damn
With the switch in the circuit of the top figure closed, there is no current in R2 because the current has an alternate zero-resistance path through the switch. There is current in R1, and this current is measured with the ammeter (a device for measuring current) at the bottom of the circuit. If the switch is opened (the bottom figure), there is current in R2. What happens to the reading on the ammeter when the switch is opened?
(b) The reading goes down.
A square, flat loop of wire is pulled at a constant velocity through a region of uniform magnetic field directed perpendicular to the plane of the loop (see below). Which statements are correct?
(c) No current is induced(d) Charge separation occurs in the loop with the top one being positive
Consider a proton and electron that are 0.05 nm apart and at rest. (This is roughly the separation of these particles in a hydrogen atom). Calculate the force that their electromagnetic interaction exerts on each particle along the axis connecting them. Consider whether these forces repel or attract.
-9.2x10^-8 N
At which phase angle is an RLC series circuit at resonance?
0 degrees
Consider the familiar equipotential diagram below. In the expression |E→p|=b|E→Q|, what is the approximate value of b? (Approximate because you're not given the exact distances between equipotentials).
1/2
There's a ring of radius R. A total of Q of charge is distributed uniformly on that ring. What is the potential at the center of the ring?
1/4pie * Q/R
Two wires have basically equal electron number densities. Assume that (1) the electric field in each wire points directly along the wire,(2) The electric fields in the two wires have the same magnitude, (3) Conductivity in wire A is twice that of wire B. This means that the drift belocity in wire A is f times that in wire B. What is f?
2
A circular loop of wire is falling toward a current carrying wire (conventional current flowing to the left). What is the direction of the induced current in the loop of wire?
2. Counterclockwise
A series RLC circuit constains a 20Ωresistor, a 0.75 uF capacitor, and a 120 mH inductor. We apply a sinusoidally varying rms voltage of 120 V across this circuit a frequency of 500 Hz. What is the rms current in the circuit ? (you cannot do this in your head...probably).
2.33 A
In the LR circuit below, take the resistor to be 10 Ohms, and the coil to have an inductance of 10 mH. About how long will it take for the current to fall to 0.05 times its initial value? (Hint: 0.05 is approximately (1/e)3, so you should be able to do this in your head. Actually, I KNOW you can!)
3 ms
A series RLC circuit constains a 20Ωresistor, a 0.75 uF capacitor, and a 120 mH inductor. We apply a sinusoidally varying rms voltage of 120 V across this circuit. What is the rms current in the circuit when operating at the resonant frequency? (you can do this in your head).
6.00 A
A capacitor with two square plates 1 m on a side has a capacitance of 1 F. Well, the numbers sure are convenient. What is the separation between the plates?
8.85e-12
If we increase the resistance in this LR circuit, how would this change the rate of decay of the current through the coil?
A. Current will decay more quickly
Consider the two inductors below (they're in separate, independent circuits). The induced EMF in each inductor is such that the inductor behaves like a battery with its positive end to the right. In which is the current changing more rapidly?
A. Inductor 1
Two coils are placed near each other as shown in the figure. The coil on the left is connected to a battery and a switch and thecoil on the right is connected to a resistor.What is the direction of the field induced through the coils on the right hand side?
A. Left
A current may be induced in a coil by:
A. Moving one end of a bar magnet through the coilB. Moving the coil toward one end of the bar magnetC. Holding the coil near a second coil while the electric current in the second coil is increasing
Suppose we have a certain length of wire that we would like to wind around a cylindrical form in a single layer of closely spaced turns to make it more compact and we would like to minimize the inductance of the resulting coil. All the forms are small enough in radius so that 𝑙 >𝑟, meaning we can use our ideal solenoid equations.
A. The smallest radius
The centers of two circular loops are separated by a fixed distance. For what relative orientation of the loops is their mutualinductance at maximum?
A. coaxial and lying in parallel planes
he graphs below show plots of ϕ(x,y,z)vs xfor fixed y,zin various electric fields. In which case is the magnitude of Exlargest at x=2cm?
B
Coil 1 is moved closer to coil 2 with the orientation of both coils remaining fixed. Because of this movement, the mutual induction of the two coils
B. Increases
Two rectangular loops of wire lie in the same plane as shown in the figure. If the current I in the outer loop is counterclockwise and increases with time, what is true of the current induced in the inner loop? Choose all that are correct
B. It is clockwise. D. Its magnitude depends on the dimensions of the loops.
A solenoidal inductor for a printed circuit board is being redesigned. To save weight, the number of turns is reduced by one-half, with the geometric dimensions kept the same. By how much must the current change if the energy stored in the inductor is to remain the same?
B. It must be two times larger.
Two coils are placed near each other as shown in the figure. The coil on the left is connected to a battery and a switch and thecoil on the right is connected to a resistor.What is the direction of the current in the resistor at an instant immediately afterthe switch is thrown closed?
B. Right
The bar in the figure moves on rails to the right with a velocity v, and a uniform, constant magnetic field is directed out of the page. Choose all statements that are correct
B. The induced current in the loop is clockwise. D. An external force is required to keep the bar moving at constant speed.
Two bulbs are shown in a circuit that surrounds a region of increasing magnetic field directed out of the page. When the switch is closed,
C. Both bulbs glow equally brightly
In an LC circuit, if we increase the initial charge on the capacitor (without changing anything else), the circuits oscillation frequency will:
C. Remain the same
A flat coil of wire is placed in a uniform magnetic field that is in the y direction. The magnetic flux through the coil is maximized if the plane of the coil is in: (choose all that are correct)
C. The xzplane
The loop of wire is being moved to the right at constant velocity. A constant current I flows in the long straight wire in the direction shown. The current induced in the loop is
C. Zero
Two particles whose charges have equal magnitude (q), but opposite signs are placed as shown below. Potential is zero at infinity. At which point is potential largest?
D
Two solenoids, A and B, are wound using equal lengths of the same kind of wire. The length of the axis of each solenoid is large compared with its diameter. The axial length of A is twice as large as that of B, and A has twice as many turns as B. What is the ratio of the inductance of solenoid A to that of solenoid B?
D. 1/2
Two bulbs are shown in a circuit that surrounds a region of increasing magnetic field directed out of the page. When the switch is closed, (dots on right)
D. Bulb 1 goes out
Initially, an inductor with no resistance carries a constant current. Then the current is brought to a new constant value twice as large. Afterthis change, when the current is constant at its higher value, what has happened to the emf in the inductor?
D. It continues to be zero.
In an LC circuit, if we increase the capacitor's capacitance (but not change anything else), the circuit's oscillation frequency will:
Decrease
Assume that the electric potential field in a certain region is ϕ(x,y,z)=ay, where ais a constant. Computer the electric field vector E→ in this region. (a) 0 (b) 12ay2in the y direction (c) ayin the -y direction (d) the field is a constant a N/C in the y direction (e) the field is a constant a N/C in the -y direction
E
Consider our familiar circuit of a battery and a lightbulb, connected by some wire (which is the same material as the lightbulb filament).The numbers label various points inside the wires. Which graph best describes the electrostatic potential, ϕ?
E
Determine the magnitude and direction of the electric field vector E at point P in the situation shown below (assume that each ball is actually a point particle). Where k=14πε
E = kq (4- sqrt2) / d^2
Two bulbs are shown in a circuit that surrounds a region of increasing magnetic field directed out of the page. When the switch is open,
E. Both bulbs are dark
Object A has a charge of +2uC, and object B has a charge of +6uC. Which statement is true?
Fab = -Fab
magine that we suspend two small plastic spheres with a mass m using insulating threads of length L from a common point. If the spheres are uncharged they will hang so they touch; but when they are both given the same charge q, they repel each other and hang a distance d apart, as shown below. Assume that d is pretty small compared to L but large compared to the diameter of the balls. Find the magnitude of the force each ball feels in terms of g (gravity).
Fe = mgtan(0)
Wire A has a diameter half that of wire B, but is otherwise the same. The electric field acting inside each wire has the same magnitude. How do the currents flowing through these two wires compare?
IA= 1/4IB
Three charged particles are arranged on corners of a square as shown, with charge -Q on both the particle at the upper left corner and the particle at the lower right corner and with charge +2Q on the particle at the lower left corner. Suppose the +2Q charge at the lower left corner is removed. Then the magnitude of the field at the upper right corner:
Increases
At an instant of time during the oscillations of an LC circuit, the current is at its maximum value. At this instant, what can be said about the voltage across the capacitor?
It has a maximum value
A suspended object A is attracted to a neutral wall. It's also attracted to a positively charged object B. Which of the following is true about object A?
It has a negative charge
A bar magnet is held in a vertical orientation above a loop of wire that lies in the horizontal plane (see below). The sound end of the magnet is aimed at the loop. After the magnet is dropped, what is true of the induced current in the loop as viewed from aove?
It is clockwise as the magnet falls towards the loop
Which configuration corresponds to the highest potential energy?
Q r 2Q
magine that we suspend two small plastic spheres with a mass m using insulating threads of length L from a common point. If the spheres are uncharged they will hang so they touch; but when they are both given the same charge q, they repel each other and hang a distance d apart, as shown below. Assume that d is pretty small compared to L but large compared to the diameter of the balls. Find the magnitude of the force each ball feels in terms of g (gravity).
Radial
Consider the equipotential diagram below. The lines are spaced equally. Where is the electric field highest?
Same non-zero magnitude at point P and point Q
Two lightbulbs both operate on 120V. One has a power of 25 W and the other 100 W. Which lighbulb carries more current?
The bright 100 W
A "free" electron and a "free" proton are placed in an identical electric field. Which of the following statements are true? (choose all that are correct)
The electric force on the proton is equal in magnitude to the electric force on the electron, but in the opposite direction The magnitude of the acceleration of the electron is greater than of the proton
A resistor, a capacitor and an inductor walk into a bar. No, wait, they're connected in series and across an AC power source. Which statement is FALSE (only one):
The sum of the rms voltages across the three elements is the same as the rms voltage across the combination (i.e. of the source).
A piece of aluminum is dropped vertically downward between the poles of an electromagnet. Does the magnetic field affect the velocity of the aluminum?
True
If the electric field at any point inside a conductor is nonzero, then the metal is not in static equilibrium.
True
In static equilibrium, any excess charge on a conductor is uniformly spread on the surface.
True
This is the same picture as for the question in class, but the situation is a bit different. Two coils are placed near each other. The left one is connected to a battery and a switch and the one on the right is connected to a resistor. What is the direction of the current in the resistor after the switch has been closed for several seconds ?
Zero
Consider positive and negative charges moving horizontally through the four regions shown below. Rank the current in these four regions from highest to lowest.
a, b=c, d
Rank the magnitudes of the electric field at points A, B, and C in the figure below, with the largest magnitude first (do not assign any special meaning to number of lines emanating from each charge, I just didn't make a symmetric drawing, but imagine it's exactly same on both sides).
a. b. c
Direction of force of 2u
b) upper left
Consider a simple capacitor made of a pair of conducting plates in close proximity. Suppose the plates are appropriately charged with +q and -q and then discharged to produce a spark. Next, you charge them again, exactly the same. But, now, you pull them farther apart. They're discharged (shorted) a second time. Will the spark produced be:
bigger (liberate more energy) than the first spark
Which configuration corresponds to the lowest potential energy?
c) Q 2r -Q
A loop of wire is moving near a long straight wire carrying a constant current I as shown below. What is the direction of the induced current in the loop as it moves away from the wire.
counterclockwise
Three charged particles are arranged on corners of a square as shown in the figure, with charge -Q on both the particle at the upper left corner and the particle at the lower right corner and with charge +2Q on the particle at the lower left corner. What is the direction of the electric field at the upper right corner, which is a point in empty space?
d
Consider the equipotential diagram below. If you place a proton at point P, which way will it move? (use directions in the diagram on the right)
down
What happens to the magnitude of the charge on each plate of a parallel plate capacitor if the potential difference between the conductors is doubled?
factor of 2
If each copper atom in a wire were to contribute TWO conduction electrons instead of just one, its conductivity would:
increase by a factor of 2
The average power input to a series AC circuit is minimum when:
only a capacitor is present in the circuit
Consider circuit below. We start with S1 (switch) open and S2 at position (a), as shown. We then close switch S1 and wait a long time. Across which element is the voltage the same as the EMF of the battery?
resistor
You have a piece of metal and at some point in the metal, the drift velocities of electrons are oriented leftward. What is the direction of the conventional current in this metal is:
rightward
Consider circuit below. We start with S1 (switch) open and S2 at position (a), as shown. At the instant that we close S1, across which element is the voltage the same as the EMF of the battery?
the inductor
For a thin, uniform metal wire in a circuit that is in dynamic equilibrium, the current flow in the wire is constant in time.
true
For a thin, uniform metal wire in a circuit that is in dynamic equilibrium, the current is the same for any cross-sectional area spanning the wire at any point along the wire.
true
The electric dipole will polarize the neutral atom.
true
