Heat and Transfer MCQ Quiz - Objective Question with Answer for Heat and Transfer - Download Free PDF

Key Points

• Gold melts at an exact temperature of 1064°C, which is equivalent to 1947.52°F.
• This temperature is considered the melting point of gold, where it transitions from a solid to a liquid state.
• The melting point of gold is a critical property in various industries such as jewelry making, electronics, and manufacturing.
• Gold's high melting point signifies its ability to remain stable under high temperatures, making it suitable for industrial and scientific applications.

Additional Information

• Melting Point:
  • The melting point is the temperature at which a solid substance turns into a liquid.
  • For pure substances like gold, the melting point is a fixed and precise temperature.
  • It is an important physical property used to identify and characterize substances.
• Gold (Au):
  • Gold is a chemical element with the symbol Au and atomic number 79.
  • It is highly valued for its rarity, malleability, conductivity, and resistance to tarnish or corrosion.
  • Gold has been used historically in jewelry, currency, and as an investment asset.
• Applications of Gold's Melting Point:
  • In jewelry making, gold is often melted and cast into desired shapes.
  • In electronics, gold's melting point is crucial for soldering and creating precise connections.
  • In scientific research, gold is used in experiments that require materials resistant to high temperatures.
• Comparisons with Other Metals:
  • Gold's melting point is lower than that of metals like iron (1538°C) and platinum (1768°C), but higher than metals like lead (327°C).
  • This makes it easier to work with gold in manufacturing processes compared to some other metals.

The correct answer is Ironing clothes.

Key Points

• Conduction is the process of heat transfer through direct contact between materials.
• When ironing clothes, heat is transferred from the hot iron to the fabric through direct contact, exemplifying conduction.
• This process relies on the thermal conductivity of the materials involved, such as the metal surface of the iron and the fabric of the clothes.
• Conduction is most effective in solids where particles are closely packed and can transfer energy efficiently by vibrating against each other.

Additional Information

• Convection
  • Convection is the transfer of heat through the movement of fluids (liquids or gases).
  • Examples include boiling water where heat is transferred through the movement of water molecules.
  • It occurs because of the fluid's tendency to expand and rise when heated, creating a convection current.
• Radiation
  • Radiation is the transfer of heat through electromagnetic waves without involving particles.
  • The Sun heating the Earth is a prime example of radiation.
  • It does not require a medium and can occur in a vacuum.
• Thermal Conductivity
  • Thermal conductivity is a property of a material that indicates its ability to conduct heat.
  • Metals have high thermal conductivity, making them effective conductors of heat.
  • Materials with low thermal conductivity, like wood and plastic, are used as insulators.
• Heat Transfer
  • Heat transfer is the process of heat energy moving from a hotter object to a cooler one.
  • It can occur through conduction, convection, or radiation.
  • Understanding heat transfer is crucial in various applications, from industrial processes to everyday activities like cooking and heating homes.

The Correct answer is Radiation.

Key Points

• Radiation is the method of heat transfer that does not require a medium.
• It involves the transfer of heat through electromagnetic waves, such as infrared radiation.
• Heat transfer through radiation can occur in a vacuum, such as the transfer of heat from the Sun to Earth.
• Examples include the heat we feel from the Sun or a campfire, even though there is no direct contact or material medium.
• Radiation is governed by the laws of electromagnetic theory, specifically Planck’s Law, Stefan-Boltzmann Law, and Kirchhoff’s Law.
• Radiative heat transfer is used in applications such as solar panels, thermal imaging, and infrared heaters.

Additional Information

• Convection
  • Convection is the transfer of heat through the movement of fluids (liquids or gases).
  • It requires a medium for heat transfer, as it depends on the physical movement of particles within the fluid.
  • Examples include the heating of water in a pot or the circulation of air in an air conditioning system.
  • Convection plays a major role in natural phenomena such as ocean currents, atmospheric circulation, and mantle convection within the Earth.
• Conduction
  • Conduction involves the transfer of heat through direct contact between molecules.
  • It occurs in solids, liquids, and gases but is most effective in solids due to tightly packed molecules.
  • Examples include heat transfer through a metal rod or a cooking pan.
  • Conduction is governed by Fourier’s Law of heat conduction.
• Evaporation
  • Evaporation is the process where liquid molecules gain enough energy to escape into the vapor phase.
  • While it is not a primary method of heat transfer, it involves the transfer of energy during the phase change of a substance.
  • Examples include the cooling effect felt when sweat evaporates from the skin or water drying from a wet surface.
  • It plays an important role in processes such as water cycle and refrigeration systems.

The correct answer is Option 1: Both Assertion and Reason are correct, and Reason is the correct explanation for Assertion..

Key Points

• Metal pans are used for cooking because they are excellent conductors of heat, allowing heat to distribute evenly across the cooking surface.
• The high thermal conductivity of metals like aluminum, copper, and stainless steel helps in efficient cooking by transferring heat quickly from the stove to the food.
• Using metal pans ensures that food is cooked uniformly, preventing hotspots and reducing cooking times.
• The reason provided aligns with the assertion as it explains how the good heat-conducting property of metal pans facilitates quick and efficient cooking.

Additional Information

• Thermal Conductivity: The measure of a material's ability to conduct heat. Metals like copper and aluminum have high thermal conductivity, making them ideal for cooking utensils.
• Heat Distribution: Even heat distribution is crucial in cooking to ensure that food cooks uniformly without burning or undercooking in certain spots.
• Stainless Steel: Often used in cookware, it combines durability and resistance to rust, although it is less conductive than copper or aluminum.
• Heat Transfer Mechanism: Heat transfer in cooking occurs through conduction, convection, and radiation, with conduction being the primary method in metal pans.

The correct answer is Evaporation.

Important Points

• Evaporation
  • The process of conversion of a liquid into its vapors at room temperature is called evaporation.
  • The temperature at which the water starts evaporating is known as latent heat of vaporization.
• ​Sublimation
  • It is a process of conversion of a solid into vapor without passing through the liquid state.
  • Examples of sublimes are Iodine, Camphor, etc.
• Condensation
  • ​It is the process of conversion of the gas phase into the liquid phase.
  • Condensation is caused by the loss of heat.

Key Points

• An earthen pitcher used in summer cools water in it essentially by evaporation of water from its porous surface.
• The walls of an earthen pot are porous, which leads to seepage of water and evaporates from the surface of the pot.
• The heat required for evaporation is taken from the water inside the pot, thus cooling the water stored inside. This is the reason why water remains cool in the earthen pot even on hot summer days

The correct answer is Element.

Important Points

• The coil of an electric room heater is termed as an element.
  • The heating coil of the electric room heater transfers the electric energy into heat energy.
  • The coil of the electric heater is made up of nichrome.
  • Nichrome consists of 80% nickel, 20% chromium.
• In an incandescent bulb, an electric current is passed through a metal filament.

The correct answer is Convection.

Key Points

• Water in an electric kettle becomes hot by convection. It is the process of transfer of heat by mass motion of a fluid such as water when the heated fluid is caused to move away from the source of it and carrying energy with it.
• Conduction is the process of transmission of heat through the material of a substance.
• Radiation is the process of emission of energy in the form of moving subatomic particles or electromagnetic waves.

Explanation:

The movement of energy from one place to another is called energy transfer. Heat transfer mainly takes place due to temperature differences.

There are three modes of Heat transfer.

Conduction: 

• The mode of heat transfer in solids where heat transfer takes place without the movement of medium particles is called conduction.
• For example, by heating one end of a metal rod we can feel the heat at the other end.

Convection: 

• The mode of heat transfer in fluids where heat transfer takes place due to the movement of particles of the medium is called convection.
• For example, the heating of water in a pot.

Radiation: 

• The mode of heat transfer where heat is transferred from one place to another without affecting the medium particles is called radiation.
• The given diagram shows the way in which all three modes of heat transfer works.

The correct answer is Convection.

Key Points

• Convection is a mode of heat transfer by the actual motion of matter.
• Convection is a process in which hot, less dense materials rise upward and are replaced by colder, more dense materials.
• Convection is possible only in fluids.
• Convection can be either be natural or forced.
• Gravity plays a major role in natural convection.
• Material is forced to move by a pump or by some other physical means in forced convection.
• Forced-air heating systems in the home, the human circulatory system are the common examples of forced convection.

Additional Information

• The three distinct modes of heat transfer are:
  1. Conduction.
  2. Convection.
  3. Radiation.
• The process of heat transfer without any medium is called radiation.
• Conduction is the process of heat transfer between two adjacent parts of a body due to their temperature difference.
• Condensation is the process where water vapor becomes liquid.

The correct answer is White surface reflects more heat energy and absorbs less heat energy.

Key Points

• A white surface reflects more heat energy and absorbs less heat energy this is the reason the top and outer surfaces of the house are painted white.
• White color is a poor emitter of heat.
• Hence, white-colored clothes are preferred in summer.

Additional Information

• The black color is a good absorber and a better emitter of heat.
• Hence, the inner side of the solar cooker is painted black
• Transfer of it takes place in three ways conduction, convection, and radiation.

CONCEPT: 

• When an electric current is passed through a conductor, the conductor becomes hot after some time and produce heat.
• This happens due to the conversion of some electric energy passing through the conductor into heat energy.  This effect of electric current is called the heating effect of the current or Joule heating effect.
• The appliances based on the heating effect of electric current work on both AC and DC supply.
• The amount of heat liberated can be given as 
• \(H = \frac{{Pt}}{{4.2}}cal \Rightarrow \;H = W = \;Pt = {I^2}R\;joule\)

Electric current passing through conductor = IT

The power dissipated across copper coil = P

Work done by current = W

The resistance of wire = R

Heat dissipated because of current = H

time period = t

CALCULATION:

Given data

⇒ The resistance of a coil = 418 ohms

⇒ Amount of time the current is passed = 1 × 60 = 60 sec

⇒ Current Passed = 0.3 A

→ As 

H = I²RT where,

H = Heat Generated in Joules

I = Current in Amperes

R = Resistance of coil in Ohms

T = time in seconds

→ H = (0.3)² × 418 × 60

= 2257.2 joules

→ 1 calorie = 4.184 joules or

4.184 joules = 1 calorie

1 Joules = 1 / 4.184 calorie

2257.2 joules = (1 / 4.184) × 2257.2 calorie

= 539.48 ≅ 540 calorie

The correct answer is Radiation.

Key Points

• There are three modes of transmission of heat:-Conduction, Convection, and Radiation.

1. Conduction
   • In this mode of transmission, heat dissipates from one place to another by molecular vibration.
   • Conduction needs a medium to transfer heat.
   • It is relevant to solid only.
2. Convection
   • Heat is transferred from one place to another by the transfer of molecules.
   • It happens only in liquids or gases.
   • It also needs a medium to transfer heat.
3. Radiation
   • It transfers heat in the form of electromagnetic waves.
   • It can heat any form of material.
   • It doesn't need any medium for the transfer of heat.

Important Points

• Radiation travels with the speed of light. So the rate of heat transfer is maximum in radiation in the form of electromagnetic radiation.

The correct answer is Latent heat of fusion.

Key Points

• Latent heat of Fusion:
  • It is defined as the amount of heat energy that is required to change 1 kg of a solid into liquid at atmospheric pressure at its melting point. Or
  • The amount of heat required per unit mass of a substance at the melting point to convert it from the solid to the liquid state is called the latent heat of fusion of solid.
  • Its unit is cal/gram.
  • Example: Latent heat of fusion of ice
    • The amount of heat required to convert per unit mass of the ice into the water at 0°C temperature is called the latent heat of fusion of ice.
    • Latent heat of fusion of ice (L) = 80 cal/gram

Additional Information

• Latent heat of vaporization of liquid:
  • The amount of heat required to vaporize a unit mass of liquid at its boiling point is called the latent heat of vaporization.
  • Example: Latent heat of vaporization of water or latent heat of steam
    • The amount of heat required to convert into the steam of a unit mass of water at its boiling point (100°C) is called the latent heat of vaporization of water or latent heat of steam.
    • Latent heat of steam(L) = 540 cal/gram
• ​Latent heat of condensation:
  • The conversion of water vapour into the water is caused by the loss of heat called Latent heat condensation.
  • Condensation depends upon the amount of cooling and the relative humidity of the air.
• Latent heat of sublimation:​​
  • The amount of heat required to convert the unit mass of the solid to vapour is called the latent heat of sublimation. ​
  • When a solid is heated at a constant pressure, which is lower than that of the triple point, it does not melt but gives of its vapour directly, this process is known as sublimation.
  • The system consists of two phases, the solid and the vapour.
  • The resulting two-phase system behaves essentially identically with the other two types of two-phase systems.
  • The intensive state of the system has one degree of freedom.
  • The process of sublimation at constant pressure and temperature, like the process of melting or evaporation, requires the addition of the latent heat of sublimation.

The correct answer is 12.5 J/s.

Concept:

• According to Fourier’s law, the rate of heat flow, Q through a homogeneous solid is directly proportional to the area A, of the section at the right angles to the direction of the heat flow, and to the temperature difference dT along the path of heat flow.

Q = - KA dT/dX

Given:

• Rate of Heat loss = K = 0.15
• Temp Difference = dT = 25 - 5 = 20 C
• dX = 24 cm = 0.24 m
• Area (asked for per metre square) = 1 m2

Explaination:-

• Q = - KA dT/dX
• = 0.15 x 1 x 20 / 0.24
• = 12.5 J/s

The correct answer is Latent Heat.

Concept:

• Latent Heat - It is the heat required to convert a solid into a liquid or vapour, or a liquid into a vapour, without a change of temperature.
• English scientific expert Joseph Black presented the idea of latent heat.

Important Points

• The specific heat is the amount of heat per unit mass required to raise the temperature by one degree Celsius. 
• The specific heat of water is 1 calorie/gram °C = 4.186 joule/gram °C, which is higher than many other common substances.