Heat

• Heat is a form of energy that flows from a hotter region to a colder region, with various sources including the Sun, electric appliances, and burning of fuel.
• Temperature is a measure of the degree of hotness or coldness of an object, which increases in a hot environment and decreases in a cold environment.
• Temperature is measured using a thermometer.
• Heat is measured in joules (J) and degrees Celsius (°C) or kelvin (K).
• The amount of heat depends on the types of material and the quantity of material.
• Temperature depends on the degree of movement of the particles in a matter.
• Conduction is the process of heat transfer from hotter regions to colder regions through a solid medium.
• The particles that receive heat energy will vibrate and collide with one another more frequently and transfer the heat to the whole medium.
• Convection is the transfer of heat by the movement of fluid (liquid and gas) from hotter regions to colder regions.
• Hot particles expand and become less dense, rising.
• Cold particles are more dense and move downwards.
• The circulating stream that rises and falls continuously is known as convection current.
• Radiation is the transfer of heat without any medium.
• Heat can not propagate through an empty space or vacuum.
• The types of surface, temperature and total surface area of an object will influence the rate of heat flow.
• Heat Conductors are materials that allow heat to flow, such as the base of an iron, made of metal, which enables it to conduct heat.
• Heat Conductors include materials that allow heat to flow quickly to the food, like the bottom of a pan, made of metal.
• Mercury in thermometers is a good heat conductor that can detect change in temperature very quickly.
• Heat Insulators are materials that prevent heat from flowing through, such as oven gloves, which prevent your hands from getting scalded while taking food trays out from the oven.
• Cooking utensils made of wood are capable of preventing heat from flowing to the hand while cooking.
• The wall of an ice box, made of fibreglass or polystyrene, maintains the coolness of substances inside the box.
• Two objects which are in thermal contact can exchange heat energy between them.
• When there is no net transfer of heat energy between the objects, the objects are said to be in thermal equilibrium.
• Two objects that are in thermal equilibrium have the same temperature.
• In a solid, particles vibrate at a fixed position.
• When heated, particles vibrate faster and move further apart from one another, causing the volume of the solid to increase.
• When cooled, particles vibrate slower and move closer to one another, decreasing the volume of the solid.
• In a liquid and gas, particles move freely.
• When heated, particles move faster and randomly, increasing the distance between particles and increasing the volume of the liquid and gas.
• When cooled, particles move slower and closer to one another, decreasing the volume of the liquid and gas.
• Mercury in a thermometer is a heat conductor and can expand and contract.
• Railway tracks have small gaps between their rails to enable them to expand in hot weather.
• Steel bridges are built with rollers and a gap on one end to allow the bridges to expand in hot weather.
• Bimetallic strip, used in devices that depend on temperature regulation, is made from two different types of metal strips that can expand and contract at different rates.
• Fire alarm system is designed with a circuit which is incomplete at room temperature.
• When the circuit is exposed to heat from a fire, the copper strip will expand faster than the steel strip, causing the strip to bend towards the contact point and complete the circuit system, resulting in an alarm ringing.
• Fuel tank trucks are often painted in bright colours such as white or silver to prevent heat absorption.
• Bright colours do not absorb a lot of heat.
• Evaporation of fuel is reduced in fuel tank trucks painted in bright colours.
• The ability of an object to absorb or radiate heat depends on the type and colour of its surface.