Heat Flashcards
What is heat.
Heat is a form of energy which causes a sensation of hotness or coldness. When there is a difference in temperature between two bodies, heat transfers from the body with the higher temperature to the body with the lower temperature.
What is equilibrium temperature.
When there are two bodies of different temperatures, the body with the higher temperature will keep transferring heat energy to the body with the lower temperature till they are both of the same temperature.
Units of heat
The SI until of heat is joule and the CGS unit of heat is calorie. One calorie is the amount of heat needed to rise the temperature of 1 gm of water by 1 centigrade. 1 calorie = 4.2 joule and 1 joule = 1/4.2 calorie.
Heat brings about change in temperature
When we supply heat to an object, it’s temperature increases . In the same way, when abody gives out heat its temperature decreases
Heat brings about change in dimensions
When we increase the temperature of abody, is dimensions such as length, breadth and height changes when the body is heated, the molecules, more faster from and away each other. Heat provides more energy to the molecules, thus resulting in change of dimensions
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Why are there small gaps between the railway tracks.
When heat is provided to a solid, it goes under superficial cubicle and linear expansion. So in the summer, when the sun heats up the railway tracks, they might expand and overlap each other, which may cause accidents to avoid that we leave gaps in between railway tracks, so that they have space to expand these gaps are insignificant and do not cause any harm.
Expansion in liquids
Liquids have definite volume, but not definite shape, so they go through cubicle expansion. Their molecules are less tightly packed than that of solids so they vibrate, more vigourously and expand more. When we take a temperature of an object which has a high temperature the mercury within the thermometer, expand .
Expansion of gases
Gases have no definite volume but have a definite shape in an enclosed vessel so they only show cubicle expansion, their molecules vibrate, much more vigourously than that of solids and liquids for example, the air inside a hot air balloon expands due to heating the air rises in the balloon and pushes the colder air out.   thus  the balloon gets filled  with hot and expanded air  as the air inside the balloon is less dense than the air outside the balloon. The hot air balloon rises.
Heat brings about change in state
 When we heat a solid, it changes into a liquid. Similarly, when we heat a liquid changes into vapour.
What is conduction? 
Conduction is a method of heat transfer. It happens when two bodies are in contact with each other and the heat flows from the body with the higher temperature to the body with the lower temperature. This method of transfer of heat requires a medium and cannot happen in a vacuum. For example, if we take a metal rod  and stick metal paper clips by wax and rest it onto wooden sticks and apply heat to one of the sides. We will notice that the paperclip start falling in an order from closest to where the heat is applied to the farthest.  when we apply heat to these particles, they start vibrating vigourously and collide with the neighbouring particles the pass on their heat energy to the neighbouring particles. This continues until the whole body is heated. This is conduction 
What are conductors?
Conductors are the materials that allow heat energy to pass through them easily.  Most metals are very good conductors of heat. Silver is the best conductor of heat.
 What are insulators?
 Insulators are materials that do not let heat energy pass through them easily
Why do we prefer to wear woollen clothes in winter?
 We prefer to wear woollen clothes in winter because wool is an insulator. So it will trap the heat from our body and keep us warm. 
What is convection?
We know that water and air are not good conductors of heat So transfer of heat by conduction is not possible. Convection is the transfer of heat by actual movement of the molecules. 
What is land breeze and what is the sea breeze?
Sea breeze takes place during the day. During the day, the land heats up faster than the sea the air above the land becomes warm and since it is less dense, it rises up. The cold air above the sea immediately rushes to take the place of the warm air. This cycle continues and this is known as sea breeze
