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All questions of Thermal Properties of Matter for JEE Exam

5 g of ice at 0° C is mixed with 10 g of water at 10° C. The temperature of the mixture is:
  • a)
    2°C
  • b)
    0°C​
  • c)
    5°C
  • d)
    2.5°C
Correct answer is option 'B'. Can you explain this answer?

Riya Banerjee answered
Heat absorbed by 5g ice when it converted to at 0° C = 5 x 80 = 400 cal.
Heat liberated by 10g water at 10° C to 0° C = 100 cal
Hence there is 15g water at 0° C and 300 cal needs to be liberated , thus for some amount of water converts into ice, hence the temp of mixture is 0° C.

Can you explain the answer of this question below:

Water is used as coolant in automobiles radiators because

  • A:

    it has high specific heat capacity

  • B:

    it is easily available

  • C:

    it is easy to carry

  • D:

    it is cheap

The answer is a.

Lavanya Menon answered
Water is used as a coolant in automobiles radiators because it has high specific heat capacity. So, it absorbs a large amount of heat for a degree rise in temperature.

When water is heated from 0° C to 20° C its volume:
  • a)
    first decreases and then increases
  • b)
    goes on increasing
  • c)
    remains constant up to 15°C and then increases
  • d)
    goes on decreasing
Correct answer is option 'A'. Can you explain this answer?

Pooja Shah answered
When water is heated from 0°C, its volume decreases because its density increases and you can see this effect upto 4°C. Since the density of ice is maximum at 4°C, afterwards as the density decreases the volume increases. The main reason for this is hydrogen bond in ice gets cleaved due to the melting of ice.

Newton’s law of cooling states that the rate of cooling of a body is proportional to the _____________________.
  • a)
    temperature of the surroundings
  • b)
    excess temperature of the body over the surroundings
  • c)
    temperature of the body
  • d)
    temperature of the body + temperature of the surroundings
Correct answer is option 'B'. Can you explain this answer?

Geetika Shah answered
Newton's law of cooling states that the heat released by a body with respect to time (or) the rate of heat released is directly proportional to the difference between the body's temperature and the surrounding temperature. 
dH/dt = k(T – Ts) where t = surrounding's temperature and T = temperature of the body 
Consider two bodies A and B, of equal surface areas, such that A's temperature is more that B's temperature and the surrounding temperature is less than both A and B. Then according to Newton's law of cooling A loses more heat to the surroundings when compared B during the same time interval. So, A will cool faster than B.

The temperature for which the reading on Celsius and Fahrenheit scales are identical is
  • a)
    -273°C, -273 °F
  • b)
    -30°C, -30 °F
  • c)
    0 °C, 0 °F
  • d)
    -40 °C, -40 °F
Correct answer is option 'D'. Can you explain this answer?

Preeti Iyer answered
The Celsius and Fahrenheit are two important temperature scales. The Fahrenheit scale is used primarily in the United States, while Celsius is used throughout the world. The two scales have different zero points and the Celsius degree is bigger than the Fahrenheit one. There is one point on the Fahrenheit and Celsius scales where the temperatures in degrees are equal. This is -40 degree C and -40 degree F.

What is the expression for temperature gradient?
  • a)
  • b)
  • c)
  • d)
Correct answer is option 'C'. Can you explain this answer?

Krishna Iyer answered
A temperature gradient is a physical quantity that describes in which direction and at what rate the temperature changes the most rapidly around a particular location.
The temperature gradient is a dimensional quantity expressed in units of degrees per unit length.
The SI unit is kelvin per meter.
Expression: ∆T/∆x, where ∆T = change in temperature and ∆x = change in distance

A piece of iron of mass 100g is kept inside a furnace for a long time and Jthen put in a calorimeter of water equivalent 10g containing 240g of water at 20°C. The mixture attains an equilibrium temperature of 60°C. Find the temperature of the furnace. Specific heat capacity of iron = 470J/kg-°C.
  • a)
    500°C
  • b)
    900°C
  • c)
    953.6C
  • d)
    706.80 °C
Correct answer is option 'C'. Can you explain this answer?

Gaurav Kumar answered
Mass of Iron = 100g
Water Eq of caloriemeter = 10g
Mass of water = 240g
Let the Temp. of surface = 0ºC
Siron = 470J/kg°C 
Total heat gained = Total heat lost.
So,100/1000× 470 × (θ – 60) = 250/1000 × 4200 × (60 – 20)
⇒ 47θ – 47 × 60 = 25 × 42 × 40
⇒  θ = 4200 + 2820/47= 44820/47 =953.61°C

Water contract on heating between the temperatures
  • a)
    0°C to 4°C
  • b)
    0°K to 4°K
  • c)
    0o K to 273 K
  • d)
    0°F to 4°F
Correct answer is option 'A'. Can you explain this answer?

Geetika Shah answered
When water is heated from 0oC, its volume decreases because its density increases and you can see this effect upto 4oC. Since the density of ice is maximum at 4oC, afterwards as the density decreases the volume increases. The main reason for this is hydrogen bond in ice gets cleaved due to the melting of ice.

The heat of sun comes to us through:
  • a)
    convection
  • b)
    conduction
  • c)
    Sublimation
  • d)
    Radiation
Correct answer is option 'D'. Can you explain this answer?

Om Desai answered
The sun heats the earth through radiation. Since there is no medium (like the gas in our atmosphere) in space, radiation is the primary way that heat travels in space. When the heat reaches the earth it warms the molecules of the atmosphere, and they warm other molecules and so on.

A device in which heat measurement can be made is called
  • a)
    Joule meter
  • b)
    Calorimeter
  • c)
    Thermal meter
  • d)
    Gauge meter
Correct answer is option 'B'. Can you explain this answer?

Shanaya Tiwari answered
Calorimeter:
The correct device for heat measurement is a calorimeter. Calorimeters are used to measure the heat involved in a chemical reaction or physical change. They work based on the principle of conservation of energy, where the heat released or absorbed during a reaction is measured by the change in temperature of a known mass of water.

How does a Calorimeter work?
- A known quantity of the substance undergoing the reaction is placed in the calorimeter along with a known quantity of water.
- The initial temperature of the water and the substance is recorded.
- The reaction takes place, and the heat released or absorbed causes a change in temperature of the water.
- By measuring the change in temperature, the heat exchanged can be calculated using the specific heat capacity of water.
- Calorimeters are designed to minimize heat loss to the surroundings to ensure accurate measurements.

Types of Calorimeters:
- There are different types of calorimeters such as bomb calorimeters, coffee cup calorimeters, and differential scanning calorimeters, each suitable for different applications.
- Bomb calorimeters are commonly used for measuring the heat of combustion of substances.
- Coffee cup calorimeters are simpler and are often used in educational settings to demonstrate heat exchange principles.
In conclusion, a calorimeter is the appropriate device for heat measurement as it allows for accurate determination of the heat involved in a reaction or process.

Can you explain the answer of this question below:

Two identical rectangular strips, one of copper and the other of steel, are riveted as shown to form a bi-metal strip. On heating, the bi-metal strip will

72601_ra1 (1)

  • A:

    bend with steel on the concave side

  • B:

    get twisted

  • C:

    remain straight

  • D:

    bend with steel on the convex side

The answer is a.

Nandini Patel answered
On heating, the copper strip will suffer greater elongation and hence the bimetal strip will bend with the steel strip on the concave side. 
[Bimetal strips are widely used in thermal switching applications such as automatic electric iron].

The process by which heat flows from the region of higher temperature to the region of lower temperature by actual movement of material particles is called
  • a)
    Sublimation
  • b)
    radiaton
  • c)
    Conduction
  • d)
    Convection
Correct answer is option 'D'. Can you explain this answer?

Rajat Patel answered
In this process, heat is transferred in the liquid and gases from a region of higher temperature to a region of lower temperature. Convection heat transfer occurs partly due to the actual movement of molecules or due to the mass transfer.

What is the coefficient of thermal conductivity K?
  • a)
    ΔQt
  • b)
  • c)
  • d)
Correct answer is option 'C'. Can you explain this answer?

Aryan Keshri answered
Every object has its own capacity to conduct heat.  To determine how much it is we use this term. Thermal conductivity (λ or k) is the capacity of the body to conduct or spread heat.

K=QL/AΔTt

Where,
thermal conductivity is k in W/m K,
the amount of heat transfer through the material is Q in J/S or W,
the area of the body is A in m2,
the difference in temperature is ΔT  in K.

Which of the given phenomenon is not related to convection?
  • a)
    In winter metallic handles appear colder than wooden door
  • b)
    Maintaining comfortable room temperature in cold countries
  • c)
    Formation of trade winds
  • d)
    Formation of land and sea breezes
Correct answer is option 'A'. Can you explain this answer?

Convection is the movement of surrounding medium according to density by which transfer of heat takes place. Whereas in option A it tells about the transfer of heat due to molecules inside conductor which is conduction

According to law of calorimetry, which of the given relation is true?
  • a)
    Heat gained ≥ Heat lost
  • b)
    Heat gained = Heat lost
  • c)
    Heat gained > Heat lost
  • d)
    Heat lost > Heat gained
Correct answer is option 'B'. Can you explain this answer?

Anjali Iyer answered
A principle of calorimetry states that if there is no loss of heat in surrounding the total heat lost by hot body equal to the total heat gained by a cold body.

i.e. heat loss = heat gain

Value of coefficient of thermal coefficient is:
  • a)
    same incase of conductors and insulators
  • b)
    Good incase of conductors and small incase of insulators
  • c)
    Does not depend on insulators and conductors
  • d)
    Small incase of insulators and good incase of insulators
Correct answer is option 'B'. Can you explain this answer?

Raghav Bansal answered
Conductors have free electrons in them whereas insulators don’t have any. Therefore, conductors conduct heat and electricity better than insulators. Therefore the value of thermal coefficient is good in case of conductors and less in case in insulators.

An increase in temperature in a liquid would cause a phase change to which of the following?
  • a)
    Gas
  • b)
    liquid
  • c)
    solid
  • d)
    plasma
Correct answer is option 'A'. Can you explain this answer?

Neha Sharma answered
Increasing the temperature of liquid, increases the average K.E. of the molecules. The molecules start moving vigorously in all the directions, thereby increasing and the inter-molecular space between them. Thus, the liquid changes into gas.

The temperature and pressure at which all three phases of a substances coexist is called
  • a)
    Fusion point
  • b)
    Triple point​
  • c)
    Sublimation point
  • d)
    Melting Point
Correct answer is option 'B'. Can you explain this answer?

Rajeev Saxena answered
In thermodynamics, the triple point of a substance is the temperature and pressure at which the three phases (gas, liquid, and solid) of that substance coexist in thermodynamic equilibrium. It is that temperature and pressure at which the sublimation curve, fusion curve and the vaporisation curve meet.

The mechanism of transfer of heat between two adjacent parts of a body because of their temperature difference is known as
  • a)
    conduction
  • b)
    convection
  • c)
    Sublimation
  • d)
    Fusion
Correct answer is option 'A'. Can you explain this answer?

Geetika Shah answered
The mechanism of transfer of heat between two adjacent parts of a body because of their temperature difference is known as conduction. This is the definition of conduction.

The relation between coefficient of volume expansion  and coefficient of linear expansion  is
  • a)
    αv = 2α1
  • b)
    α1 = 3αv
  • c)
    αv = 3α1
  • d)
    α1 = 2αv
Correct answer is option 'C'. Can you explain this answer?

Lavanya Menon answered
This is simple because the coefficients of linear expansion αL, areal expansion αA, and volume expansion αv, are in the ratio of 1: 2: 3 i.e.:
αL: αA: αv :: 1: 2: 3
Hence, αv = 3αL

When two light nuclei combine to form a heavier nucleus, process is said to be
  • a)
    nuclear fission
  • b)
    nuclear fusion
  • c)
    nuclear power
  • d)
    nuclear transmutation
Correct answer is option 'B'. Can you explain this answer?

Arun Khanna answered
This Process is called Nuclear Fussion.It is found in the sun. Nuclear fission is a reaction in which two small nuclei combine together to form a big nuclei and release energy. This type of reaction takes place in sun and is the reason behind the massive amount of energy it sun provides.

What happens to the volume of the substance when the temperature increases?
  • a)
    decreases
  • b)
    increases
  • c)
    remains same
  • d)
    not measurable
Correct answer is option 'B'. Can you explain this answer?

Rajat Patel answered
In general, liquids tend to get “thinner” when their temperature increases. In general, the liquids tend to expand when their temperature increases. For example, the same mass of boiling water occupies more volume at 100 degrees Celsius than at 20 degrees Celsius. Therefore, increasing temperature decreases density.

Which is the fastest mode of heat transfer?
  • a)
    convection
  • b)
    conduction
  • c)
    Transition
  • d)
    Radiation
Correct answer is option 'D'. Can you explain this answer?

Arun Khanna answered
Answer: Radiation is the fastest mode of transfer of heat, because radiation travels at the speed of light, which is very quick. The slowest mode of transfer of heat is conduction because it takes place from particle to particle.

Among the following methods of heat transfer, gravity does not play any part in
  • a)
    Convection
  • b)
    Radiation and conduction
  • c)
    radiation
  • d)
    convection and conduction
Correct answer is option 'B'. Can you explain this answer?

Rajat Patel answered
Gravity does not play any part in radiation and conduction because in both these processes heat is transferred without any motion of the medium particles.

What are units of K?
  • a)
    Wm-2K-1
  • b)
    WmK
  • c)
    Wm-1K-1
  • d)
    Wm-1K-2
Correct answer is option 'C'. Can you explain this answer?

Rishika Mishra answered
Understanding K
K, known as thermal conductivity, is a property of materials that indicates their ability to conduct heat. The units of K are crucial for understanding heat transfer.
Unit Analysis of Options
- Option A: Wm-2K-1
- This unit represents watts per square meter per Kelvin, typically used for heat transfer per unit area, not for thermal conductivity.
- Option B: WmK
- This unit suggests watts per meter Kelvin, which does not correctly express the relationship of heat transfer through a material.
- Option C: Wm-1K-1
- This is the correct unit for thermal conductivity. It represents watts per meter per Kelvin, indicating how much heat (in watts) can pass through a meter of the material for every degree of temperature difference (in Kelvin).
- Option D: Wm-1K-2
- This unit indicates watts per meter per Kelvin squared, which does not correspond to thermal conductivity and is not relevant in this context.
Conclusion
K = Wm-1K-1 signifies that for every meter of material, how effectively it conducts heat is measured against a temperature difference. Understanding this unit is essential for applications in engineering and physics, especially in thermal management and insulation design. Thus, option C is the correct answer for the units of K.

Four cylindrical rods of different radii and lengths are used to connect two heat reservoirs at fixed temperatures t1 and t2 respectively. From the following pick out the rod which will conduct the maximum quantity of heat:
  • a)
    Radius 1 cm, length 2 m
  • b)
    Radius 1 cm, length 1 m
  • c)
    Radius 2 cm, length 4 m
  • d)
    Radius 3 cm, length 8 m
Correct answer is option 'D'. Can you explain this answer?

Neha Sharma answered
The rate of heat transfer is directly proportional to the bisectional surface area of the solid and inversely proportional to its parallel length. 
That is heat conduction rate say H ∝ r2
∝ 1/L
I.e ∝ r2/L
Hence the conduction would be
maximum in case in which  r2/L ratio is largest.

SI unit of latent heat is
  • a)
    Cal/ Kg
  • b)
    J Kg
  • c)
    J Kg -2
  • d)
    J/Kg
Correct answer is option 'D'. Can you explain this answer?

Jyoti Dey answered
The correct answer is option 'D', J/Kg.

Latent heat is the amount of heat energy required or released during a phase change of a substance, such as melting or vaporization, at a constant temperature and pressure. It is a specific type of heat energy associated with the change in the internal energy of a substance, without a change in its temperature.

There are two types of latent heat: latent heat of fusion and latent heat of vaporization. The latent heat of fusion refers to the heat energy required to change a substance from a solid to a liquid state, while the latent heat of vaporization refers to the heat energy required to change a substance from a liquid to a gaseous state.

The SI unit of latent heat is Joule per kilogram (J/Kg). The Joule is the SI unit of energy, and the kilogram is the SI unit of mass. So, when we express the latent heat in the SI unit, we are essentially referring to the amount of energy required or released per unit mass of the substance during a phase change.

The SI unit of latent heat can be derived by considering the equation Q = mL, where Q is the heat energy required or released, m is the mass of the substance, and L is the latent heat. By rearranging the equation, we get L = Q/m. Since Q is in Joules and m is in kilograms, the SI unit of latent heat is J/Kg.

So, option 'D', J/Kg, is the correct answer for the SI unit of latent heat.

Which of the given relation is true for Newton’s law of cooling?
  • a)
  • b)
  • c)
  • d)
Correct answer is option 'D'. Can you explain this answer?

Arka Bose answered
Newton's law of cooling states that the heat released by a body with respect to time (or) the rate of heat released is directly proportional to the difference between the body's temperature and the surrounding temperature. 
dH/dt = k(T – Ts) where t = surrounding's temperature and T = temperature of the body 
Consider two bodies A and B, of equal surface areas, such that A's temperature is more that B's temperature and the surrounding temperature is less than both A and B. Then according to Newton's law of cooling A loses more heat to the surroundings when compared B during the same time interval. So, A will cool faster than B.

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