Thermal Resistance

Q. Four rods of silver, copper, brass and wood are of same shape. They are heated together after wrapping a paper on it, the paper will burn first on

1. Silver
2. Copper
3. Brass
4. Wood

Q.
Find the $R_{equivalent}$.

1. $\frac{R_1{R}_2}{R_1+R_2}$
2. $R_2$
3. $R_1+R_2$
4. $R_1$

Q.
Find the heat current, i.

1. $\left(\frac{K_1^2{K}_2^{2}A}{l_1{K}_2^2+l_2{K}_1^2}\right)\Delta T$
2. $\left(\frac{K_1{K}_{2}A}{l_1{K}_2+l_2{K}_1}\right)\Delta T$
3. $\left(\frac{K_1{K}_{2}A}{l_2{K}_2+l_1{K}_1}\right)\Delta T$
4. $\left(\frac{K_{1}A}{l_1+l_2}\right)\Delta T$

Q. Heat conduction is the property of __________.

1. Non-metals
2. Metals
3. Metalloids
4. All of these

Q.

Two conducting rods A and B of same length and cross-sectional area are connected (i) In series (ii) In parallel as shown. In both combination a temperature difference of ${100}^{\circ }$ C​ is maintained. If thermal conductivity of A is 3K and that of B is K then the ratio of heat current flowing in parallel combination to that flowing in series combination is

1. 
2. 
3. 
   
4. 

Q.
Find the $R_{equivalent}$.

1. $R_1$
2. $R_2$
3. $R_1+R_2$
4. $\frac{R_1{R}_2}{R_1+R_2}$

Q. In the following figure, two insulating sheets with thermal resistances R and 3R as shown in figure. The temperature $\theta$ is

1. C
2. C
3. C
4. C

Q. A steel drill is making $180$ Revolutions per minute, under a constant torque of $5N-m$. If it drills a hole in $7s$. in a steel block of mass $600gm$, rise in temperature of the block is $(s=0.1cal/gm/$${}^{\circ }C$)

1. ${2.6}^{\circ }C$
2. ${1.3}^{\circ }C$
3. ${5.2}^{\circ }C$
4. $3^{\circ }C$

Q.

Three rods of material x and three of material y are connected as shown in figure. All the rods are identical in length and cross-sectional area. If the end A is maintained at 60${}^{\circ }$C and the junction E at 10 ${}^{\circ }$ C, calculate the temperature of the junction B. The thermal conductivity of x is 800 W/M- ${}^{\circ }$ C and

that of y is 400 W/M- ${}^{\circ }$ C

1. 60⁰C

2. 50⁰C

3. 20⁰C

4. 40⁰C

Q. A solid cylinder of radius R made of a material of thermal conductivity $K_1$ is surrounded by a cylindrical shell of inner radius R and outer radius $2R$ made of a material of thermal conductivity $K_2$. The two ends of the combined system are maintained at two different temperatures. Then there is no loss of heat across the cylindrical surface and the system is in steady state. The effective thermal conductivity of the system is:

1. $\frac{4K_1+3K_2}{4}$
2. $\frac{3K_1+4K_2}{4}$
3. $\frac{3K_1+K_2}{4}$
4. $\frac{K_1+3K_2}{4}$

Q. Two uniform rods of equal length but different masses are rigidly joined to form an $L$ shaped body, which is then smoothly pivoted about $O$ as shown. If the body is in equilibrium in the shown configuration, ratio $M:m$ will be :

1. $2$
2. $3$
3. $\sqrt{2}$
4. $\sqrt{3}$

Q. Describe a method to determine the specific heat capacity of a solid, like a piece of copper.

1. 0