Electricity

The figure shows four Gaussian surfaces surrounding a distribution of charges. (a) Which Gaussian surfaces have an electric flux of +q/εo through them? (b) Which Gaussian surfaces have no electric flux through them

(a) Surface B (b) Surface C

A small charged plastic ball is vertically above another charged small ball in a frictionless test tube as shown in the figure. The balls are in equilibrium a distance d apart. If the charge on each ball is doubled, the equilibrium distance between the balls in the test tube would become A) d. B) 2d. C) 4d. D) 8d. E) d/4.

2d

A hydrogen atom consists of a proton and an electron. If the orbital radius of the electron increases, the electric potential energy of the electron due to the proton A) increases. B) decreases. C) remains the same. D) depends on the zero point of the potential

A

A negatively-charged rod is brought close to (but does not touch) two neutral spheres that are in contact with each other but insulated from the ground. If the two spheres are then separated, what kind of charge will be on the spheres? A) The sphere near the charged rod becomes positive and the other one becomes negative. B) The sphere near the charged rod becomes negative and the other one becomes positive. C) The spheres do not get any charge. D) Both spheres become negative. E) Both spheres become positive.

A

A solid aluminum cube rests on a wooden table in a region where a uniform external electric field is directed straight upward. What can we say concerning the charge on the top surface of the cube? A) The top surface is charged positively. B) The top surface is charged negatively. C) The top surface is neutral. D) The top surface's charge cannot be determined without further information

A

If the result of your calculation of a quantity has SI units kg ∙ m/(s2 ∙ C), that quantity could be A) an electric field strength. B) a dielectric constant. C) an electric potential difference. D) a capacitance E) an electric potential energy.

A

A conductor is placed in a steady external electric field. Which of the following statements are correct for this situation? (There could be more than one correct choice.) A) The electric field is zero inside the conductor. B) All the free electrons go to the surface of the conductor. C) The surface of the conductor is neutral. D) The electric field just outside the surface of the conductor is perpendicular to the surface. E) None of the above statements are correct.

A, B, D

Two protons are fired toward each other in a particle accelerator, with only the electrostatic force acting. Which of the following statements must be true about them as they move closer together? (There could be more than one correct choice.) A) Their electric potential energy keeps increasing. B) Their kinetic energy keeps increasing. C) Their electric potential energy keeps decreasing. D) Their kinetic energy keeps decreasing. E) Their acceleration keeps decreasing. Answer: A, D

A, D

1) Electrically neutral objects cannot exert an electrical force on each other, but they can exert a gravitational force on each other. A) True B) False

B

An electron and a proton are released simultaneously from rest and start moving toward each other due to their electrostatic attraction, with no other forces present. Which of the following statements are true just before they are about to collide? (There could be more than one correct choice.) A) They are closer to the to the initial position of the electron that to the initial position of the proton. B) They are closer to the to the initial position of the proton that to the initial position of the electron. C) They are at the midpoint of their initial separation. D) They both have the same speed. E) The electrostatic force on the proton is greater than the electrostatic force on the electron.

B

Two uncharged metal spheres, #1 and #2, are mounted on insulating support rods. A third metal sphere, carrying a positive charge, is then placed near #2. Now a copper wire is momentarily connected between #1 and #2 and then removed. Finally, sphere #3 is removed. In this final state A) spheres #1 and #2 are still uncharged. B) sphere #1 carries positive charge and #2 carries negative charge. C) sphere #1 carries negative charge and #2 carries positive charge. D) spheres #1 and #2 both carry positive charge. E) spheres #1 and #2 both carry negative charge.

B

A proton and an electron are released from rest, with only the electrostatic force acting. Which of the following statements must be true about them as they move toward each other? (There could be more than one correct choice.) A) Their electric potential energy keeps increasing. B) Their kinetic energy keeps increasing. C) Their electric potential energy keeps decreasing. D) Their kinetic energy keeps decreasing. E) Their acceleration keeps decreasing.

B,C

Two protons are released from rest, with only the electrostatic force acting. Which of the following statements must be true about them as they move apart? (There could be more than one correct choice.) A) Their electric potential energy keeps increasing. B) Their kinetic energy keeps increasing. C) Their electric potential energy keeps decreasing. D) Their kinetic energy keeps decreasing. E) Their acceleration keeps decreasing.

B,C,E

A dielectric material such as paper is inserted between the plates of a capacitor as the capacitor holds a fixed charge on its plates. What happens to the electric field between the plates as the dielectric is inserted? A) There is no change in the field. B) The field becomes stronger. C) The field becomes weaker. D) The field reduces to zero

C

As an electron moves in the direction the electric field lines A) it is moving from low potential to high potential and gaining electric potential energy. B) it is moving from low potential to high potential and losing electric potential energy. C) it is moving from high potential to low potential and gaining electric potential energy. D) it is moving from high potential to low potential and losing electric potential energy. E) both its electric potential and electric potential energy remain constant.

C

Gaussian surfaces A and B enclose the same positive charge +Q. The area of Gaussian surface A is three times larger than that of Gaussian surface B. The electric flux through Gaussian surface A is A) nine times larger than the flux of electric field through Gaussian surface B. B) three times larger than the flux of electric field through Gaussian surface B. C) equal to the flux of electric field through Gaussian surface B. D) three times smaller than the flux of electric field through Gaussian surface B. E) unrelated to the flux of electric field through Gaussian surface B.

C

If the result of your calculation of a quantity has SI units kg ∙ m2/(s2 ∙ C), that quantity could be A) an electric field strength. B) a dielectric constant. C) an electric potential difference. D) a capacitance E) an electric potential energy.

C

A proton is accelerated from rest through a potential difference V0 and gains a speed v0. If it were accelerated instead through a potential difference of 2V0, what speed would it gain? A) 8v0 B) 4v0 C) 2v0 D) v0 radical 2

D

If the result of your calculations for a quantity has SI units of C2 ∙ s2/(kg ∙ m2), that quantity could be A) an electric potential difference. B) a dielectric constant. C) an electric field strength. D) a capacitance. E) an electric potential energy.

D

If two objects are electrically attracted to each other, A) both objects must be negatively charged. B) both objects must be positively charged. C) one object must be negatively charged and the other object must be positively charged. D) the objects could be electrically neutral. E) None of the above statements are absolutely true.

D

Which of the following will increase the capacitance of a parallel-plate capacitor? (There could be more than one correct choice.) A) a decrease in the plate area and an increase in the plate separation B) a decrease in the potential difference between the plates C) an increase in the potential difference between the plates D) an increase in the plate area and a decrease in the plate separation E) an increase in the charge on the plates

D

In outer space, a positive charge q is released near a positive fixed charge Q, as shown in the figure. As q moves away from Q, what is true about the motion of q? (There may be more than one correct choice.) A) It will move with decreasing speed. B) It will move with constant acceleration. C) It will move with increasing acceleration. D) It will move with decreasing acceleration. E) It will move with increasing speed.

D, E

Which statements must be true about the surface of a charged conductor in which no charge is moving? (There could be more than one correct choice.) A) The electric field is zero at the surface. B) The electric potential of the surface is zero. C) The electric field is constant at the surface. D) The electric potential is constant over the surface. E) The electric field is perpendicular to the surface.

D, E

As a proton moves in a direction perpendicular to the electric field lines A) it is moving from low potential to high potential and gaining electric potential energy. B) it is moving from low potential to high potential and losing electric potential energy. C) it is moving from high potential to low potential and gaining electric potential energy. D) it is moving from high potential to low potential and losing electric potential energy. E) both its electric potential and electric potential energy remain constant.

E

If the electric potential at a point in space is zero, then the electric field at that point must be A) negative. B) zero. C) uniform. D) positive. E) impossible to determine based on the information given.

E