a force or attraction or repulsion is associated with charge

1. Electric Fields and Forces • a force or attraction or repulsion is associated with charge

2. Electric Fields and Forces From our work in Electricity, we have seen how Thompson and Goldstein discovered the electron and proton and how Millikan measured the charge of an electron (the elementary charge). We have also seen how simple experiments with electroscopes, plastic rods rubbed with wool and Van de Graaf generators suggest that • there are two types of charge • charge can be induced • a force or attraction or repulsion is associated with charge However, our experiments have only been qualitative (using data that has no quantity or number).In the 1780s Charles Augustin de Coulomb conducted quantitative experiments to measure the amount of the force associated with charge.

3. He did this by constructing a torsion balance. By bringing two charge spheres together he could determine the size of the associated force by measuring the size of the deflection on the torsion balance. Torsion balance video. Homemade torsion balance video.

4. Here is an experiment that shows some data similar to Coulomb’s.Whys is there a mirror in the apparatus?

5. Coulomb found that the force, whether repulsive or attractive, between two charges q1 and q2 a distance r apart was proportional to the product of the two charges, and inversely proportional to the square of the distance between them. This can be expressed by the simple equation below, where k is the proportionality constant and is given by 9 x 109 Nm2C-2. k can also be expressed in terms of the permittivity of a vacuum, = 8.85 x 10-12C2N-1m-2.

6. http://hyperphysics.phy-astr.gsu.edu/hbase/forces/isq.html

9. It is often very difficult to use Coulomb’s law because the force may originate from many charges spread around on a conductor. However, it is possible to measure or calculate the electric field. Just as the gravitational field (g) is the force on 1 kg, the electric field (E) is the force on 1 coulomb (C). Electric Field Lines video

10. http://hyperphysics.phy-astr.gsu.edu/hbase/electric/equipot.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/electric/equipot.html#c1

14. Electric Potential (V) - work done per unit charge moving a small positive test charge in from infinity to a point in an electric field. There is a deep connection between electric potential and electric field. In other words, field strength is the gradient of electric potential

15. The E-r and V-r graphs below show the relation clearly. The gradient of the V-r graph is negative. So the negative of its gradient gives a positive value for E in the E-r graph. http://www.a-levelphysicstutor.com/field-elect-1.php