Charged objects have an ELECTRIC FIELD around them - this is the region where they can attract or reel other charges.
- Charge is measured in Coloumbs (C).
- Objects placed in electric fields experience a force.
COULOMBS LAW: F = kQ1Q2/r² where k = 1 / 4πε
where ε = permittivity between charges. For free space, ε = 8.85 x 10^-12 C²N^-1N^-2
This is an inverse square law - the further apart the charges are, the weaker the forces between them.
Also, the force on Q1 is equal and opposite to the force on Q2.
Radial and Uniform Electric Fields
Figure 1 - RADIAL FIELD Figure 2 - UNIFORM FIELD
Electric Field Strength is force per unit charge E = F/Q
In a radial field E is inversely proportional to r² - to calculate the filed strength in a radial field combine Coloumb's Law and the above equation to get: E=kQ/r²
In a uniform field E is the same everywhere (E is uniform) E = V/d
CAPACITANCE is the amount of charge stored per volt C = Q/V and is measured in farads
Capacitors store energy
If the switch is flicked to A, the capacitor is charging - charges are deposited on one plate and the opposite charge is removed from the other plate. When switched to B, the capacitor discharges. You can find the energy stored in a capacitor by plotting a graph of V against Q and finding the area under the graph. This gives W = 1/2 QV.
Substitute Q=CV and you get: Q = 1/2CV² s4bst5t4te V=Q/C and you get W = Q²/2C