Physics Test Notes

Topics: Electric charge, Magnetic field, Electric current Pages: 14 (2881 words) Published: October 18, 2012
Society has become increasingly dependent on electricity over the last 200 years Random Keywords:
Independent Variable: variable that is changed

Dependent Variable: thing that changes with independent variable, it is what you measure

Control Variables: variable held constant for reference

Validity or valid: the extent to which a measurement accurately reflects the concept, which is intended to measure

Accuracy: how close your measurement or results are to the true value

Reliability: the extent to which a measurement yields consistent stable and uniform results over repeated observations or measurements.

Domestic energy and how it has changed
* The first sources of electrical energy were batteries, which provided low voltage DC power.

* Electromagnetism was discovered in the 19th century, which ultimately leads to the ability to generate electricity, and also to be able to distribute it over wide areas. Thomas Edison in New York in opened the first public electricity utility 1882-marking the first time that electricity was available for domestic and industrial use.

Impacts of the changes in sources of energy

* The use of coal has had a particularly large impact on our society * Coal could burn hot fires which made steel
* Steel was one of the factors that lead to the industrial revolution * Coal lead to the development of the steam engine
* Pollution and global warming was created

The production of electricity

* In 1831, Michael Faraday discovered electromagnetic induction, which lead to the development of the electrical generator * The generator consists of a rotating coil or wire in a magnetic field * Most power stations burn fuel to obtain this energy.

* Nuclear Power stations, hydroelectric power station, wind power, tidal energy are used to save non renewable energy.

* Electrostatic is the study of bodies with stationary electrical charges Materials that can be charges are: Ebonite rubbed with fur, Glass rubbed with silk, Perspex rubbed with wool.

Two kinds of charge
* There is a positive and a negative charge
Conservation of energy
* An atom consists of a nucleus of positive protons and neutral neutrons, surrounded by a cloud of orbiting negatively charged electrons. Electrons and protons have the same magnitude of charge but are of opposite sign * When two objects are rubbed together, the object that becomes negatively charged has an excess of electrons and the body that is positively charged has a deficiency of electrons Quantisation of electric energy

* Electric charge exists as discrete “packets”
* Q=NE where N is the some integer, e is the charge of an electron * The charge of a single electron e is e=1.602x10^-19C, where the Coulomb (C) is the unit of charge * Eg: determine 10 electrons= 10 x 1.602.10^19

Outline 4 properties of electric charge:
* unlike charges attract
* like charges repel
* charge is conserved
* charge is quantized.

Coulombs Law
Coulomb’s law is establishing the fundamental law of electric force between two stationary, charged particles. Various experiments show the following properties of an electric force

* The force is inversely proportional to the square of the separation (r) between two particles and is directed along the line joining the particles. (F inversely proportional r2)

* The force is proportional to the product of the charges q1 and q2 on the two particles. (F proportional to q1q2)

* The force is attractive if the charges are of opposite sign and repulsive if the charges have the same sign. (if k has an opposite sign to the Force then it attracts, visa versa)

From these experiments, we can deduce the magnitude of electric force between two charges

F = kq1q2
F = kq1q2

* Where k is a constant called coulomb constant
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