CP2 test 2

You are given an aluminum bar of dimensions 10 cm x 4 cm x 1 cm and asked to attach leads to it in order to make a resistor. If you want to achieve the smallest possible resistance, you should attach the leads to the opposite faces that measure

10 cm x 4cm

Two ideal parallel-plate capacitors are identical in every respect except that one has 3 times the plate area of the other one. If the smaller capacitor has a capacitance C, the larger one has capacitance

3C

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

When a dielectric material is introduced between the plates of a parallel-plate capacitor and completely fills the space, the capacitance increase by a factor of 5. What is the dielectric constant of the material that was introduced?

5

You are given an aluminum bar of dimensions 6 cm x 2 cm x .5 cm and asked to attach leads to it in order to make a resistor. If you want to achieve the smallest possible resistance, you should attach the leads to the opposite faces that measure

6 cm x 2 cm

Consider two gold wires of equal cross-sectional area. One wire is 4 times as long as the other. how do the resistivities of these two wires compare?

Both wires have the same resistivity

A parallel plate capacitor has horizontal plates. The top plate has a positive and the bottom plate has a negative charge. What is the direction of the electric field in the capacitor?

Down

Which of the following changes will increase the capacitance of a parallel-plate capacitor? (there could be more than one correct choice.)

Introduce a dielectric material between the plates; Decrease the separation between the plates

The length of a certain wire is doubled and at the same time its radius is also doubled. What is the new resistance of this wire?

It is 1/2 as large

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

It is 2 times as large

As a proton moves in the direction the electric field lines

It is moving from high potential to low potential and losing electric potential energy

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 O, what is true about the motion of q? (there may be more than one correct choice.)

It will move with decreasing acceleration; It will move with increasing speed

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?

The fields becomes weaker

Two tiny beads are 25 cm apart with no other charges or fields present. Bead A carries 5 uC of charge and bead B carries 1 uC. Which on of the following statements is true about the magnitudes of the electric forces on these beads?

The force on A is exactly equal to the force on B

Copper wire #1 has a length L and a radius b. Copper wire #2 has a length 2L and a radius 2b. Which statement about the resistance across the ends of the wires is true?

The resistance of wire #1 is twice as high as that of wire #2

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 charges rod becomes positive and the other one becomes negative

A solid copper cube rests on a wooden table in a region where a uniform external electric field is directed straight downward. What can we say concerning the charge on the top surface of the cube?

The top surface is charged negatively

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?

Their electric potential energy keeps increasing

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.)

Their kinetic energy keeps increasing; Their electric potential energy keeps decreasing; Their acceleration keeps decreasing

X and Y are two initially uncharges metal spheres on insulating stands, and they are in contact with each other. A positively charges 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

When a current flows through an ionic liquid such as salty water, the moving charges are

both positive and negative ions

A parallel-plate capacitor consists of a set of two parallel plates of area A separated by a distance d. This capacitor is connected to a battery that maintains a constant potential difference across the plates. A slab of a dielectric material is inserted in the region between the plates and completely fills it. What changes would you observe as the dielectric is inserted? (there could be more than one correct choice.)

both the charge on the plates of the capacitor and its capacitance would change

A proton and an electron are separately placed at rest in the same uniform field. What can be said about the energy of each after they are released?

electric potential energy of both decreases, and kinetic energy of both increases

The electron-volt is a unit of

energy

A plastic rod is charged by rubbing with 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

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

it remains the same

Two uncharges metal spheres, #1 and #2, are mounted on insulting 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 is removed. In this final state

sphere #1 carries positive charge and #2 carries negative charge

A capacitor is connected to a battery and charged to Q. A dielectric is inserted in the capacitor while it is connected to the battery. Which of the following is true?

the capacitance and charge increase

A capacitor is connected to a battery until it has charge Q. It is then disconnected from the battery maintaining its charge. A dielectric material is introduced between the plates. Which of the following is true?

the capacitance increases and the potential difference decreases

A capacitor initially has a charge Q on it. As the charge is reduced what happens to the capacitance and the electric field between the plates?

the capacitance is constant and the electric field decreases

Two tiny beads are 6 cm apart with no other charges or fields present. Bead A carries 2.5 uC of charge and bead B carries 100 uC. Which on of the following statements is true about the magnitudes of the electric forces on these beads?

the force of A is exactly equal to the force on B

An electron is initially moving to the right when it enters a uniform electric field directed upwards, as shown in the figure. Which trajectory (X, Y, Z or W) will the electron follow in the field?

trajectory Z

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?

v0squareroot 2