Topic 6 Fields and ForcesEdit
^{[1]} ^{[2]}
6.1 Gravitational Force and FieldEdit
6.1.1 State Newton's universal law of gravitationEdit
 Every single point mass attracts every other point mass with a force that is proportional to the product of their masses and is inversely proportional to the square of their separation

 G = universal gravitation constant (6.67 x 10^{11)}Nm^{2}kg^{2} determined by Henry Cavendish
 M = source mass (where the field is coming from)
 m = test mass (mass being affected by force, though it has a gravitational force on its own)
 r = the distance between the centres of each mass

6.1.2 Define gravitational field strengthEdit
A space where a small test mass feels a force due to its mass.
6.1.3 Determine the gravitational field due to one or more point massesEdit
 gravitational field can be shown using gravitational field lines
 gravitational field lines must be evenly dispersed around the point mass
 more lines indicates a greater field magnitude
6.1.4 Derive an expression for gravitational field strength at the surface of a planet, assuming all its mass is concentrated at the centreEdit
In other words, an equation that expresses gravitational field strength in terms of the distance away from the source must be found; a function g(r) that calculates the gravitational field strength when the distance away is known. This is because in the situation, we want to find the gravitational field strength when we know how far the surface is from the source.


 The m's cancel so:

6.2 Electric Force and FieldEdit
6.2.1 State two types of chargeEdit
 positive (+) = a deficiency of electrons
 negative () = an excess of electrons
6.2.2 State and apply The Law of Conservation of ChargeEdit
 The net charge of an isolated system is conserved. The charge stays constant.
 Charge can neither be created nor destroyed.
 Using this law, we can always predict how many positive and negative charges exist
6.2.3 Describe and Explain the difference in electrical properties of conductors and insulatorsEdit
 Conductors
 substances that allow electron to easily flow through them
 Examples: metal graphite
 Superconductor: a perfect conductor, all substances become superconductors at 0 Kelvin
 Insulator
 Substances that do not allow electrons to flow easily through them
 Examples: plastics, rubber
 There are no perfect insulators
6.2.4 State Coulomb's LawEdit
 The electric force between two charges are proportional to the product of their charges and inversely proportional to the square of the distance between them
 It acts along the line joining the two charges
 F = Force of electric charge attraction/repulsion
 q_{1} = source charge
 q_{2} = test charge
 r = distance between centre of charges
 k = coulomb constant (8.99 x 10^{9})Nm^{2}C^{2} in a vacuum
 In other media use where E_{0} is the permitivity constant of free space

6.2.5 Define electric field strengthEdit
 The force felt per unit charge by a small positive test charge at that point in the electronic field.

 Electric fields exist around charges and combinations of charges
6.2.6 Determine the electric field strength due to one or more point chargesEdit
6.2.7 Draw the electric field patterns for different charge configurationsEdit
 Need pictures
 Electric field always flows from positive to negative
6.3 Magnetic Force and FieldsEdit
6.3.1 State the moving charges give rise to magnetic fieldsEdit
 Oersted's basic principle of electromagnetism: moving charges produce a magnetic field
6.3.2 Draw magnetic field patterns due to currentsEdit
 charge moving through wire
 solenoid
 freely moving charge in a magnetic field
6.3.3 Determine the direction of the force on a charge moving in a magnetic fieldEdit
 Right Hand Rule #3
 fingers are magnetic field
 thumb is direction of velocity
 palm is force
 or Left Hand Rule (FBI rule)
 name fingers of your left hand with letters FBI, starting from thumb, and hold the three fingers so that there are right angles between each two.
 F (thumb) stands for force
 B (index finger) is the magnetic field direction
 I (middle finger) is the direction of current (same as that of velocity of positive charge and opposite to velocity of negative charge)
6.3.4. Define the magnitude and direction of a magnetic fieldEdit
 Magnetic field moves from north to south and is flipped within a magnet