True or false
(i) Steel is better conductor of heat than bricks.
(ii) Radiations are ultrasonic waves.
(iii) Black body is having emissivity 2.
(iv) Natural convection do not need any external source for fluid flow.
(v) Fins cause increase in rate of heat transfer
1] True
2] False
3] False
4] True
5] True
explain thermal conductivity & give its variation in case of solids liquids & gases
(i) To determine whether steel is a better conductor of heat than bricks, we need to compare their thermal conductivities. The thermal conductivity of a material refers to its ability to conduct heat. Steel has a higher thermal conductivity than bricks, so the statement is true. One way to find this information is by referring to material property databases or engineering handbooks.
(ii) Radiations are not ultrasonic waves. Ultrasonic waves are mechanical vibrations of particles that have a frequency greater than the upper limit of human hearing. On the other hand, radiations refer to the emission or transmission of energy in the form of electromagnetic waves. These waves have a wide range of frequencies, including radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays. To find more information about the different types of waves, you can refer to physics textbooks or online resources.
(iii) The emissivity of a black body is not 2. The emissivity of a surface indicates its ability to emit thermal radiation compared to an ideal black body. A black body has an emissivity of 1, meaning it emits radiation efficiently. The emissivity of other surfaces can be less than or equal to 1, but not greater than 1. You can find tables or resources that provide emissivity values for different materials to confirm this.
(iv) Natural convection does not require any external source for fluid flow. Natural convection occurs when a fluid (gas or liquid) experiences buoyancy-driven flow due to temperature differences within the fluid itself. As the fluid near a heat source becomes warmer, it becomes less dense and rises, while the cooler fluid surrounding it moves in to take its place. This creates a continuous flow of fluid. No external mechanical device (such as a pump or fan) is needed for natural convection to occur. Understanding the principles of convection and the differences between natural and forced convection will help you confirm this statement.
(v) Fins do cause an increase in the rate of heat transfer. Fins are extended surfaces attached to a primary surface to increase the surface area available for heat transfer. They increase the rate of heat transfer through conduction by providing additional pathways for heat to flow. The increased surface area enables more contact with the surrounding medium (air or liquid), facilitating efficient heat transfer. To verify this statement, you can study principles of heat transfer or refer to engineering literature and heat exchanger design references.