Heat transfer

Why are there small gaps between rails?

• The small gaps provide space for easy expansion of rails during hotter weather.

• The small gaps allow air to keep the noise low for hotter weather.

• The small gaps are not important

• There are small gaps due to aesthetics

Which of the images best describe thermal expansion of solid?

• 
• 
• 
• 

From a metallic wall at 100°C, a metallic rod protrudes to the ambient air. The temperatures at the tip will be minimum when the rod is made of:

• Aluminium

• Steel

• Copper

• Silver

Emissivity of a white polished body in comparison to a black body is

• Higher

• Lower

• Same

• Depends upon the shape of body

For calculation of heat transfer by natural convection from a horizontal cylinder, what is the characteristic length in Grashof Number?

• Diameter of the cylinder

• Length of the cylinder

• Circumference of the base of the cylinder

• Half the circumference of the base of the cylinder

In forced convection heat transfer transition from laminar to turbulent flow is governed by the critical value of the  

• Reynolds number

• Grashoff's number

• Reynolds number, Grashoff number

• Prandtl number, Grashoff number

The process of heat transfer from one particle of the fluid to another by the actual movement of the fluid particles due to difference of density caused by temperature of the particle is known as

• Conduction

• Free convection

• Forced convection

• Radiation

A student must choose three items to demonstrate conduction, convection, and radiation from solar energy. The student quickly chooses water and a metal bowl. Which of the following items should the student choose to complete the experiment?

• Rubber ball

• food coloring

• heat lamp

• ice cube

What is the equation to measure change in Thermal Energy?

• 
  Q=mc∆t

• 
  Q=mc

• Q= ∆mct

• m=QC

When a stethoscope touches your skin, what happens?

• heat travels from the stethoscope to your skin

• no energy is transferred

• the stethoscope warms up due to humidity

• heat travels from your warm body to the stethoscope