Module 9 - Electric Charge, Coulomb’s Law, Electric Field, Potential, and Potential Energy Web Page

Question 1

four identical (in size) metal spheres have charges of qa= -8uC, qb= -2uC, qc= 5uC, and qd=12uC. two of the spheres are brought together so that they are in contact. they are then seperated and are found to have identical final charges of 5uC. which two spheres are brought into contact?

Answer 1

B and D.

q1+q2/2 = -2+12/2 = 5uC

Question 2

object A has a charge of 5 and object B has a charge of 10. a third object, C, has an unknown charge. if object A exerts a force F on C what is the magnitude of the force of object B on C?
(same separation)

Answer 2

2F

reason: B is double A

Question 3

two uniformly charged spheres with net positive charges. charge on right sphere is 3 times as large as the charge on the left sphere. what are the magnitudes and directions of electric forces on the spheres?

Answer 3

opposite directions, same magnitude

Question 4

object A has a charge of 2uC and object B has a charge of 6uC.

Answer 4

Fab=-Fba

reason: like charges repel each other

Question 5

a test charge of 3uC is at a point P where the electric field due to other charges is directed to the right and has a magnitude of 4x10^6 N/C. if the test charge is replaced with a -3uC charge, the electric field at P;

Answer 5

remains the same, electric field is not affected by test charge

Question 6

T or F:
the electric force on the proton is greater in magnitude than the electric force on the electron, but in the opposite direction.
(proton and electron in identical electric field)

Answer 6

false. force that a charge feels in electric field is equal to the product of the charge and the field

Question 7

T or F:
the magnitude of the acceleration of the electron is greater than that of the proton.
(proton and electron in identical electric field)

Answer 7

true. net force, equal to charge times field, is equal to mass x acceleration. mass of proton is 2000 x of electron.

Question 8

two uniformly charged spheres with net positive charges. charge on right sphere is 3 times as large as the charge on the left sphere. what are the magnitudes and directions of the electric field vectors created by one sphere at the location of the other sphere?

Answer 8

left sphere has three times the magnitude than right sphere, opposite directions

Question 9

point A is close to an electron. point B is further from the electron. points A and B and the electron are along a straight line.

Answer 9

the field is stronger at point A than B and its directed from B to A

Question 10

if an electron (neglect the gravitational force from its mass) is released from rest in a uniform electric field, the electric potential energy of the charge-field system;

Answer 10

decreases.

electron accelerates, picks up speed, gains kinetic energy and the total energy is constant

Question 11

an electron, initially at rest, accelerates through a potential difference of 1 V, gaining kinetic energy KEe, while a proton, also initially at rest, accelerates through a potential difference of -1 V, gaining kinetic energy KEp, what relationship holds?

Answer 11

KEe=KEp
magnitude of charge moves through same magnitude of potential difference with both charges losing same amount of potential energy, total energy remains constant.

Question 12

the electric potential at two points in space is; V1=200volts and V2=300volts. what is always true for moving a point charge from 1 to 2?

Answer 12

the work done by the electric force exerted on q in moving it from point 1 to 2 is ;
W=-q(100V)

Question 13

A and B are both points on an equipotential surface. what is the potential difference between point A and B?

Answer 13

it is zero.