Name some basic rules of charges and electric fields

- Electric charge,Q, is measured in coulombs(C) and can be either positive or negative.- Opposite charged particles attract each other.Like charges repel.- If a charged objet is placed in an electric field, then it will experience a force. - Any object with charge has an electric field around it.

What is the equation for Coulomb's law?

F = kQ_{1}Q_{2}/r^{2}

Where K = 1/4πE

E = permittivty of material between charges.

r = is the distance between the charges.

- The force on Q_{1} is equal and opposite to the force on Q_{2}.

What is the definition of electric field strength, E?

Electric field strength, E is defined as the force per unit positive charge - the force that a charge of 1+ C would experience if it was placed in the electric field.

What is the equation for electric field strength?

E=F/q

- F is the force on a charge q.

- E is a vector pointing in the direction that a positive charge would move.

Draw the field lines around a positive charge and the field lines around a negative charge.

What is the equation for electric field strength at diffirent points along a radial field?

E = kQ/r^{2}

- r is the distance from a point charge.

Draw the graph of E against r. (Where r is the distance from a point charge Q.)

- State what the relationship is between the two variables.

- What the area under the graph is.

- The relationship between E and r is an inverse square one.

- The area under the graph is the electric potential.

What is electric potential energy?

The work that would need to be done to move a small charge,q, from infinity to a distance r away from a point charge, Q.

What is the equation for electric potential energy.

E = kQq/r

- Q is a point charge and q is another charge.

- In a repulsive force field(Q and q are both positive) you have to do work against the repulsion to bring q closer to Q. The charge q gains potential energy as r decreases.

- In an attractive field the charge q gains potential energy as r increases.

Draw the graph of the electric potential energy of a charge q when in a repulsive field and when in an attractive field at distances r from the source.

What is electric potential, V.

Electric potential, V, is electric potential energy per unit positive charge.

What is the equation for electric potential.

V = kQ/r

- V is measured in volts

- As with E, V is positive when the force is repulsive, and negative when the force is attractive.

Draw the graph of electric potential , V, against distance for a repulsive force.

- What does the gradient of the graph tell you?

The gradient of a tanget gives the field strength.

How can a uniform field be made?

A uniform field can be produced by connecting two parallel plates to the opposite poles of a battery.

How can the field strength, E, be calculated from a uniform field between two plates?

Field strength E is the same at all points between the two plates and is given by:

E= V/d

V is the potential diffirence between the plates and d is the distance between them.