The top of a lake gets frozen at a place where the surrounding air is at a temperature of $-20\,^oC$. Then
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  • 1
    Assertion : The equivalent thermal conductivity of two plates of same thickness in contact is less than the smaller value of thermal conductivity.
    Reason : For two plates of equal thickness in contact the equivalent thermal conductivity is given by : $\frac{1}{K} = \frac{1}{{{K_1}}} + \frac{1}{{{K_2}}}$
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  • 2
    Three objects colored black, gray and white can withstand hostile conditions upto $2800\,^oC$. These objects are thrown into a furnace where each of them attains a temperature of $2000\,^oC$. Which object will glow brightest?
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  • 3
    Which of the following is more closed to a black body?
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  • 4
    Heat is flowing through a conductor of length l from $x = 0$ to $x = l$ . If its thermal resistance per unit length is uniform, which of the following graphs is correct
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  • 5
    Which of the following cylindrical rods will conduct most heat, when their ends are maintained at the same steady temperature
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  • 6
    Gravitational force is required for
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  • 7
    In Newton's experiment of cooling, the water equivalent of two similar calorimeters is $10 $ gm each. They are filled with $350 gm$ of water and $300 gm$ of a liquid (equal volumes) separately. The time taken by water and liquid to cool from ${70^o}C$ to ${60^o}C$ is $3$ min and $95$ sec respectively. The specific heat of the liquid will be ...... $Cal/gm\,^oC$
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  • 8
    $A$ metal rod of length $2$$m$ has cross sectional areas $2A$ and $A$ as shown in figure. The ends are maintained at temperatures $100°C$ and $70°C$ . The temperature at middle point $C$ is...... $^oC$
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  • 9
    A composite rod made of three rods of equal length and cross-section as shown in the fig. The thermal conductivities of the materials of the rods are $K/2, 5K$ and $K$ respectively. The end $A$ and end $B$ are at constant temperatures. All heat entering the face Agoes out of the end $B$ there being no loss of heat from the sides of the bar. The effective thermal conductivity of the bar is
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  • 10
    If the radius of a star is $R$ and it acts as a black body, what would be the temperature of the star, in which the rate of energy production is Q? ( $\sigma$ stands for Stefan's constant.)
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