Tag: conduction in metals and non-metals

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Multiple choice conduction in metals and non-metals thermal energy transfers physics

Two identical bodies are made of a material for which the heat capacity increases with temperature. One of these is at ${ 100 }^{ 0 }$, while the other one is at ${ 0 }^{ 0 }C$. If the two bodies are brought into contact, then assuming no heat loss, the final common temperature is

  1. ${ 50 }^{ 0 }C$
  2. more than ${ 50 }^{ 0 }C$
  3. less than ${ 50 }^{ 0 }C$ but greater than ${ 0 }^{ 0 }C$
  4. ${ 0 }^{ 0 }C$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Since heat capacity increases with temperature, the body at 100 degrees Celsius has a larger heat capacity than the identical body at 0 degrees Celsius. When they reach thermal equilibrium, more heat is required to raise the temperature of the colder body per degree than the heat released by the hotter body, shifting the final common temperature higher than the simple arithmetic mean of 50 degrees Celsius.

Multiple choice conduction in metals and non-metals thermal energy transfers physics

When a thermometer is taken from the melting ice to a warm liquid, the mercury level rises to two-fifths of the distance between the lower and the upper fixed points. Find the temperature of the liquid $(i)i{n^o}C,and(ii)\;in\;K.$ 

  1. ${40^0}C.313K$
  2. ${30^0}C.227K$
  3. ${20^0}C.273K$
  4. ${0^0}C.0K$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The Celsius scale has 100 divisions between 0 and 100. Two-fifths of 100 is 40 degrees Celsius. Converting to Kelvin, 40 + 273.15 = 313.15 K, which rounds to 313 K.

Multiple choice conduction in metals and non-metals thermal energy transfers physics

In winter , temprature of bottom of take is 4$$C . Ratio of thermal conductance of ice and water is 2:3 and depth of the take 20 m. Find the maximum thickness os ice formed .  

  1. $\frac { 200 }{ 11 } M$
  2. $\frac { 100 }{ 8 } M$
  3. $\frac { 220 }{ 12 } M$

  4. 10 M
Reveal answer Fill a bubble to check yourself
C Correct answer
Multiple choice conduction in metals and non-metals thermal energy transfers physics

A semicircular rod is joined at its end to a straight rod of the same material and the same cross-sectional area. The straight rod forms a diameter of the other rod. The junctions are maintained at different temperatures. Find the ratio of the heat transferred through a cross-section of the semicircular rod of the heat transferred through a cross-section the straight rod in the given time.

  1. $\dfrac 2\pi$
  2. $\dfrac 1\pi$
  3. $\dfrac 1{2\pi}$
  4. $\dfrac \pi2$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Heat flow rate is proportional to cross-sectional area and inversely proportional to length. For a semicircular rod of radius R, the length is pi*R and area is A. For the straight diameter rod, length is 2R and area is A. The ratio of heat flow (H_semi / H_straight) = (K*A*dT / (pi*R)) / (K*A*dT / (2*R)) = 2/pi.

Multiple choice conduction in metals and non-metals thermal energy transfers physics

Bimetallic thermostat consists two metals of different thermal co-efficient thermostat always bends towards material having
(i)large thermal expansion on heating 
(ii)large thermal expansion on cooling
(iii)small thermal expansion on heating
(iv)small thermal expansion on cooling

  1. I only

  2. II only

  3. III and II only

  4. I and IV only
Reveal answer Fill a bubble to check yourself
C Correct answer
Multiple choice conduction in metals and non-metals thermal energy transfers physics

The ratio of radii of two spheres of same material is  $1:4 .$  Then the ratio of their heat  capacity will be

  1. $\dfrac { 1 } { 64 }$
  2. $\dfrac { 1 } { 32 }$
  3. $\dfrac { 1 } { 2 }$
  4. $\dfrac { 1 } { 4 }$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Heat capacity is the product of mass and specific heat capacity (C = m * s). Since both spheres are made of the same material, their specific heats are equal, making heat capacity proportional to mass, and thus proportional to volume (or r cubed). The ratio of radii is 1:4, so the ratio of their heat capacities is (1/4)^3 = 1/64.

Multiple choice conduction in metals and non-metals thermal energy transfers physics

A heat engine takes steam at $200^oC$ and after doing work exhausts it directly into air at $100^oC$. Calculate the percentage of heat which is wasted.

  1. $58.86$
  2. $68.86$
  3. $48.86$
  4. $78.86$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The maximum theoretical efficiency of a heat engine is given by the Carnot efficiency formula: Efficiency = 1 - (T_sink / T_source). Converting temperatures to Kelvin: T_source = 200 + 273 = 473 K and T_sink = 100 + 273 = 373 K. Efficiency = 1 - (373 / 473) = 1 - 0.7886 = 0.2114 or 21.14 percent, meaning the percentage of heat wasted is 100 - 21.14 = 78.86 percent.

Multiple choice conduction in metals and non-metals thermal energy transfers physics

Which of the following material is most suitable for cooking utensil ?

  1. Low conductivity and low specific heat

  2. High conductivity and low specific heat

  3. Low conductivity and High specific heat

  4. High conductivity and High specific heat
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

A cooking utensil requires high thermal conductivity to transfer heat quickly and efficiently from the source to the food. It also requires low specific heat capacity so that the utensil itself does not absorb excessive heat and changes temperature rapidly.

Multiple choice conduction in metals and non-metals thermal energy transfers physics

Two angular blocks A and B different metal have same length and same area of cross-section . they are kept in such a way that their cross-sectional area touch each other. the temperature at one end of A is $ 100^0 $ C and that of B at the other end is $0^0 C $ C . if the ratio of their conductivity is 1:3 then under steady state, the temperature of the junction in contact will be:-

  1. $ 25^0 C $
  2. $ 50^0 C $
  3. $ 75^0 C $
  4. $ 100^0 C $
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

In steady state, the rate of heat flow through block A equals that through block B. Using the conduction formula (K * A * deltaT / L), since lengths and areas are equal, K1 * (100 - T) = K2 * (T - 0). Given K1:K2 = 1:3, 1 * (100 - T) = 3 * (T - 0), which gives 100 - T = 3T, resulting in 4T = 100 and T = 25 degrees Celsius.

Multiple choice conduction in metals and non-metals thermal energy transfers physics

On heating one end of a rod, the temperature of the whole rod will be uniform when the :

  1. $k $ $ = 1$
  2. $k $ $ = 0$
  3. $k $ $ = 100$
  4. $k $ $ = \infty $
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

If temperature of whole rod is same, it means that heat is being conducted from one end to other infinitely fast. This is possible only when thermal conductivity is infinite.