Physics 113 Exam #2

Which one of the following quantities is equivalent to 1 ohm?

1 V/A

Two identical small charged spheres are a certain distance apart, and each one initially experiences an electrostatic force of magnitude F due to the other. With time, charge gradually diminishes on both spheres by leaking off. When each of the spheres has lost half its initial charge, what will be the magnitude of the electrostatic force on each one?

1/4 F

An ideal parallel-plate capacitor has a capacitance of C. If the area of the plates is doubled and the distance between the plates is halved, what is the new capacitance?

4C

The length of a certain wire is kept same while its radius is doubled. What is the new resistance of this wire?

It is reduced by a factor of 4

Three identical capacitors are connected in a series across a potential source (battery). If a charge of Q flows into this combination of capacitors, how much charge does each capacitor carry?

Q

The lamps in a string of decorative lights are connected in parallel across a constant-voltage power source. What happens is one lamp burns out? (Assume negligible resistance in the wires leading to the lamps)

The brightness of the lamps will not change appreciably

A hydrogen nucleus, which has a charge +e, is situated to the left or 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

Consider two copper wires of equal length. One wire has twice the cross-sectional area of the other. How do the resistances of these two wires compare?

The thicker wire has one half the resistance of the thinner wire

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 the move toward each other?

Their kinetic energy keeps increasing Their electric potential energy keeps decreasing

An capacitor consists of two large parallel plates of area A separated by a very small distance d. This capacitor is connected to a battery and charged until its plates carry charges +Q and -Q, and then disconnected from the battery. If the separation between the plates is now doubled, the potential difference between the plates will

double

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

increases

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

is repelled by the sphere

As an electron moves in the direction the electric field lines

it is moving from high potential to low potential and gaining electrical potential energy

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

it remains the same

When a current flows through a metal wire, the moving charges are

only electrons

A capacitor C is connected in series with a resistor R across a battery and an open switch. If a second capacitor of capacitance 2C is connected in parallel to the first one, the time constant of the new RC circuit will be

three times as large as before