A hydrogen atom is composed of a nucleus containing a single proton, about which a single electron orbits. The electrical force between the two particles is 2.3  greater than the gravitational force! If we adjust the distance separating the two particles, can we find a separation at which the electrical and gravitational forces are equal? 1) Yes, by moving the particles farther apart. 2) Yes, by moving the particles closer together. 3) No, at any distance.

3 meters +16  C+4  C Where is the net electric field between these two charges ZERO? d3 meters - d 0

4 discrete charges of magnitude, q, and the indicated signs, occupy the corners of a rectangle as shown. The direction of the electric field, E, at the point shown is: 1) up 2) left 3) right 4) down 5) other +q qq qq

4 discrete charges of magnitude, q, and the indicated signs, occupy the corners of a rectangle as shown. The direction of the electric field, E, at the point shown is: 1) up 2) left 3) right 4) down 5) other +q qq qq

4 discrete charges of magnitude, q, and the indicated signs, occupy the corners of a rectangle as shown. The direction of the electric field, E, at the point shown is: 1) up 2) left 3) right 4) down 5) other +q qq qq

 +

-q +2 q

-3q-3q

Proportionalities A B C D w x A zA z  ? 1.A/ w 2.A/ x 3.B/ x 4.C/ x 5.D/ x 6.D/ w y z

Proportionalities A B C D E F ACAC  ? 1.E/F 2.F/E 3.D/F 4.F/D 5.E/D 6.D/E

Proportionalities R A aA a  ? 1. R- r 2. R+ r 3. R 2 / r 2 4. R 2 / r 5. R/ r 6. r /R a A r

Proportionalities R A aA a  ? 1.  R/ r 2. R/  r 3. R 2 / r 2 4.  R 2 / r 5. R/ r 6. r 2 /R 2 a r A

The same proportionalities work for arc-lengths R S R s r  r S s