1.
A thermos flask consists of a double‑walled glass container with a vacuum between the walls. The vacuum prevents heat energy from being transferred by
Correct Answer
D. Conduction, convection and radiation only
Explanation
The thermos flask is designed to minimize heat transfer by conduction, convection, and radiation. The double-walled glass container creates a vacuum between the walls, which prevents heat conduction by eliminating any material contact between the inner and outer walls. The vacuum also inhibits heat convection by eliminating the presence of air or any other medium that could transfer heat through convection currents. Finally, the glass walls of the flask reflect and absorb thermal radiation, preventing it from entering or escaping the flask. Therefore, the correct answer is conduction, convection, and radiation only.
2.
A silver spoon and a plastic spoon are placed on a table in a room. The silver spoon is colder to the touch because silver is a better
Correct Answer
B. Conductor of heat energy than plastic
Explanation
Trick question. Both spoons are at the same temp, note. Because they are in the same environment.
3.
An unlit match is held near to an extremely hot Bunsen flame as shown in the figure. The match does not get hot enough to light because
Correct Answer
C. Air is a bad conductor of heat energy
Explanation
The match does not get hot enough to light because air is a bad conductor of heat energy. This means that heat is not efficiently transferred from the extremely hot Bunsen flame to the match. Since the match does not receive enough heat, it does not reach the temperature required for ignition.
4.
Water in a beaker is heated at X. Which diagram best shows the convection currents?
Correct Answer
D. D
Explanation
Diagram D shows convection currents in the beaker when it is heated. The heat causes the water molecules near the bottom of the beaker to gain energy and become less dense, causing them to rise. As they rise, they carry the heat with them. At the top, the water molecules release the heat and cool down, becoming denser and sinking back down. This creates a continuous circular motion of warm water rising and cool water sinking, which is characteristic of convection currents. Diagram D accurately represents this process.
5.
Which of the following is the poorest conductor of heat energy?
Correct Answer
C. A vacuum
Explanation
A vacuum is the poorest conductor of heat energy because it is devoid of any particles or molecules that can transfer heat through conduction. Unlike air, water, or wool, which all contain particles that can transfer heat, a vacuum is a complete absence of matter, making it an excellent insulator. Heat energy cannot be conducted through a vacuum, as there are no particles to transfer the energy from one place to another.
6.
The figure represents a section through a particular type of building board.Which one of the followings shows why such boards provide good insulation of thermal energy?
( Aluminium foil ) ( expanded polystyrene )
Correct Answer
A. (a good reflector), (a poor conductor)
Explanation
The figure represents a section through a particular type of building board. The board provides good insulation of thermal energy because it is a good reflector and a poor conductor. Being a good reflector means that it reflects thermal energy back instead of allowing it to pass through the board. This helps in preventing heat transfer. Additionally, being a poor conductor means that the board does not easily transfer heat through its material, further enhancing its insulation properties.
7.
A metal ball heated to a temperature of 200°C is placed in a room of temperature of 30°C. At which temperature will it stop radiating heat energy?
Correct Answer
E. None of the above
Explanation
When a metal ball is heated to a higher temperature than its surroundings, it will continue to radiate heat energy until it reaches thermal equilibrium with the room. Thermal equilibrium is achieved when the object and its surroundings are at the same temperature. Therefore, the metal ball will stop radiating heat energy when it reaches the room temperature of 30°C, not at any of the temperatures listed in the answer choices.
8.
The hot water for a house can be produced by absorbing solar energy, using copper panels through which the water circulates. What is the best finish for the top surface of the copper panels?
Correct Answer
B. Dull black paint
Explanation
The best finish for the top surface of the copper panels would be dull black paint. This is because black surfaces absorb more heat than any other color, and a dull finish helps to increase the absorption of solar energy. Therefore, by using dull black paint on the top surface of the copper panels, the panels will be able to absorb more solar energy and efficiently produce hot water for the house.