Chapter 11 : Heat and Electricity
A form of energy that is transferred by a difference in temperature.
Science defines heat as the flow of energy from a warm object to a cooler object
Energy decreases as heat passes from a warm body with higher temperature to a cold body with lower temperature.
Transfer of energy from one system to another by a difference of temperature.
It cannot be treated as a substance, because it may be transformed into something that is not a substance.
Heat transfer is classified into various mechanisms:
Topics covered in this snack-sized chapter:
Convection is the transfer of heat from one place to another by the movement of fluids
Convection is usually the way of heat transfer in gases and liquids.
Radiation is the generation of hot waves from substances whose temperature is greater than zero.
Thermal radiation includes the visible light and infrared light.
Example: Heat emitted by a light bulb.
Conduction is the flow of heat from the body itself. It is intermolecular transfer of heat.
By conduction, as well as by radiation, heat flows from a body at a higher temperature to a body at a lower temperature.
Substances which allow heat and electricity to pass through them are Conductors.
Substances which don’t allow heat and electricity to pass through them are Insulators.
Metals are generally good conductor of heat and electricity. Nonmetals do not allow heat and electricity to pass through them.
Silver, Copper, Gold, Iron are best conductors of heat and electricity.
Some metals such as lead, aluminum are poor conductors of heat and electricity but they are not insulators.
Wood, Rubber, Plastic and glass are the best insulators. They do not pass electricity from them.
Melting and boiling of conductors are very high.
Melting point of insulators is very low.
Electricity is a form of energy produced by the movement of electrons.
“Electric energy" is energy derived from electricity.
Electric current – A movement or flow of electrically charged particles
Electric field – An influence produced by an electric charge on other charges
Circuit – Closed path for electricity to flow from one place to another.
Electric potential – The capacity of an electric field to do work on an electric charge
Electric current is a flow of electric charge through a conductive medium.
Current is a rate of flow of negatively-charged particles, called electrons.
- Electron flow is in one direction and at a constant rate.
Voltage - Potential difference across two terminals in a circuit “across variable.”
We can’t always generate electricity when it is needed so Batteries are devices that store electrical energy in chemical form and are very important.
When we connect batteries with any electrical thing circuit completes and electricity starts flowing.
As we know energy can change from one form to another in batteries, chemical energy change into electrical energy.
In generators, mechanical energy changes into electrical energy.
Generators use kerosene, petrol and coal as fuel for changing mechanical energy into electrical energy.
Magnets attract, or pull, some kinds of metal objects. Stronger magnets exert a greater pull on the objects they attract.
Sometimes it would be useful if you could "turn off" a magnet when you did not want it to attract objects. That is what an electromagnet can do.
Electric current can act like a magnet it attracts objects made of certain metals, such as iron.
When electric current flows through a wire, it generates a magnetic field.
- Electron flow changes direction in regular, repeated cycles.