# Two rods of identical dimensions are joined end-to-end, and the ends of the composite rod are kept at $$0^\circ\mathrm{ C}$$ and $$100^\circ\mathrm{ C}$$ (as shown in the diagram). The temperature of the joint is found to be $$40^\circ\mathrm{ C}.$$ Assuming no loss of heat through the sides of the rods, the ratio of the conductivities of the rods $$K_1/K_2$$ is:                       1. $$\frac32$$ 2. $$\frac23$$ 3. $$\frac11$$ 4. $$\frac{\sqrt3}{\sqrt2}$$

Subtopic:  Conduction |
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The temperature at which the Celsius and Fahrenheit thermometers agree (to give the same numerical value) is:
1. $$-40^\circ$$
2. $$40^\circ$$
3. $$0^\circ$$
4. $$50^\circ$$

Subtopic:  Temperature and Heat |
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The ice-point reading on a thermometer scale is found to be $$20^\circ,$$ while the steam point is found to be $$70^\circ.$$ When this thermometer reads $$100^\circ ,$$ the actual temperature is:
1. $$80^\circ~\mathrm{C}$$
2. $$130^\circ~\mathrm{C}$$
3. $$160^\circ~\mathrm{C}$$
4. $$200^\circ~\mathrm{C}$$

Subtopic:  Temperature and Heat |
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A rod $$\mathrm{A}$$ has a coefficient of thermal expansion $$(\alpha_A)$$ which is twice of that of rod $$\mathrm{B}$$ $$(\alpha_B)$$. The two rods have length $$l_A,~l_B$$ where $$l_A=2l_B$$. If the two rods were joined end-to-end, the average coefficient of thermal expansion is:
1. $$\alpha_A$$
2. $$\frac{2\alpha_A}{6}$$
3. $$\frac{4\alpha_A}{6}$$
4. $$\frac{5\alpha_A}{6}$$

Subtopic:  Thermal Expansion |
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If the ends of the meter stick are maintained at $$\theta_1$$$$^\circ \text{C}$$ and $$\theta_2$$$$^\circ \text{C},$$ the temperatures measured at the $$25$$ cm and $$80$$ cm marks are observed to be $$35^\circ \text{C}$$ and $$68^\circ \text{C}$$ respectively. Then the temperatures of the left end ($$\theta_1$$$$^\circ \text{C}$$) and the right end ($$\theta_2$$$$^\circ \text{C}$$) are:
 1 $$\theta_{1}=0, ~\theta_{2}=90$$ 2 $$\theta_{1}=10,~\theta_{2}=85$$ 3 $$\theta_{1}=20, ~\theta_{2}=80$$ 4 $$\theta_{1}=30, ~\theta_{2}=100$$
Subtopic:  Conduction |
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When the temperature difference between a body and its surroundings is $$20$$°C, it loses heat to the surroundings at a rate of $$40$$ W. If the temperature difference increases to $$25$$°C, the rate of loss of heat is:
1. $$45$$
2. $$50$$ W
3. $$60$$
4. $$80$$ W
Subtopic:  Newton's Law of Cooling |
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Two liquids flow through a heat exchanger and exchange heat energy.
The first liquid has a mass flow rate $$\Big(\dfrac{dm}{dt}\Big)=r_1,$$ and its temperature rises by $$\Delta\theta_1.$$ For the second liquid, the flow rate $$\Big(\dfrac{dm}{dt}\Big)=r_2,$$ and the temperature fall is $$\Delta\theta_2.$$ The ratio of their specific heat capacities is:
1.  $$\dfrac{\Delta\theta_1}{\Delta\theta_2}$$
2.  $$\dfrac{r_1}{r_2}$$
3.  $$\dfrac{r_2\Delta\theta_2}{r_1\Delta\theta_1}$$
4.  $$\dfrac{r_2\Delta\theta_1}{r_1\Delta\theta_2}$$
Subtopic:  Calorimetry |
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A body cools from $$52^\circ \text{C}$$ to $$48^\circ \text{C}$$ in $$6$$ minutes. How much time will the same body take to cool from $$53^\circ \text{C}$$ to $$47^\circ \text{C}?$$ Assume cooling is linear with time.
1. $$12$$ minutes
2. $$9$$ minutes
3. $$8$$ minutes
4. $$7$$ minutes
Subtopic:  Newton's Law of Cooling |
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A solid at temperature T1, is kept in an evacuated chamber at temperature T2 > T1 . The rate of increase of temperature of the body is proportional to

1. T2 – T1

2.   $$T^2_2 -T^2_1$$n

3.   $$T^3_2 -T^3_1$$

4.   $$T^4_2 -T^4_1$$

Subtopic:  Stefan-Boltzmann Law |
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In a room containing air, heat can go from one place to another:
1. by conduction only
2. by convection only
3. by radiation only
4. by all three modes

Subtopic:  Convection |
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