

  4. more heat flows from the paper to our body


Correct Option: A
Explanation:

When we touch a steel rod and a paper simultaneously in winter, we feel the rod is comparatively colder because steel being a good conductor of heat, heat from our hand flows to steel but there is no transfer of heat from our hand to paper as it is an insulator of heat. So we don't feel cold when we touch a paper but we do when we touch a steel rod.

A good insulator of heat is

  1. copper

  2. mercury

  3. trapped air

  4. iron


Correct Option: C
Explanation:

thermal conductor is a material that allows energy in the form of heat, to be transferred within the material, without any movement of the material itself. Eg. Metals.

An insulator is a material that does not allow a transfer of electricity or energy. Materials that are poor thermal conductors can also be described as being good thermal insulators.Eg. trapped air

Which of the following statement is true?

  1. Metals are bad conductors of heat

  2. In gases, heat is transferred by conduction

  3. In conduction, molecules move from hotter to colder parts transmitting energy

  4. Metals conduct heat better than the gases.


Correct Option: D
Explanation:
Metals conduct heat better than gases.
Order of conduction of heat
Solid $\gt$ Liquid $\gt$ Gas

Which of the following are good conductors of heat?

  1. Metals

  2. Glass

  3. Water

  4. Wood


Correct Option: A
Explanation:

Metals are generally good conductors of heat.
Non - metals are poor conductors of heat.

Which of the following is the very poor conductor of heat ?

  1. Water

  2. Metals

  3. Liquid other than water

  4. Steam


Correct Option: A
Explanation:

Water is the poor conductor among all. As it is liquid and liquids generally have low heat conductivity than solids. Tighter the molecules are held, more the vibrational energy can transfer between them, heat is no more than vibrating molecules. If we talk about steam, its molecules are less tightly held. But it's important to note that we are talking here of heat conductivity not convection or radiation and contact surface area with heat source.

Assertion (A): Woolen clothes keep the body warm in winter
Reason (R): Air is bad conductor of heat

  1. Both A and R are true,

  2. Both A and R are false

  3. Both A and R are true, R is correct explanation of A

  4. Both A and R are true, R is not correct explanation of A


Correct Option: C
Explanation:

Woollen clothes effectively separate the body from surrounding air by entrapping a layer of air.
Since both wool and air are bad conductors of heat on varying levels, it creates separation that keeps bodies warm.

Substances which allow heat to pass through them are called:

  1. Conductors

  2. Insulators

  3. Moderators

  4. None of these


Correct Option: A
Explanation:

Conductors allow heat to pass through them through vibration of the molecules.

A coin is dipped in the molten wax in a glass tube. When we heat the upper part of the glass tube, the wax around the coil will not melt because:

  1. Wax has a very high melting point

  2. Wax is a good conductor of heat

  3. Glass is a good conductor of heat

  4. Wax or glass are bad conductors


Correct Option: D
Explanation:

Glass is a bad conductor of heat hence the heat from the upper part of the glass tube will not transfer easily to the lower part. Having said that, even wax is a bad conductor of heat and won't melt easily. 

Mercury is a good conductor of heat.State true or false.

  1. True

  2. False


Correct Option: A
Explanation:
Mercury is good conductor of heat. (True)
Thermal conductivity of mercury is $8.30W/mK$. This is the fact why it was used in classical, thermometers for measuring temperature.

The best conductor of heat is

  1. Silver

  2. Bronze

  3. Aluminium

  4. Copper


Correct Option: A
Explanation:

Silver is the best conductor of heat among the given options.

When you pour hot tea suddenly on to a glass tumbler, it cracks. Because:

  1. Glass cannot resist heat

  2. Glass expands unevenly around the place of contact with the tea

  3. Tea has chemicals which react with glass tumblers.

  4. The reason is yet to be discovered by the scientists.


Correct Option: B
Explanation:

When the hot tea is poured into the glass tumbler one side of the glass expands while the other side doesn't. Since glass is not a good conductor of heat, it breaks.

Cups are not made of metals. The reason is:

  1. Metals are good conductors

  2. Metals are bad conductors

  3. Metals are expensive

  4. None of the above


Correct Option: A
Explanation:

Metals are good conductors of heat hence a person might get his fingers injured if he holds the hot plate. 

Select the odd one out w.r.t. conduction of heat (gold, copper, mercury, cork)

  1. cork

  2. gold

  3. copper

  4. mercury


Correct Option: A
Explanation:

Cork is a bad conductor of heat rest are good conductors

Define insulator of heat.

  1. Substances through which heat can pass easily are called insulators of heat.

  2. Substances through which heat cannot pass easily are called insulators of heat.

  3. Substance which can easily freeze are called insulators of heat.

  4. Substances which cannot freeze easily are called insulators of heat.


Correct Option: B
Explanation:

Insulators are  through which heat cannot pass easily.

Select the odd one out w.r.t. conduction of heat (gold, silver, copper, asbestos)

  1. asbestos

  2. gold

  3. silver

  4. copper


Correct Option: A
Explanation:

Asbestos is an insulator rest are good conductors of heat

State whether given statement is True or False
Iron is a better conductor of heat than copper

  1. True

  2. False


Correct Option: B
Explanation:
Thermal conductivity is quantity of heat transmitted due to temperature gradient in unit time under steady conditions in a direction normal to surface of unit area.
Thermal conductivity of copper = 386
Thermal conductivity of iron at $68^oC$ is 73

Thermal conductivity of copper is greater than iron.

Select the odd one out w.r.t. conduction of heat (wood, paper, plastic, silver)

  1. silver

  2. wood

  3. paper

  4. plastic


Correct Option: A
Explanation:

Silver is a good conductor of heat rest are bad conductors

Which of the following behaves as insulator?

  1. Ebonite

  2. Mercury

  3. Silver

  4. Copper


Correct Option: A
Explanation:

Ebonite is a very good insulator while mercury, silver and copper are examples of conductors.

Iron have much lower specific heat than:

  1. Steel

  2. Copper

  3. Water

  4. none of the above


Correct Option: C
Explanation:

Metals have much lower specific heat than water because metals require smaller amount of energy to raise their temperature than water .

Conductors become hot easily because they have:

  1. high specific capacity

  2. low specific heat capacity

  3. high freezing point

  4. low freezing point


Correct Option: B

In general, metals have very low :

  1. Boiling Point

  2. Freezing Point

  3. Melting Point

  4. Specific Heat Capacity


Correct Option: D
Explanation:

In conduction, heat is transferred by the vibrations of molecules. The density of conductors is large, it means molecules are close to each other, because of that they can easily transfer the heat quickly through the whole conductor, therefore unit mass of conductors require small heat to raise their temperature through $1^{o}$ i.e. conductors have very low specific heat. 

Specific heat capacity is ______ for conductors of heat and _______ for insulators of heat.

  1. low, low

  2. low, high

  3. high, high

  4. high, low


Correct Option: B
Explanation:

$Q=ms\Delta T$,

where 
$Q: \text{the amount of heat delivered to a body}$
$m: \text{mass of the body}$
$s: \text{specific heat capacity of the body}$
$\Delta T: \text{Change in temperature of the body}$

If $Q\ \text{and}\ m$ are constant, 
$\Delta T \propto \dfrac{1}{s}$

So for small $s, \Delta T$ is more and hence it is better conductor of heat.

Conductors require __________ heat energy to get heated.

  1. More

  2. Same

  3. Less

  4. neutral


Correct Option: C
Explanation:

Conductors have very low specific heat capacity (c) , therefore heat required (Q) to raise their temperature to a certain range is also less by the following relation: $Q\propto c$

Graphite is a conductor of electricity because

  1. it has free valence electrons.

  2. it is a non-metal form of Carbon.

  3. it is an allotrope of Carbon.

  4. Both A and B.


Correct Option: A
Explanation:
Graphite is a conductor of electricity because it has free valence electrons.
Graphite displays the property of both metal and non-metal. Like a metal, graphite is good conductor of electricity due to mobility of electrons in outer valence shells.

Examples of non-conductors include

  1. sulphur.

  2. phosphorus.

  3. wood.

  4. all of these.


Correct Option: D
Explanation:

Sulphur, Phosphorus, Wood are non-conductors of electricity due to no presence of free electrons in outermost shell.

Easy to shape materials like ceramics are used as

  1. conductors.

  2. insulators.

  3. electrodes.

  4. catalysts.


Correct Option: B
Explanation:
Glass, tiles, pottery, porcelain, brick, cement etc. are ceramics.
They are obviously insulators of heat.

Overhead cables are insulated from pylons through

  1. plastic.

  2. ceramics and glass.

  3. rubber.

  4. PVC.


Correct Option: B
Explanation:
Examples of ceramics are clay, bricks, tiles, glass, and cement.
Overhead cable is insulated from pylons through ceramics and glass.
The overhead power lines that are supported by pylons are not covered in insulating materials. However, ceramics or glass insulators are fitted between pylons and wires. This stops electricity flowing down the metal pylons to the ground, where it could hurt or even kill people or animals.

In conductors outer electrons :

  1. are not tightly bound to the nucleus

  2. are tightly bound to the nucleus

  3. never becomes free electrons

  4. are always free to move


Correct Option: A
Explanation:

Conductors can easily conduct electricity because they are loosely bound to the nucleus and they are not engaged in chemical bonding. Conductors have free electrons.

In conductors, electrons can flow because their

    1. ions are free

    2. protons are free

    3. electrons are free and mobile

    4. negative ions are free


    Correct Option: C
    Explanation:

    In conductors, electrons can flow because their electrons are free and mobile metals have free electrons present in outermost orbit i.e. they are mobile in nature. This is the fact due to which they could produce electricity.

    An insulator is a non-metallic substance which :

    1.  allows heat to pass through it

    2. has extremely low resistance to the flow of charge through them

    3. has extremely high resistance to the flow of charge through them

    4. increases current in the circuit


    Correct Option: C
    Explanation:

    An electrical insulator is a material whose internal electric charges do not flow freely because of extremely high resistance. Very little electric current will flow through it under the influence of an electric field.

    Metals are good conductors of electricity than non-metals because:

    1. Metals have free electrons which can move from atom to atom easily

    2. Non-metals have free electrons which can move from atom to atom easily

    3. Metals have bound electrons which cannot move easily

    4. Non-metals have bound electrons which cannot move easily


    Correct Option: A,D
    Explanation:

    Metals have free electrons which can move from atom to atom easily, whereas non-metals do not, their electrons are 'bound' meaning they cannot move easily. That's why metal are usually good conductors than non-metals.

    Poor conductors of electricity consist of

    1. silver

    2. aluminum

    3. distilled water

    4. copper


    Correct Option: C
    Explanation:

    Pure water or distilled water doesnot conduct electricity but tap water, rain water or sea water conduct electricity. For electricity to travel through a liquid movement of charge must take place through the liquid. In tap water, rain water or sea water, there are impurities such as salt of $Na,Mg \; and \; Ca$. They behave as the charge carriers for conduction of electricity. But in distilled water there are no impurities i.e. no ions. There are only neutral water molecules. So, distilled water doesnot conduct electricity.

    Why is electrical wiring usually made from copper?

    1. Because copper is shiny.

    2. Because copper conducts electricity.

    3. Because copper is not magnetic

    4. none of these


    Correct Option: B
    Explanation:

    Copper is usually used for copper wiring because copper conducts electricity. Because electrical conductivity of copper is good enough and it is cheap too. So it is used in wiring.

    Which of the following materials is an electrical conductor?

    1. Silver

    2. Silver-coloured plastic

    3. Cork

    4. Rubber


    Correct Option: A
    Explanation:
    As we know that generally, metals are conductors and non-metals are insulators. That is metal conduct electricity more than that of non-metal.
    SIlver is the only metal present in the list, so it is the only electrical conductor.
    All others are non-metals.

    Which of the following materials is an electrical insulator?

    1. Aluminium

    2. Gold

    3. Rubber

    4. all of these


    Correct Option: C
    Explanation:
    As we know that generally, non-metals are insulators and metals are conductors.
    As rubber is the only non-metal in the list, so it is an electrical insulator.

    Why are insulators important in an electrical circuit?

    1. They make the circuit safe to touch.

    2. Electricity will only flow through insulators.

    3. Light bulbs and buzzers are only made of insulating materials.

    4. All of the .above


    Correct Option: A
    Explanation:

    Insulators are used in circuits, as they don't conduct electricity, they are used for insulation of wire, switches, plugs, etc. So that circuit could be made shock free and safe to touch.

    Why are electrical plugs made of plastic?

    1. Plastic is stronger than all other materials.

    2. Plastic is a good electrical conductor.

    3. Plastic protects people from electricity.

    4. Only plastic can be made into the right shape for a plug


    Correct Option: C
    Explanation:

    Electrical plugs are made up of plastic because plastic protects people from electricity. As we know that plastic is an electrical insulator readily available and cheap. So as to make the plugs shock free, they are made up of plastic.

    Why is electrical wiring usually covered with a layer of plastic?

    1. To make it look pretty

    2. To help electricity flow along the wire

    3. To make it safe

    4. none of these


    Correct Option: C
    Explanation:

    Electrical wiring is usually covered with layer of plastic to make it safe. As we know that plastic is an electrical insulator and it is readily available and cheap. So as to insulate the electricity carrying wire, to make it shock free. It is covered with layer of plastic.

    A material that does NOT let electricity pass through it is called ...

    1. an electrical conductor

    2. an electrical insulator

    3. an electrical appliance

    4. none of these


    Correct Option: B
    Explanation:
    A material that does not allow to electricity to pass through, it is called an electrical insulator.
    They do not have free electrons present in their outer most shell which would work as charge carriers for conduction of electricity.

    Materials that allow electrons to flow through them are known as

    1. Insulator

    2. Conductors

    3. Electrolytes

    4. Bases


    Correct Option: B
    Explanation:

    Materials that allow electrons to flow through them are known as conductors because they consist of free electrons.

    Which of these is a good electrical conductor?

    1. Water

    2. Sweat

    3. The human body

    4. All of the above


    Correct Option: D
    Explanation:
    Water is a good electrical conductor but not distilled water. Tap water, Sea water, rain water etc. conduct electricity as they consists of impurities; salts of $Ca, \; Mg,\; Na$ which behave as charge carriers.

    Sweat conducts electricity although it is mainly water, it still consists of lot of minerals, lactic acid, urea; in short, it is an ionic liquid (electrolyte)

    Human body consists of $75 $% of water and also consists of many minerals and salts. So human body also conducts electricity.

    State whether given statement is True or False
    In a superconductor, electricity will flow for a long time and then stop.

    1. True

    2. False


    Correct Option: B
    Explanation:
    False
    Superconductors are those materials which have exactly zero resistance and expulsion of magnetic flux occurs when they are cooled below certain temperatures.

    State whether given statement is True or False
    Innermost electrons are free to move :

    1. True

    2. False


    Correct Option: B
    Explanation:
    False
    Innermost electrons are not free to move because they are tightly held by the attractive force by the protons present in the nucleus of the element. Only outermost electrons are free to move in conductors.

    When electrons in a material are free to move, the material is:

    1. an insulator

    2. a conductor

    3. a semiconductor

    4. none of these


    Correct Option: B
    Explanation:
    When electrons in a material are free to move, the material is a conductor.
    As only conductors have free electrons present in the outermost shell which are mobile and behave as charge carriers and are conduction electrons.

    What is NOT an example of an insulator in the kitchen?

    1. An oven mitt

    2. A wooden spoon

    3. Pots and pans

    4. A plastic measuring cup


    Correct Option: C
    Explanation:

    Pots and pans are NOT example of insulator, they are conductors of heat, if it was not so; they could not be used for cooking of food. And they are used for cooking; so they are conductors.

    Which of the following would normally be the best conductor?

    1. Copper

    2. Glass

    3. Steel

    4. Silver


    Correct Option: D
    Explanation:
    Among copper, glass, silver and steel, glass is non-metal i.e. insulator; so it has least conductivity.
    Conductivity order:
    Silver $\gt$ Copper $\gt$ Steel
    (in $siemens/m$) at $20^oC$
    $62.1\times 10^6 \gt 59.8\times 10^6 \gt 6.21\times 10^6$

    Which of these could be used to complete an electrical circuit?

    1. A piece of gravel.

    2. A rubber.

    3. A crayon

    4. Scissors made of iron


    Correct Option: D
    Explanation:

    Scissors made of iron could be used to complete an electrical circuit. As iron is a metal and conductor so can conduct electricity easily. And others are non-metals. So they could not conduct electricity and can't complete the circuit.

     Pure Water is an insulator.

    1. True

    2. False


    Correct Option: A
    Explanation:

    Pure water consists of no impurities; impurities such as salts of $Mg,Ca,Na$ are behaving here as charge carriers but since they are not present; there are no ions. They are neutral water molecules. So pure water do not conduct electricity.

    The outermost electrons are __________ and are called conduction electrons :

    1. not free to move in the atom

    2. bound to the protons

    3. static

    4. able to go to nearby atoms


    Correct Option: D
    Explanation:
    The outermost electrons are able to go to nearby atoms and are called conduction electrons.
    Yes the outermost shell electrons are able to go to nearby atoms only during bond formation (ionic bond). They are free or mobile electrons because of that they conduct electricity so they are called conduction electrons.

    Which material is a best conductor?

    1. silver

    2. porcelain

    3. rubber

    4. gold


    Correct Option: A
    Explanation:
    Out of silver, porcelain, rubber, and gold; porcelain and rubber are non-metals i.e. insulators. So
    Now out of silver and gold conductivity of silver ($62.1\times 10^6 siemens/m$) is more than that of gold ($44.2\times 10^6 siemens/m$)

    Which metal is a good conductor of heat?

    1. Gold

    2. Mercury

    3. Lead

    4. Alloys


    Correct Option: A
    Explanation:
    As metals contain free electrons, it transfers the energy given in the form of heat rapidly but in non-metals, it takes time to heat. Gold is metal so it is a good conductor of heat and mercury, lead, alloys are non-metals so they are poor conductors of heat.


    Mud houses are cooler in summer and warmer in winter because

    1. mud is a good conductor of heat

    2. mud is a superconductor of heat

    3. mud is a bad conductor of heat

    4. none of these


    Correct Option: C
    Explanation:

    Mud is a bad conductor of heat. It does not allow the heat to transfer from house to atmosphere in winter and atmosphere to house in summer.

    In case of conductors and insulators, if an electric field is applied then conduction current density$\vec{(J)}$ is:

    1. in the direction of electron flow.

    2. in the direction of proton flow.

    3. in the direction of electric field.

    4. against the direction of electric field.


    Correct Option: B,C
    Explanation:
    Current density, $\overrightarrow { J } =\cfrac { I }{ \overrightarrow { A }  } $
    Current flows in direction of flow of protons. And the direction of electric field is in the direction of flow of electrons.
    And the direction of current density is in the direction of proton flow, so from above statements, current density is also in the direction of electric field.
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