Thermal Properties of Matter

Thermal Properties of Matter

Moderate Questions
Difficult Questions

Thermal Physics

Thermal Properties of Matter
Thermodynamics
Kinetic Theory
  1. Radiation from which of the following sources, approximates black body radiation best?








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    NA

    Correct Option: D

    NA

  1. A black body has maximum wavelength λm at temperature 2000 K. Its corresponding wavelength at temperature 3000 K will be








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    According to Wein's displacement law,
    λmT = 2.88 × 10–3
    When T = 2000 K,
    λm (2000) = 2.88 × 10–3 ....(1)
    When T = 3000 K,
    λ'm (3000) = 2.88 × 10–3 ....(2)
    Dividing (1) by (2),

    2
    λm
    		 = 1 ⇒
    λm
    		 =
    3
    		 ⇒ λ'm =
    2
    		λm
    3λmλ'm23

    Correct Option: B

    According to Wein's displacement law,
    λmT = 2.88 × 10–3
    When T = 2000 K,
    λm (2000) = 2.88 × 10–3 ....(1)
    When T = 3000 K,
    λ'm (3000) = 2.88 × 10–3 ....(2)
    Dividing (1) by (2),

    2
    λm
    		 = 1 ⇒
    λm
    		 =
    3
    		 ⇒ λ'm =
    2
    		λm
    3λmλ'm23

  1. A cylindrical rod having temperature T1 and T2 at its end. The rate of flow of heat is Q1 cal/sec. If all the linear dimensions are doubled keeping temperature constant, then the rate of flow of heat Q2 will be








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    Q =
    KA(θ1 - θ2)t
    l

    Rate of heat flow
    H =
    Q
    		 =
    KA(θ1 - θ2)
    		i.e., H ∝
    A
    tll

    Dimensions of area A = [L²], dimensions of distance l = [L]
    ∴ H ∝ L ⇒
    H2
    		 =
    L2
    		 = 2 ⇒ H2 = 2H1
    H1L1

    Correct Option: B

    Q =
    KA(θ1 - θ2)t
    l

    Rate of heat flow
    H =
    Q
    		 =
    KA(θ1 - θ2)
    		i.e., H ∝
    A
    tll

    Dimensions of area A = [L²], dimensions of distance l = [L]
    ∴ H ∝ L ⇒
    H2
    		 =
    L2
    		 = 2 ⇒ H2 = 2H1
    H1L1

  1. The presence of gravitational field is required for the heat transfer by








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    In convection, the temperature gradient exists in the vertical direction and not in the horizontal direction. So, up and down movement of particles takes place which depends on the weight and gravity.

    Correct Option: C

    In convection, the temperature gradient exists in the vertical direction and not in the horizontal direction. So, up and down movement of particles takes place which depends on the weight and gravity.

  1. The radiant energy from the sun, incident normally at the surface of earth is 20 k cal/m² min. What would have been the radiant energy, incident normally on the earth, if the sun had a temperature, twice of the present one?








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    According to Stefan’s law E ∝ T4

    E1
    		 =
    T14
    		 Or,
    20
    		 =
    T4
    E2T24E224T4

    E2 = 320 kcal/m². min.

    Correct Option: C

    According to Stefan’s law E ∝ T4

    E1
    		 =
    T14
    		 Or,
    20
    		 =
    T4
    E2T24E224T4

    E2 = 320 kcal/m². min.