To convert heat energy into electrical energy efficiently, a material needs to have specific properties:
- Low thermal conductivity: This ensures that heat is retained in the material and does not dissipate too quickly, which is essential for converting heat energy into electrical energy.
- High electrical conductivity: This allows for efficient conduction of the electricity generated from the heat.
When the temperature difference across the material is used for energy conversion (such as in thermoelectric materials), the Seebeck effect occurs. In this process, a temperature difference across the material results in the generation of an electric voltage. To maximize this effect, the material should have low thermal conductivity (to trap the heat) and high electrical conductivity (to conduct the generated electricity).
Therefore, the correct answer is (3) low thermal conductivity and high electrical conductivity.
Two vessels A and B are connected via stopcock. Vessel A is filled with a gas at a certain pressure. The entire assembly is immersed in water and allowed to come to thermal equilibrium with water. After opening the stopcock the gas from vessel A expands into vessel B and no change in temperature is observed in the thermometer. Which of the following statement is true?
Match List - I with List - II.
Choose the correct answer from the options given below :
Match List - I with List - II:
List - I:
(A) Electric field inside (distance \( r > 0 \) from center) of a uniformly charged spherical shell with surface charge density \( \sigma \), and radius \( R \).
(B) Electric field at distance \( r > 0 \) from a uniformly charged infinite plane sheet with surface charge density \( \sigma \).
(C) Electric field outside (distance \( r > 0 \) from center) of a uniformly charged spherical shell with surface charge density \( \sigma \), and radius \( R \).
(D) Electric field between two oppositely charged infinite plane parallel sheets with uniform surface charge density \( \sigma \).
List - II:
(I) \( \frac{\sigma}{\epsilon_0} \)
(II) \( \frac{\sigma}{2\epsilon_0} \)
(III) 0
(IV) \( \frac{\sigma}{\epsilon_0 r^2} \) Choose the correct answer from the options given below:
Consider the following statements:
A. Surface tension arises due to extra energy of the molecules at the interior as compared to the molecules at the surface of a liquid.
B. As the temperature of liquid rises, the coefficient of viscosity increases.
C. As the temperature of gas increases, the coefficient of viscosity increases.
D. The onset of turbulence is determined by Reynolds number.
E. In a steady flow, two streamlines never intersect.
Choose the correct answer from the options given below: