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When vapour condenses into liquid

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Important Questions on Heat and Thermodynamics

MEDIUM

General Science>Physics>Heat and Thermodynamics>Change of State

A simple pendulum made of a bob of mass m and a metallic wire of a negligible mass has a time period of

2 s

T = 0 ° C

. If the temperature of the wire is increased, and the corresponding change in its time period is plotted against its temperature, the resulting graph is a line of slope

S

. If the coefficient of linear expansion of metal is

α

, then the value of

S

MEDIUM

General Science>Physics>Heat and Thermodynamics>Change of State

Consider two thermometers,

T_{1}

and

T_{2}

of equal length which can be used to measure temperature over the range

θ_{1}

θ_{2} . T_{1}

, contains mercury as a thermometric liquid while

T_{2}

contains bromine. The volumes of the two liquids are the same at the temperature,

θ_{1}

. The volumetric coefficients of expansion of mercury and bromine are

18 \times 10^{- 5} K^{- 1}

and

108 \times 10^{- 5} K^{- 1}

, respectively. The increase in the length of each liquid is the same for the same increase in temperature. If the diameters of the capillary tubes of the two thermometers are

d_{1}

and

d_{2}

respectively, then the ratio

d_{1} : d_{2}

would be closest to:

HARD

General Science>Physics>Heat and Thermodynamics>Change of State

A pendulum clock loses 12 s a day if the temperature is

40^{o}

C and gains 4s a day if the temperature is

20^{o}

C. The temperature at which the clock will show correct time, and the co-efficient of linear expansion

(α)

of the metal of the pendulum shaft are respectively:

MEDIUM

General Science>Physics>Heat and Thermodynamics>Change of State

A uniform cylindrical rod of length

L

and radius r, is made from a material whose Young’s modulus of Elasticity equals

Y .

When this rod is heated by temperature T and simultaneously subjected to a net longutudinal compressional force F, its length remains unchanged. The coefficient of volume expansion, of the material of the rod, is (nearly) equal to:

MEDIUM

General Science>Physics>Heat and Thermodynamics>Change of State

The pressure that has to be applied to the ends of a steel wire of length

10 cm

to keep its length constant when its temperature is raised by

100 ° C

is :
(For steel, Young's modulus is

2 \times 10^{11} N m^{- 2}

and coefficient of thermal expansion is

1.1 \times 10^{- 5} K^{- 1}

)

EASY

General Science>Physics>Heat and Thermodynamics>Change of State

A copper rod of

88 c m

and an aluminum rod of unknown length have their increase in length independent of increase in temperature. The length of aluminum rod is

(α_{C u} = 1.7 \times 10^{- 5} K^{- 1} a n d α_{Al} = 2.2 \times 10^{- 5} K^{- 1})

MEDIUM

General Science>Physics>Heat and Thermodynamics>Change of State

A solid expands upon heating because-

EASY

General Science>Physics>Heat and Thermodynamics>Change of State

A Bakelite beaker has volume capacity of

500 cc

30 ° C

. When it is partially filled with

V_{m}

volume (at

30 ° C

) of mercury, it is found that the unfilled volume of the beaker remains constant as temperature is varied. If

γ_{beaker} = 6 \times 10^{- 6} ° C^{- 1}, γ_{mercury} = 1.5 \times 10^{- 4} ° C^{- 1},

where

γ

is the coefficient of volume expansion, then

V_{m}

(in

cc

) is close to

EASY

General Science>Physics>Heat and Thermodynamics>Change of State

Thermal expansion of a solid is due to the

MEDIUM

General Science>Physics>Heat and Thermodynamics>Change of State

A compressive force,

F

is applied at the two ends of a long thin steel rod. It is heated, simultaneously, such that its temperature increases by

Δ T

. The net change in its length is zero. Let

l

be the length of the rod, A its area of cross-section,

Y

its Young's modulus, and

α

its coefficient of linear expansion. Then,

F

is equal to:

HARD

General Science>Physics>Heat and Thermodynamics>Change of State

40 ° C,

a brass wire of

1 m m

radius is hung from the ceiling. A small mass,

M

is hung from the free end of the wire. When the wire is cooled down from

40 ° C

20 ° C

it regains its original length of

0.2 m .

The value of

M

is close to:
(Coefficient of linear expansion and Young’s modulus of brass are

10^{- 5} /^{°} C

and

10^{11} N / m^{2},

respectively;

g = 10 m s^{- 2}

)

HARD

General Science>Physics>Heat and Thermodynamics>Change of State

The ends Q and R of two thin wires, PQ and RS, are soldered (joined) together. Initially each of the wires has a length of

1 m

10 ° C .

Now the end P is maintained at

10 ° C,

while the end S is heated and maintained at

400 ° C .

The system is thermally insulated from its surroundings. If the thermal conductivity of wire PQ is twice that of the wire RS and the coefficient of linear thermal expansion of PQ is

1.2 \times 10^{- 5} K^{- 1},

the change in length of the wire PQ is

HARD

General Science>Physics>Heat and Thermodynamics>Change of State

A leak proof cylinder of length

1 m,

made of a metal which has very low coefficient of expansion is floating vertically in water at

0^{o} C

such that its height above the water surface is

20 c m .

When the temperature of water is increased to

4^{o} C,

the height of the cylinder above the water surface becomes

21 c m .

The density of water at

T = 4^{o} C,

relative to the density at

T = 0^{o} C

is close to:

MEDIUM

General Science>Physics>Heat and Thermodynamics>Change of State

A non-isotropic solid metal cube has coefficients of linear expansion as:

5 \times 10^{- 5} /^{o} C

along the x-axis and

5 \times 10^{- 6} /^{o} C

along the y and the z-axis. If the coefficient of volume expansion of the solid is

C \times 10^{- 6} /^{o} C

, then the value of

C

is _____________

MEDIUM

General Science>Physics>Heat and Thermodynamics>Change of State

When the temperature of a metal wire is increased from $0 º C to 10 º C$ , its length increases by $0.02 %$ .The percentage change in its mass density will be closed to:

EASY

General Science>Physics>Heat and Thermodynamics>Change of State

Two rods of different materials having coefficients of linear expansion

α_{1}, α_{2}

and Young's modulii

Y_{1}

and

Y_{2}

respectively are fixed between two rigid massive walls. The rods are heated such that they undergo the same increase in temperature. There is no bending of rods. If

α_{1} : α_{2} = 2 : 3

, the thermal stresses developed in the two rods are equally provided

Y_{1} : Y_{2}

is equal to

EASY

General Science>Physics>Heat and Thermodynamics>Change of State

Two different wires having lengths

L_{1}

and

L_{2}

and respective temperature coefficient of linear expansion

α_{1}

and

α_{2},

are joined end-to-end. Then the effective temperature coefficient of linear expansion is :

EASY

General Science>Physics>Heat and Thermodynamics>Change of State

A horizontal steel railroad track has a length of

100 m

when the temperature is

25 ° C .

The track is constrained from expanding or bending. The stress on the track on a hot summer day, when the temperature is

40 ° C,

is (Note: The linear coefficient of thermal expansion for steel is

1.1 \times 10^{- 5} / {}^{\circ}C

and the Young's modulus of steel is

(2 \times 10^{11} Pa)

EASY

General Science>Physics>Heat and Thermodynamics>Change of State

The value of coefficient of volume expansion of glycerin is

5 \times 10^{- 4} K^{- 1}

. The magnitude of fractional change in the density of glycerin for a rise of

40^{o} C

in its temperature is:

EASY

General Science>Physics>Heat and Thermodynamics>Change of State

Coefficient of linear expansion of brass and steel rods are

α_{1}

and

α_{2}

. Lengths of brass and steel rods are

l_{1}

and

l_{2}

, respectively. If

(l_{2} - l_{1})

is maintained the same at all temperatures, which one of the following relations holds good?

When vapour condenses into liquid

Important Questions on Heat and Thermodynamics

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