PHY112 Exam I

Four point charges Q of equal magnitude and sign are arranged on three of the corners of the square of side d as shown in the figure Which one of the arrows shown represents the net force acting on the charge at the upper right hand corner of the square

D

T/F A dielectric material such as paper is inserted between the plates of a capacitor as the capacitor holds a fixed charged on its plates. The electric field between the plates as the dielectric is inserted will become stronger

False

T/F In electrostatic equilibrium charges are moving

False

T/F The electric field inside of a charged conductor is not zero

False

T/F Two electrons released from rest will move toward each other

False

T/F In metal the positive charges are what moves

False

Two point charges, Q1 and Q2, are separated by a distance R. If the magnitudes of both charges are doubled and their separation is also doubled, what happens to the electrical force that each charge exerts on the other one?

It remains the same.

Two stationary point charges q1 and q2 are shown in the figure along with a sketch of some field lines representing the electric field produced by them. What can you deduce from the sketch

) q1 is negative and q2 is positive; the magnitude of q1 is less than the magnitude of q2.

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

2d

The force of attraction that a -40.0 μC point charge exerts on a +108 μC point charge has magnitude 4.00 N. How far apart are these two charges? (k = 1/4πε0 = 8.99 × 109 N ∙ m2/C2)

3.12 m

Two electrons are apart at closest approach. What is the magnitude of the maximum electric force that they exert on each other? (e = 1.60 × 10-19 C, k = 1/4πε0 = 9.0 109 N ∙ m2/C2)

5.8 × 10-25 N

Two very small plastic balls of equal mass are released from rest. One of them carries +10 µC of excess charge and the other one carries +1µC of charge. No other charges or fields are present. Which of the following statements are true about them as they move away from each other?

The balls always have accelerations of equal magnitude. The speed of the balls keeps increasing.

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.)

The electric field is zero inside the conductor. All the free electrons go to the surface of the conductor. The electric field just outside the surface of the conductor is perpendicular to the surface.

A hydrogen nucleus, which has a charge +e, is situated to the left of a carbon nucleus, which has a charge +6e. Which statement is true?

The electrical force experienced by the hydrogen nucleus is to the left, and the magnitude is equal to the force exerted on the carbon nucleus.

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?

The sphere near the charged rod becomes positive and the other one becomes negative.

Three equal charges +Q are at three of the corners of a square of side d. A fourth charge +Q of equal magnitude is at the center of the square as shown in the figure Which one of the arrows shown represents the net force acting on the charge at the center of the square?

B

Three equal negative point charges -q are placed at three of the corners of a square of side d as shown in the figure. Which one of the arrows shown represents the direction of the net electric field at the vacant corner of the square?

B

T/F A dielectric constant always increases the capacitance of a capacitor

True

T/F Drift speed is how fast the atoms move

True

T/F The electric field inside of charged parallel plate capacitor is uniform

True

T/F The length of a certain wire is kept the same while its radius is doubled. The resistance of this wire does change

True

T/F Two protons are released from rest, with only the electrostatic force acting, their velocity will keep increasing

True

X and Y are two initially uncharged metal spheres on insulating stands, and they are in contact with each other. A positively charged rod R is brought close to X as shown in part (a) of the figure. Sphere Y is now moved away from X, as shown in part (b). What are the final charge states of X and Y?

X is negative and Y is positive.

The electric field at point P due to a point charge Q a distance R away from P has magnitude E. In order to double the magnitude of the field at P, you could

double the charge to 2Q.

A plastic rod is charged up by rubbing a wool cloth, and brought to an initially neutral metallic sphere that is insulated from ground. It is allowed to touch the sphere for a few seconds, and then is separated from the sphere by a small distance. After the rod is separated, the rod

is repelled by the sphere.

A negatively-charged plastic rod is brought close to (but does not touch) a neutral metal sphere that is connected to ground. After waiting a few seconds, the ground connection is removed (without touching the sphere), and after that the rod is also removed. The sphere is now

positively charged.

) Four tiny charged particles (two having a charge +Q and two having a charge -Q) are distributed on the x- and y-axes as shown in the figure. Each charge is equidistant from the origin. In which direction is the net electric field at the point P on the y-axis?

upwards and towards the left