Tag: heat, internal energy and work

Questions Related to heat, internal energy and work

Define the term heat :

physics heat energy transfers heat energy heat, internal energy and work internal energy

  1. the condition or quality of being hot

  2. the sensation of warmth or hotness

  3. the degree of hotness; temperature

  4. all of the above

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Correct Option: D
Explanation:

Heat is the transfer of kinetic energy from one medium or object to another. Such energy transfer can occur in three ways: radiation, conduction, and convection.

Also, it can be defined as the quality of being hot, high temperature, and degree of hotness and temperature.

In a sports meet the timing of a $200\ m$ straight dash is recorded at the finish point by starting an accurate stop watch on hearing the sound of starting gun fired at the starting point. The time recorded will be more accurate

physics heat energy transfers heat energy heat, internal energy and work internal energy

  1. In winter

  2. In summer

  3. In all seasons

  4. None of these

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Correct Option: B
Explanation:

The velocity of sound is directly proportional to the square root of absolute temperature.
The formula for velocity of sound in a gas is
$v = \sqrt {\dfrac {\gamma p}{\rho}}$
According to standard gas equation
$pV = RT$
or $p = \dfrac {RT}{V}$
$\therefore v = \sqrt {\dfrac {\gamma RT}{\rho \times V}} = \sqrt {\dfrac {\gamma RT}{M}}$
where $\rho \times V = M$, the molecular weight of the gas
$\therefore v\propto \sqrt {T}$
Hence, the sound of the gun fired at the starting point will reach the finishing point quicker in summer than in winter. The lapse of time due to the time taken by the sound in reaching the finish point will be less in summer and, hence the time recorded will be more accurate in summer than in winter.

Two blocks of steel A and B of the same shape and size, A being two times heavier than B, are at $40^{\circ}C$. The ratio of heat content of A to B is

physics heat energy transfers heat energy heat, internal energy and work internal energy

  1. $1$

  2. $4$

  3. $2$

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

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Correct Option: C
Explanation:

The correct answer is option(C).

We know,
$Q=mC\Delta T$
Here Specific heat and raise in temperatures are equal.
And, given $2m _A=m _B$
So, the ratio of heat content can be,
$\dfrac {Q _1}{Q _2}=\dfrac {m _AC\Delta T}{m _BC\Delta T}=\dfrac {m _A}{m _B}=\dfrac 21=2$

State whether given statement is True or False
Heat is an invisible form of energy, which causes the sensation of hotness or coldness.

physics heat energy transfers heat energy heat, internal energy and work internal energy

  1. True

  2. False

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Correct Option: A
Explanation:

No body can see the exchange of heat or heat itself it is invisible and its effect or transfer can only be felt by the increases or decreases in temperature or the sensation of hotness and coldness.
Hence, OPTION : A (true).

According to law of conservation of energy, heat energy is transformed into which two types of energy?

physics heat energy transfers heat energy heat, internal energy and work internal energy

  1. Kinetic and potential energy

  2. Mechanical and potential energy

  3. Kinetic and thermal energy

  4. Nuclear and potential energy

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Correct Option: A
Explanation:

According to law of conservation of energy, heat energy is transformed into Kinetic and potential energy

State whether the given statement is True or False
The boiling point of liquid increases with increase in pressure.

physics the kinetic model of matter evaporation heat, internal energy and work phase change

  1. True

  2. False

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Correct Option: A
Explanation:

The rate of evaporation  increase with a decrease in the gas pressure around a liquid. Molecules like to move from areas of higher pressure to lower pressure

Rate of evaporation increases 

physics the kinetic model of matter evaporation heat, internal energy and work phase change

  1. with the rise in temperature

  2. with the fall in temperature

  3. irrespective of temperature

  4. only beyond room temperature

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Correct Option: A
Explanation:

Rate of evaporation Increases with the rise in temperature as increasing temperature increases the kinetic energy of molecules of the liquid which facilitates the molecule to convert into vapour.

Water evaporates under atmospheric pressure. Without changing the temperature, the same water is placed under partial vacuum. The rate of evaporation _________.

physics the kinetic model of matter evaporation heat, internal energy and work phase change

  1. increases

  2. drop to zero

  3. decreases

  4. remain unaffected

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Correct Option: A
Explanation:
In partial pressure, the pressure is less;
According to Le-chatlier's principle on decreasing pressure; volume increases, so more water into gas(vapour)
So, rate of evaporation increases.

When the temperature of water rises, the rate of evaporation

physics the kinetic model of matter evaporation heat, internal energy and work phase change

  1. increases

  2. decreases

  3. remain the same

  4. first decrease then increases

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Correct Option: A
Explanation:

The higher the temperature of the substance the greater the kinetic energy of the molecules at its surface and therefore the faster the rate of their evaporation.

One of the most common phenomenon related to rainfall is

physics the kinetic model of matter evaporation heat, internal energy and work phase change

  1. Evaporation

  2. Vaporization

  3. Fusion

  4. Solidification

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Correct Option: A
Explanation:

Rainfall occurs primarily due to evaporation of water from water bodies like lakes and oceans and condensation of water in the form of precipitation like rainfall or snowfall.