8/7/2019 15.1-15.3 Wksht 2010-2011

1/5

IB PHYSICS SL GOHS

15.1-15.3 Worksheet: Coulombs Law

8/7/2019 15.1-15.3 Wksht 2010-2011

2/5

9. Two identical conducting spheres are placed with their centers 0.30 mapart. One is given a charge of 12 10 9 C, the other a charge of 18 10 9

C. (a) Find the electrostatic force exerted on one sphere by the other. (b) Thespheres are connected by a conducting wire. Find the electrostatic forcebetween the two after equilibrium is reached. (2.2x10 -5 N;

9.0x10 -7 N)10. Calculate the magnitude anddirection of the Coulomb force on each

of the three charges shown to the right.(46.7 N; 157 N; 111 N)13. Three point charges are located at the corners of anequilateral triangle as in the figure to the left. Calculatethe net electric force on the 7.00- C charge. (0.872 N 30 o

below the + x -axis)

2. Conducting shoes are worn toavoid the build up of a staticcharge on them as the wearer

walks. Rubber soled shoes acquirea charge by friction with the floorand could discharge with a spark,possibly causing an explosiveburning situation, where theburning is enhanced by theoxygen.

4. Electrons are more mobile thanprotons and are more easily freedfrom atoms than are protons.

6. No. Object A might have a charge

opposite in sign to that of B,but it also might be neutral. In thislatter case, object B causesobject A to be polarized, pullingcharge of one sign to the nearface of A and pushing an equalamount of charge of theopposite sign to the far face. Thenthe force of attractionexerted by B on the inducedcharge on the near side of A isslightly larger than the force of

repulsion exerted by B on theinduced charge on the far side of A. Therefore, the net force

8/7/2019 15.1-15.3 Wksht 2010-2011

3/5

ANSWERS

15.9 (a) The spherically symmetric charge distributions behave as if all charge waslocated at the centers of the spheres. Therefore, the magnitude of the

attractive force is

( ) ( )( )

9 921 2 9 5

22 2

12 10 C 18 10 CN m8.99 10 2.2 10 NC 0.30 m

ek q qFr

= = =

(b) When the spheres are connected by a conducting wire, the net charge9

1 2 6.0 10 Cnetq q q= + = will divide equally between the two identical

spheres. Thus, the force is now

( ) ( )

( )

22 929

22 2

6.0 10 C2 N m8.99 10C 4 0.30 m

e netk qFr

= =

or79.0 10 N (repulsion)F =

8/7/2019 15.1-15.3 Wksht 2010-2011

4/5

8/7/2019 15.1-15.3 Wksht 2010-2011

5/5