Physics II - Turning Point Questions Exam 2

Consider a uniformly negatively charged sphere. What is the sign of the energy of the system? Let the system have zero energy if all the charges were infinitely separated. A. positive B. negative C. zero

A. positive

In a region of space, the electric potential is constant and positive. What can be inferred about the electric field in the region? A. the electric field is zero B. the electric field is positive C. the electric field is negative D. nothing can be inferred about the electric field

A. the electric field is zero

Can you connect two resistors of resistance R in such a way that the resistance of the combination is R/2? A. Yes, if you connect them in series B. Yes, if you connect them in parallel C. No, it's not possible

B. Yes, if you connect them in parallel

Suppose you have a system consisting of a positive and negative charge. If you pull them apart, does the potential energy of the system increase or decrease? A. decrease B. increase C. can't tell/depends

B. increase

You bring a negatively charged object near an uncharged conductor. As a result, some parts of the conductor develop a net charge. Which parts? A. The surface B. The inside C. Both the surface and the inside D. Neither. There is no net charge anywhere on or in the conductor

A. The surface

You have two wires made of the same material, one twice the diameter of the other. The thicker wire will have... A. Half the resistance of the thinner wire B. One fourth the resistance of the thinner wire C. Twice the resistance of the thinner wire D. Four times the resistance of the thinner wire

B. One fourth the resistance of the thinner wire

A non-uniform radial charge distribution produces an electric field of E~ = Cr^2 rˆ for r > 5.0cm and E~ = 0 for r < 5.0cm, where C = 1700 N/C /m^2 is a constant. What is the potential difference between a point r = 10.0cm and the center of the distribution, ∆Vr,0? A. +0.50V B. +3.50V C. +1.25V D. +2.25V E. +2.3V

A. +0.50V

A hollow metal conductor has inner radius R and outer radius 2R. A charge Q is placed on the conductor. How much of this charge is on the inner surface of the conductor? There is no other net charge near the system. A. 0 B. Q C. -Q D. Q/2 E. Q/4

A. 0

The earth has a radius of 6.4 × 10^6m. Compute its capacitance if it was a perfect conducting sphere. A. 7.1 × 10^20F B. 7.1 × 10^−4F C. 7.2 × 10^17F D. You have to know the charge of the earth to calculate the capacitance.

B. 7.1 × 10^−4F

The relation E~ = E0~/κ where E~ is the field in the dielectric, κ is the dielectric constant, and E0~ is the applied field is A. true in all cases B. true only in high symmetry cases C. always false

B. true only in high symmetry cases

A region of space contains an electric field E~ = − γ x^3 xˆ where γ = 160 Nm^3/C . Compute the potential difference, ∆Vab (including the appropriate sign) between the point a = 1m and the point b = 2m along the x-axis A. +240V B. -240V C. +60V D. -60V

C. +60V

A parallel-plate capacitor has plate area A. A battery is used to charge the capacitor so that the magnitude of charge on each plate is Q, and then is disconnected. Initially, the capacitor has a plate separation of d. At this separation the capacitor contains energy U. The plates are then moved to a separation of 3d without disturbing the charge. What is the energy of the capacitor at this larger plate separation? A. U B. U/3 C. 3U D. U/9 E. 9U F. √ 3U G. U/√ 3

C. 3U

A dielectric slab with a dielectric constant, κ = 2, is placed in a uniform electric field that is parallel to the normal of the slab and has a magnitude of 12 N C . What is the magnitude of the field inside the dielectric? A. 0 B. 24 N/C C. 6 N/C D. 12 N C

C. 6 N/C

The parallel plates of a capacitor have area 0.0313 m^2 , and are separated by a 0.61-cm air gap. A potential difference of 18000 V is applied (which is the maximum that can be applied before the capacitor sparks, at that plate separation). What is the energy stored in the capacitor at that potential difference? A. 0.015J B. 4.1 × 10^−7J C. 7.4 × 10^−3J D. 7.4 × 10^−5J

C. 7.4 × 10^−3J

Suppose the electric field was not perpendicular to the surface of a conductor, what would happen? A. Nothing would happen if the field was not perpendicular to the conductor's surface B. The electric field would be larger inside the conductor than outside the conductor C. An electric current would flow along the surface of the conductor D. The surface atoms of the conductor would become insulating E. The resistance of the conductor would increase.

C. An electric current would flow along the surface of the conductor

Which of these is true of an equipotential surface? A. The electric field is zero at each point on the surface. B. The electric field is perpendicular to the surface normal at each point on the surface. C. The electric field is parallel to the surface normal at all points on the surface.

C. The electric field is parallel to the surface normal at all points on the surface.

Two light bulbs are rated 60W and 100W, respectively, when connected to the same voltage. The 100W bulb will have... A. The largest current and the largest resistance B. The smallest current and the smallest resistance C. The largest current and the smallest resistance D. The smallest current and the largest resistance

C. The largest current and the smallest resistance

On which of the following does the capacitance of a capacitor depend? A. The charge on the plates B. The potential difference between the plates C. The size and shape of the plates D. All of the above

C. The size and shape of the plates

In a static situation, what could a conducting object be replaced with to generate the same electric field? A. any dielectric of the same shape B. a dielectric of the same shape with a very small dielectric constant C. a dielectric of the same shape with a very large dielectric constant

C. a dielectric of the same shape with a very large dielectric constant

A 2µF parallel-plate capacitor with plate separation 2.0mm is connected to a 6V battery. What is the electric field between the plates when the system is in equilibrium? A. 1 × 10^−2 N/C B. 1 N/C C. 50 N/C D. 3000 N/C E. 6000 N/C

D. 3000 N/C

Select the statement that follows that is true about equipotential surfaces. A. Equipotentials can never cross. B. Equipotentials can only cross at right angles. C. Only equipotential lines with zero potential can cross. D. Equipotentials can only cross at points of zero electric field. E. Equipotentials can only cross at points of zero electric potential energy

D. Equipotentials can only cross at points of zero electric field.

A dielectric with dielectric constant κ is added to a field map. Before the addition of the dielectric, N field line pass through the space that will be occupied by the dielectric. Approximately how many field lines pass through the dielectric after it is placed in the field? A. 0 B. N C. κN D. N/κ E. N/2

D. N/κ

Imagine that the conductor has a hollow, empty cavity inside. You bring the conductor close to a point charge Q. Is there a field inside the cavity? Is there a charge on the inner surface (the cavity's boundary)? A. There is a field in the cavity, but no charge on the inner surface B. There is a surface charge but no field C. There is both a field and a surface charge D. There is neither a field nor a surface charge

D. There is neither a field or surface charge

Two pie pans (aluminum plates) are spaced 3cm apart and charged by a battery. The field between the plates may be approximated as that of two infinite parallel planes. A battery establishes equal and opposite charge Q on the plates which creates a potential difference of 1.5V between the plates. The plates are circular with radius 10cm. Calculate the charge Q on one plate. A. 4 × 10^−12C B. 6 × 10^−12C C. 2 × 10^−11C D. 7 × 10^−12C E. 1 × 10^−11C

E. 1 × 10^−11C

In the book, Electronic Gadgets for the Evil Genius, they describe an electronic pulser that uses capacitors with energy storage of 5000.0J. If something went wrong, and all this energy got converted into kinetic energy of a small piece of metal (say of the mass of a 45 caliber bullet m = 0.0149kg), how fast would the piece of metal be going? Note this is strictly a kinetics problem, no electricity and magnetism required. Second note, be very careful with high voltage systems. For your reference, the muzzle velocity of a rifle is about 350 m/s. A. 336, 000 m/s B. 580.0 m/s C. 1.20 m/s D. 12.4 m/s E. 819 m/s

E. 819 m/s