Thermal | MCQs

Explanation

Efficiency is the ratio of output to input, often expressed as a percentage.

It represents how much of the input energy is actually converted into useful output energy, with the rest being lost as waste or heat.

Key Points:

• Energy is the ability to do work.
• Work is the transfer of energy through a force applied over a distance.
• Power is the rate at which work is done or energy is transferred.

Explanation

When a gas changes into a liquid, the molecules:

• Move closer together (their distance decreases)
• Lose kinetic energy (they slow down)

Explanation

When a gas is heated in a container of fixed volume, the molecules of the gas:

• Move faster (their kinetic energy increases, causing them to move more rapidly)
• Collide more frequently with the container walls (resulting in increased pressure)
• Do not expand (the container volume is fixed)
• Do not move further apart (the density of the gas remains the same, as the volume

Explanation

When a gas is heated in a sealed cylinder:

• The temperature of the gas increases (by definition of heating).
• The average kinetic energy of the particles increases (as the temperature rises, the molecules move faster).
• The pressure inside the container increases (as the molecules move faster and collide more frequently with the container walls).

Explanation

A microwave oven heats food by using electromagnetic radiation at a specific frequency

That resonates with the water molecules in the food, causing them to vibrate and generate heat.

This process of energy transfer due to matching frequencies is called resonance. 

Explanation

 Those substances through which electric current cannot pass are called insulators.

Insulators have very high electrical resistance

. For example, wood, rubber, glass, paper, plastic and wax are insulators of electricity.

Insulators cannot conduct electricity due to absence of free electrons in them.

Explanation

A heat detector is used for finding fires by detecting significant increases in temperature

Types:

Some heat detectors respond to a rapid temperature increase ("rate-of-rise"),

While others activate when a specific temperature is reached ("fixed temperature"). 

Explanation

Maximum molar volume is at 127°C and 1 atm = 32.84 L

Explanation

 A rotary kiln used in waste treatment (like incineration or cement production) typically has four zones:

   - Drying zone

   - Preheating zone

   - Combustion zone

   - Cooling zone

Explanation

• Air expands the most for a given rise in temperature, due to its low density and high thermal expansion coefficient.
• This is why hot air rises and cool air sinks, driving convection currents in the atmosphere.