Lecture 10

Readings

http://umdberg.pbworks.com/w/page/68392856/Electric%20field%20%282013%29

http://umdberg.pbworks.com/w/page/73084562/Making%20sense%20of%20the%20idea%20of%20field%20%282013%29

Electric Field

• Force of 2 "source charges" on "test charge"

• If all are positive:

• Have to keep track of directions

  • Aka, add vectors
  • So net force direction would be:

• Thing in parenthesis is $\stackrel{\rightharpoonup }{E}$$\overset{⇀}{E}$ , is the electric field

• $\stackrel{\rightharpoonup }{E}$$\overset{⇀}{E}$ is a function of location
• ${\hat{r}}_0$$\hat{r}_0$ is the vector from the origin to that location

• The value of $\stackrel{\rightharpoonup }{E}$$\overset{⇀}{E}$ at that location depends on all other source charges and their locations
• It does not depend on the magnitude of $q_0$$q_0$

• You can image $\stackrel{\rightharpoonup }{E}$$\overset{⇀}{E}$ at other places due to $q_1$$q_1$ and $q_2$$q_2$ :

• Old $E$$E$ ( before putting electrons ) is still good
• $E$$E$ at point 1 = $\frac{75N}{C}$$\frac{75 N}{C}$ to $N\ast E$$N *E$
• If I put an electron there, how much force does it feel?

• This is like imagining that $q_0$$q_0$ is moved to other locations

• $\stackrel{\rightharpoonup }{E}$$\overset{⇀}{E}$ can be calculated at every point in 3-D space.

  • It depends only on the locations of $q_1$$q_1$ and $q_2$$q_2$ , and the magnitude of charge on $q_1$$q_1$ and $q_2$$q_2$

• There is a single $\stackrel{\rightharpoonup }{E}$$\overset{⇀}{E}$ vector at every point in space

• It does not depend on $q_0$$q_0$

• If you put a $q_0$$q_0$ at a point in space, it feels the force: ${\stackrel{\rightharpoonup }{F}}_{q_0}^{net}=q_0\ast {\stackrel{\rightharpoonup }{E}}^{net}$$\overset{⇀}{F}^{net}_{q_0} = q_0 * \overset{⇀}{E}^{net}$

  • $q_0$$q_0$ can be any amount of charge, 1 Coulomb, or $1.6\ast {10}^{-19}C$$1.6 *10^{-19} C$

A point charge doesn't exert a force on itself

Multiple Choice