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 = kQ1Q2/r2
Where K = 1/4πE
E = permittivty of material between charges.
r = is the distance between the charges.
- The force on Q1 is equal and opposite to the force on Q2.
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?
- 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/r2
- 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:
V is the potential diffirence between the plates and d is the distance between them.