Thermal Properties of Matter

Thermal Properties of Matter

Moderate Questions
Difficult Questions

Thermal Physics

Thermal Properties of Matter
Thermodynamics
Kinetic Theory
  1. The total radiant energy per unit area, normal to the direction of incidence, received at a distance R from the centre of a star of radius r, whose outer surface radiates as a black body at a temperature T K is given by:








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    E =
    S
    		σ T4 =
    4πr²
    		σ T4
    S04πR²

    = σ
    r²
    		T4
    R²

    Correct Option: A

    E =
    S
    		σ T4 =
    4πr²
    		σ T4
    S04πR²

    = σ
    r²
    		T4
    R²

  1. An electric kettle takes 4A current at 220 V. How much time will it take to boil 1 kg of water from temperature 20° C? The temperature of boiling water is 100° C.








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    Heat required to raise the temperature of 1kg water from 20°C to 100°C is given by Q = ms∆θ = (1× 4200 × 80) J
    Power of kettle (P) = VI = (220 × 4)W

    ∴ Time taken =
    Q
    		 =
    1 × 4200 × 80
    		 = 381.81 sec = 6.36 min
    P220 × 4

    Correct Option: A

    Heat required to raise the temperature of 1kg water from 20°C to 100°C is given by Q = ms∆θ = (1× 4200 × 80) J
    Power of kettle (P) = VI = (220 × 4)W

    ∴ Time taken =
    Q
    		 =
    1 × 4200 × 80
    		 = 381.81 sec = 6.36 min
    P220 × 4

  1. A black body is at 727° C. It emits energy at a rate which is proportional to








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    According to Stefan's law,
    E ∝ T4
    ∝ (t + 273)4 K [727°C = (727 + 273)K]
    ∝ (727 + 273)4 K
    ∝ (1000)4 K

    Correct Option: A

    According to Stefan's law,
    E ∝ T4
    ∝ (t + 273)4 K [727°C = (727 + 273)K]
    ∝ (727 + 273)4 K
    ∝ (1000)4 K

  1. Assuming the sun to have a spherical outer surface of radius r, radiating like a black body at temperature t°C, the power received by a unit surface, (normal to the incident rays) at a distance R from the centre of the sun is








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    Power radiated by the sun at t°C
    = σ(t + 273)4 4πr²
    Power received by a unit surface

    =
    σ(t + 273)4 4πr²
    		 =
    r²σ(t + 273)4
    4πR²R²

    Correct Option: C

    Power radiated by the sun at t°C
    = σ(t + 273)4 4πr²
    Power received by a unit surface

    =
    σ(t + 273)4 4πr²
    		 =
    r²σ(t + 273)4
    4πR²R²

  1. A black body at 1227°C emits radiations with maximum intensity at a wavelength of 5000Å. If the temperature of the body is increased by 1000°C, the maximum intensity will be observed at








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    Applying Wein's displacement law,
    λmT = constant
    5000 Å × (1227 + 273) = (2227 + 273) × λm

    λm =
    5000 × 1500
    		 = 3000 A
    1000

    Correct Option: C

    Applying Wein's displacement law,
    λmT = constant
    5000 Å × (1227 + 273) = (2227 + 273) × λm

    λm =
    5000 × 1500
    		 = 3000 A
    1000