E&M Physics 231 Final

Two parallel sheets a distance d apart have their centers directly opposite each other. The sheets carry equal but opposite uniform surface charge densities. A point charge that is placed near the middle of the sheets a distance d/2 from each of them feels an electrical force F due to the sheets. If this charge is now moved closer to one of the sheets so that it it a distance d/4 from the sheet what will the force feel?

F

A negatively charged rod is brought close to (not touching) 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.

Two point charges of +20 muC and -8 muC are separated by a distance of 20 cm. What is the magnitude of electric field due to these charges at a point midway between them.

25.2×10^6 N/C directed toward the negative charge.

An uncharged conductor has a hollow cavity inside of it. Within this cavity, there is a charge of +10 muC that does not touch the conductor. There are no other charges in the vicinity. Which statement about this conductor is true.

The outer surface has +10 muC and the inner contains -10muC

A charge 1=2 muC is placed at the origin in a region where there is already a uniform electric field E = 100 N/C i. Calculate the flux of the net electric field through a gausssian sphere of radius R= 10Cm centered at the origin.

2.26×10^5 N*m²/s

A conducting sphere of radius R carries an excess positice charge and is very far from any other charges. Which one of the following graphs best illustrates the potential produced by this sphere as a function of the distance r from the center of the sphere.

The graph starts at a place above the x axis and remains constant until R, where it decreases parabolically downward.

In a certain region the electric potential due to a charge distribution is given by the equation V(x,y) = 2xy - x² - y, where x and y are measured in meters and v is in volts. At which point is the electric field equal to zero.

x = 0.5m, y=0.5m

If the elctric potential in a region is given by V(x) = 6/x², the x component of the electric field in that region is.

12x^-3

When two or more capacitors are connected in parallel across a potential difference,

The potential difference across each capacitor is the same

Five capacitors are connected across a potential difference Vab as shown in the figure. Because of the dielectrics used each capacitor will break down if the potential across it exceeds 30 V the largest that Vab can be without damaging the capacitors is closest to?

Find the charge and use the smallest capacitance capacitor to check.

A 6 muF parallel plate capacitor has charges of +-40muC on its plates. How much potential energy is stored in this capacitor?

133muJ

How much energy (in milliJ) is stored in a 86 MicroFarad capacitor if the voltage across the capacitor is 34 V

49.71

Two 2.8 MicroCoulomb charges are 3.6 m apart. How much energy (in milliJoule) went into assembling these two charges?

19.6

A 44 MicroCoulomb charge is located at the origin and a -16 microCoulomb charge is located on the y-axis at y = 48.6cm. what is the magnitude of the force with which the charges attract each other in units of N?

26.83

The figure shows a steady electric current passing through a wire with a narrow region. What happens to the drift velocity of the moving charges as they go from wide region(A) to narrow region (B) to wide region (C)

The drift velocity increases from A to B and decreases from B to C.

A wire of resistivity rho must be replaced in a circuit by a wire of the same material but 4 times as long. If, however, the resistance of the new wire is to be the same as the resistance of the original wire, the diameter of the new wire must be

2 times the diameter of the original wire.

If a current of 2.4 A is flowing in a cylindrical wire of diameter 2.0 mm what is the average current density in this wire?

7.6×10^5 A/m²

In the circuit shown, four identical resistors labeled A to D are connected to a battery as shown. S1 and S2 are switches. Which of the following actions would result in the GREATEST amount of current through the resistor A?

Closing both switches

In the circuit shown in the figure the lightbulbs are all identical. Which of the following is the correct ranking of the brightness of the bulbs. A is in parallel with B and C which are in series.

A is the brightest, and B and C have equal brightness but less than A.

An electron moving in the direction of the + x axis enters a magnetic field. If the electron experiences a magnetic deflection in the -y direction the magnetic field in this region points in the direction of the

-z-axis

A vertical wire carries a current vertically upward in a region where the magnetic field vector points toward the north. what is the direction of the magnetic force on this current due to the field?

West

A straight wire that is 0.6 m long is carrying a current of 2 A it is placed in a uniform magnetic field of strength 0.3 T. If the wire experiences a force of 0.18 N what angle does the wire make with respect to the magnetic field.

30

An electron moving perpendicular to a uniform magnetic field of 3.2 × 10^-2 T moves in a circle of radius 0.4cm. How fast is this electron moving? (mel = 9.11×10^-31 kg, e=1.6×10^-19 C)

2.2×10^7

A very long hollow thin-walled conducting cylindrical shell (pipe) of radius R carries a current along its length uniformly distributed throughout the thin shell. Which one of the graphs shown in the figure most accurately describes the magnitude B of the magnetic field produced by this current as a function of the distance r from the central axis.

The correct graph is zero until R, where there is a jump discontinuity upwards, after which the function decreases exponentially.

A current of 4.1 A flows through the heating element of heater converting 791 J of electrical energy into thermal energy every second. What is the voltage (in V) across the ends of the heating element.

192.9

A wire carries a steady current of 1.9 A. A straight section of the wire is 0.98m long and lies along the y-axis within a uniform field B = 1.22 T in the z-direction. What is the magnitude of the force on the section of wire in N.

2.27

Find the current I (in A) in a long straight wire that would produce a magnetic field of 3.9×10^-4 Tat a distance of 3.43 cm from the wire.

66.9