Heat Introduction and Classification Questions

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Very Short Answers Questions [1 Mark Questions]

Ques. The Sun is the source of _______.

1. Only heat
2. Only light
3. Both heat and light
4. None of the above

Ans. The correct answer is c. Both heat and light

Explanation: The sun, like other stars, is mainly composed of hydrogen. It generates energy through nuclear fusion processes that convert hydrogen to helium. This fusion reaction within the sun produces a large amount of energy in the form of heat and light.

Ques. Temperature is the measure of the ______ of the body.

1. Coldness
2. Hotness
3. Hotness or coldness
4. None of the above

Ans. The correct answer is c. Hotness or coldness

Explanation: The temperature is determined by the degree of hotness or coldness of a body.

Ques. In which among the following processes does solid tend to get converted to vapors?

1. Melting
2. Sublimation
3. Heating
4. Breaking

Ans. The correct answer is b. Sublimation

Explanation: Solids are converted to vapors during the sublimation process.

Ques. The method in which the transfer of heat takes place by electromagnetic waves is

1. Convention
2. Conduction
3. Radiation
4. None of the above

Ans. The correct answer is c. Radiation

Explanation: Heat is transferred by electromagnetic waves through the process of radiation.

Ques. Heat can be converted to another form of energy.

1. True
2. False

Ans. The correct answer is a. True

Explanation: Heat energy can be converted into various types of energy. Heat energy is converted into electrical energy in thermal stations. Heat energy is converted to mechanical energy during the cooking process.

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Short Answers Questions [2 Marks Questions]

Ques. What is Heat?

Ans. Heat is a form of energy that flows when there is a difference in temperature between two bodies and produces a sense of warmth. Heat energy may be converted into other types of energy such as kinetic energy, mechanical energy, and so on.

Ques. Why does the heat energy flow from a higher-temperature substance to a lower-temperature substance?

Ans. In higher-temperature substances, molecules vibrate faster and transmit their energy to molecules vibrating slower in lower-temperature substances.

Ques. What is temperature?

Ans. The measurement of the hotness and coldness of a body is known as temperature. It is generally a measure of the kinetic energy of particles in an object, which indicates that particles present in the object are always moving.

Ques. What is the difference between an equilibrium state and a steady state?

Ans. An equilibrium state is one in which the characteristics are uniform throughout and do not change over time. A steady state is defined as the absence of change in characteristics at a certain place or location across time.

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Long Answers Questions [3 Marks Questions]

Ques. Calculate the specific latent heat of fusion of a solid if 25 g of it requires 8400 J of heat energy for melting.

Ans. Given

• Mass of the solid = 25 grams
• The energy required for melting = 8400 J

The amount of heat energy required to melt one unit mass of a material is known as the latent heat of fusion.

Here, unit mass = 1 gram

Therefore, the specific latent heat of fusion = 8400/25 = 336 J/g

In SI units, specific heat is calculated as J/kg

Therefore, the heat energy required to melt 1 kg mass completely is given by

Q = 336 x 1000 = 3.36 x 10⁵ J/kg

Specific heat = 3.36 x 10⁵ J/kg

Ques. What is the difference between heat and temperature?

Ans. The difference between heat and temperature is

Ques. Calculate the specific latent heat of fusion of a solid if 50 g of it requires 6300 J of heat energy for melting.

Ans. Given

• Mass of the solid = 50 grams
• The energy required for melting = 6300 J

The amount of heat energy required to melt one unit mass of a material is known as the latent heat of fusion.

Here, unit mass = 1 gram

Therefore, the specific latent heat of fusion = 6300/50 = 126 J/g

In SI units, specific heat is calculated as J/kg

Therefore, the heat energy required to melt 1 kg mass completely is given by

Q = 126 x 1000 = 1.26 x 10⁵ J/kg

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Very Long Answers Questions [5 Marks Questions]

Ques. Explain three methods of transfer of heat.

Ans. The three methods of heat transfer are

• Conduction: Heat conduction is the process by which heat is transmitted from the hotter to the cooler parts of a body without any real movement of the body's molecules. For example, when frying vegetables in a hot pan, heat is transferred from the flame to the pan, and then to the vegetables.
• Convection: Heat is transferred in the liquids and gases from a higher temperature zone to a lower temperature region during this process. Transfer of heat through convection is caused due to the movement of molecules or by mass transfer. For example, Heating of milk in a milk bowl.
• Radiation: It is the process through which heat is transmitted from one body to another without interacting with the molecules of the medium. Heat transfer through this process does not depend on the intervening medium. For example, heat energy is transferred from the sun to the earth by radiation.

Ques. The specific heat capacity of a metal is 160 J kg^-1K^-1. Calculate the amount of heat energy required to raise the temperature of 500 grams of the metal from 125 ℃ to 325 ℃.

Ans. Given

• Specific heat capacity of metal, C = 160 J kg^-1K^-1
• Mass of the metal, m = 500 grams = 500 x 10^-3 kg
• Final temperature, T₂ = 325 ℃ = 325 + 273 = 598 K
• Initial temperature, T₁ = 125 ℃ = 125 + 273 = 398 K

The formula for specific heat capacity is given by

C = Q / (m x ΔT)

⇒ Q = C x m x ΔT

Where

• Q is the amount of heat
• ΔT is the change in temperature

Change in temperature, ΔT = T₂ - T₁

⇒ ΔT = 598 - 398 = 200 K

On substituting the values, we get

Q = 160 x 500 x 10^-3 x 200

⇒ Q = 16000 J

Hence, the amount of heat required is 16000 J.

Ques. State the melting point, boiling point, specific heat capacity, specific latent heat of fusion, and specific latent heat of vaporization of water.

Ans. The definition of the given term is stated below

• Melting point: A material's melting point is the temperature at which it transitions from solid to liquid under air circumstances. At the melting point, the two states of matter, solid and liquid, are in balance. In the case of water, the melting point is 273 K, or 0 degrees Celsius.
• Boiling point: The boiling point of a liquid is the temperature at which the vapor pressure of the liquid equals the pressure of the surroundings, causing the liquid to change into a vapor. At boiling point, the vapor and liquid forms are in balance. In the case of water, the boiling point is 100 degrees Celsius, or 373 K. The standard boiling point is the temperature at which boiling happens at 1 bar of pressure, whereas the normal boiling point is the temperature at which boiling occurs at 1 atm of pressure.
• Specific heat capacity: The specific heat capacity of a material is the amount of energy required to raise the temperature of one kilogram of the substance by one degree Celsius.
• Specific latent heat of fusion: The heat energy needed to convert 1 kg of water from ice to liquid without changing its temperature is known as the specific latent heat of the fusion of water.
• Specific latent heat of vaporization: The heat energy required to convert 1 kg of water from liquid to vapor without affecting its temperature is known as the specific latent heat of vapourization of water.

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