Thermal Properties of Matter

Thermal Properties of Matter

Moderate Questions
Difficult Questions

Thermal Physics

Thermal Properties of Matter
Thermodynamics
Kinetic Theory
  1. The two ends of a metal rod are maintained at temperatures 100°C and 110°C. The rate of heat flow in the rod is found to be 4.0 J/s. If the ends are maintained at temperatures 200°C and 210°C, the rate of heat flow will be








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    As the temperature difference ∆T = 10°C as well as the thermal resistance is same for both the cases, so thermal current or rate of heat flow will also be same for both the cases.

    Correct Option: C

    As the temperature difference ∆T = 10°C as well as the thermal resistance is same for both the cases, so thermal current or rate of heat flow will also be same for both the cases.

  1. Steam at 100°C is passed into 20 g of water at 10°C. When water acquires a temperature of 80°C, the mass of water present will be:
    [Take specific heat of water = 1 cal g–1 °C–1 and latent heat of steam = 540 cal g–1]








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    According to the principle of calorimetry.
    Heat lost = Heat gained
    mLv + msw∆θ = mwswΔ θ
    ⇒ m × 540 + m × 1 × (100 – 80)
    = 20 × 1 × (80 – 10)
    ⇒ m = 2.5 g
    Therefore total mass of water at 80°C
    = (20 + 2.5) g = 22.5 g

    Correct Option: D

    According to the principle of calorimetry.
    Heat lost = Heat gained
    mLv + msw∆θ = mwswΔ θ
    ⇒ m × 540 + m × 1 × (100 – 80)
    = 20 × 1 × (80 – 10)
    ⇒ m = 2.5 g
    Therefore total mass of water at 80°C
    = (20 + 2.5) g = 22.5 g

  1. A piece of iron is heated in a flame. It first becomes dull red then becomes reddish yellow and finally turns to white hot. The correct explanation for the above observation is possible by using








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    Wein’s displacement law
    According to this law
    λmax ∝ 1/T
    or, λmax × T = constant
    So, as the temperature increases λ decreases.

    Correct Option: A

    Wein’s displacement law
    According to this law
    λmax ∝ 1/T
    or, λmax × T = constant
    So, as the temperature increases λ decreases.

  1. Two metal rods 1 and 2 of same lengths have same temperature difference between their ends. Their thermal conductivities are K1 and K2 and cross sectional areas A1 and A2, respectively. If the rate of heat conduction in rod 1 is four times that in rod 2, then








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    Q1 = 4Q2 (Given)

    ⇒
    K1A1Δt
    		 = 4
    K2A2Δt
    		 ⇒ K1A1 = 4K2A2
    LL

    Q = σeAT4

    Correct Option: B

    Q1 = 4Q2 (Given)

    ⇒
    K1A1Δt
    		 = 4
    K2A2Δt
    		 ⇒ K1A1 = 4K2A2
    LL

    Q = σeAT4

  1. A body cools from 50.0°C to 48°C in 5s. How long will it take to cool from 40.0°C to 39°C? Assume the temperature of surroundings to be 30.0°C and Newton's law of cooling to be valid.








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    Rate of cooling ∝ temperature difference
    between system and surrounding.
    As the temperature difference is halved, so the rate of cooling will also be halved.
    So time taken will be doubled
    t = 2 × 5 sec. = 10 sec.

    Correct Option: B

    Rate of cooling ∝ temperature difference
    between system and surrounding.
    As the temperature difference is halved, so the rate of cooling will also be halved.
    So time taken will be doubled
    t = 2 × 5 sec. = 10 sec.