Study notes, tips, worksheets, exam papers
All the things you need to do well in your studies
Lenz’s Law states that the direction of the induced e.m.f. and hence the induced current in a closed circuit, is always such that its magnetic effect opposes the motion or change producing the induced e.m.f.
(Memorise it! It is useful when trying to explain the effects caused by Lenz’s Law)
An electrostatic precipitator (ESP) is a device that removes particulate matter from exhaust gases using electrostatic forces. It is commonly used in industries such as power plants, cement factories and steel mills to control air pollution.
The basic principle of an ESP is to use an electric field to charge the solid particles in the gas stream, and then collect them on a charged surface.
1. The gas stream is first passed through a series of electrodes, which are typically made of metal wires or plates. These electrodes are charged with a high voltage, usually in the range of tens of thousands of volts.
2. As the gas stream passes through the electrodes, the solid particles in the gas become charged, either positively or negatively depending on the polarity of the electrodes. The charged particles are then attracted to an oppositely charged collection electrode, which is usually a flat metal plate or a series of plates.
3. As the particles collect on the collection electrode, they form a layer of solid deposits that can be removed periodically. This is done by rapping on the collection plates, which causes the solid deposits to fall into a hopper or other collection device.
Energy can be transferred from one store to another:
i) Mechanically (by a force acting over a distance)
Eg: a car moving up an inclined plane
(chemical potential energy –> gravitational potential energy)
ii) Electrically (by an electric current)
Eg: lighting up a bulb in an electric circuit
(chemical potential energy of battery –> light and heat energy of light bulb)
iii) By heating (due to a temperature difference)
Eg: a gas stove heating up a pot of water
(chemical potential energy of gas –> internal energy of water)
iv) By propagation of waves (both electromagnetic and mechanical)
Eg: a dipper producing surface water waves
(mechanical energy of dipper –> kinetic energy of water waves)
An energy store is a substance or a physical system that can store energy in various forms.
Some examples of energy stores are:
– batteries (chemical potential energy)
– a stretched spring (elastic potential energy)
– fuels (chemical potential energy)
– a dammed water body (gravitational potential energy)
– tidal waves (kinetic energy)
– radioactive isotopes (nuclear energy)
