Physics Exam 4
An electron moving in the +y direction, at right angles to a magnetic field, experiences a magnetic force in the -x direction. The direction of the magnetic field is in the
+z direction
A 5-uf, a 7-uf, and an unknown capacitor Cx are connected in parallel between points a and b as shown in the figure. What do you know about the equivalent capacitance Cab between a and b? (There could be more than one correct choice)
- Cab > Cx - Cab > 12 uF
The figure shows conventional current passing through a resistor. The arrow shows the direction in which this conventional current is flowing. Which of the following statements are correct? (There could be more than one correct choice)
- The current at point b is the same as the current at point a - The electric potential is lower at point b than at point a
The figure shows electrons passing through a resistor. The arrow shows the direction in which the electrons are moving. Which of the following statements are correct? (There could be more than one correct choice)
- The electric potential is higher at point b than at point a - The speed of the electrons at point b is the same as it is at point a - The electrons are losing electric potential energy as they move through the resistor from a to b
When two or more different capacitors are connected in parallel across a potential source (battery), which of the following statements must be true? (There could be more than one correct choice)
- The potential difference across each capacitor is the same - The capacitor with the largest capacitance has the most charge
The maximum torque on a flat current-carrying loop occurs when the angle between the pane of the loop's area and the magnetic field vector is
0*
Which one of the following quantities is equivalent to 1 W?
1 V x A
Which one of the following quantities is equivalent to 1 Ohm
1 V/A
When current is flowing in an ordinary metal wire, the magnitude of the average velocity of the electrons is closest to
1 mm/s
For the graph shown in the figure, what physical quantity does the slope of the graph represent for a dc circuit? (Potential/Power)
1/(current)
For the graph shown in the figure, what physical quantity does the slope of the graph represent for ohmic material? (Resistance/Potential)
1/(current)
For the graph shown in the figure, what physical quantity does the slope of the graph represent for a dc circuit? (Current/Power)
1/(potential)
For the graph shown in the figure, what physical quantity does the slope of the graph represent for ohmic material? (Current/Potential)
1/(resistance)
If the length and diameter of a wire of circular cross section are both tripled, the resistance will be
1/3 of what is originally was
During a period of high power demand, the voltage output of the power company is reduced by 5.0%. By what percentage is the power in a resistor decreased?
10%
The magnetic field at a distance of 2 cm from a long straight current-carrying wire is 4 uT. What is the magnetic field at a distance of 4 cm from this wire?
2 uT
You are given a copper bar of dimensions 3 cm × 5 cm × 8 cm and asked to attach leads to it in order to make a resistor. If you want to achieve the largest possible resistance, you should attach the leads to the opposite faces that measure
3 cm x 5 cm
You are given a copper bar of dimensions 3 cm × 5 cm × 8 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
5 cm x 8 cm
The magnetic field at a distance of 2 cm from a long straight current-carrying wire is 4 uT. What is the magnetic field at a distance of 1 cm from this wire?
8 uT
Identical light bulbs can be attached to identical ideal batteries in three different ways (A, B, or C), as shown in the figure. The ranking (from lowest to highest) of the total power produced by the battery is
B, A, C
Two long parallel wires are placed side-by-side on a horizontal table and carry current in the same direction. The current in one wire is 20 A, and the current in the other wire is 5 A. If the magnetic force on the 20-A wire has a magnitude F, what is the magnitude of the magnetic force on the 5-A wire? No external magnetic fields are present.
F
In the circuit shown in the figure, the resistor R has a variable resistance. As R is decreased, what happens to the currents?
I1 decreases and I2 increases
The length of a certain wire is kept same while its radius is doubled. What is the new resistivity of this wire?
It does not change
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
The length of a certain wire is doubled and at the same time its radius is reduced by a factor of 2. What is the new resistance of this wire?
It is 8 times as large
The length of a certain wire is kept the same while its radius is doubled. What is the new resistance of this wire?
It is reduced by a factor of 4
A resistor, an uncharged capacitor, a dc voltage source, and an open switch are all connected in series. The switch is closed at time t = 0 s. Which one of the following is a correct statement about the circuit?
Once the capacitor is essentially fully charged, there is no current in the circuit
A rectangular coil, with corners labeled ABCD, has length L and width w. It is placed between the poles of a magnet, as shown in the figure. If there is a current I flowing through this coil in the direction shown, what is the direction of the force acting on section AB of this coil?
Perpendicular to and into the page
Three identical capacitors are connected in 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
Three identical capacitors are connected in parallel to a potential source (battery). If a charge of Q flows into this combination, how much charge does each capacitor carry?
Q/3
A proton, moving in a uniform magnetic field, moves in a circle perpendicular to the field lines and takes time T for each circle. If the proton's speed tripled, what would now be its time to go around each circle?
T
You obtain a 100-W light bulb and a 50-W light bulb. Instead of connecting them in the normal way, you devise a circuit that places them in series across normal household voltage. If each one is an incandescent bulb of fixed resistance, which statement about these bulbs is correct?
The 50-W bulb glows more brightly than the 100-W bulb
A resistor, an uncharged capacitor, a dc voltage source, and an open switch are all connected in series. The switch is closed at time t = 0 s. Which one of the following is a correct statement about this circuit?
The charge on the capacitor after four time constants is about 98% of the maximum value
Four unequal resistors are connected in a parallel with each other. Which one of the following statements is correct about this combination?
The equivalent resistance is less than that of the smallest resistor
Four unequal resistors are connected in series with each other. Which one of the following statements is correct about this combination?
The equivalent resistance is more than the largest resistance
A rectangular coil, with corners labeled ABCD, has length L and width w. It is placed between the poles of a magnet, as shown in the figure. If there is current I flowing through this coil in the direction shown, what is the direction of the force acting on section BC of this coil?
The force is zero
A wire lying in the plane of this page carries a current directly toward the top of the page. What is the direction of the magnetic force this current produces on an electron that is moving perpendicular to the page and outward from it on the left side of the wire?
The force is zero
A long straight wire has a constant current flowing to the right. A rectangular metal loop is situated above the wire, and also has a constant current flowing through it, as shown in the figure. Which one of the following statements is true?
The net magnetic force on the rectangle is downward, and the net torque on it is zero
Which one of the following statements is correct?
The north pole of a magnet points towards Earth's geographic north pole.
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
If a calculated quantity has a units of N * s / C * m , that quantity could be
a magnetic field
A charged particle moving along the +x axis enters a uniform magnetic field pointing along the +z-axis. A uniform electric field is also present. Due to the combined effect of both fields, the particle does not change its velocity. What is the direction of the electric field?
along the +y-axis
A wire of resistivity p must be replaced in a circuit by a wire of the same material but four times as long. If, however, the total resistance is to remain as before, the diameter of the new wire must
be two times the original diameter
Consider an ideal solenoid of length L, N windings, and radius b (L is much longer than b). A current I is flowing through the wire windings. If the length of the solenoid becomes twice as long (to 2L), but all the other quantities remain the same, the magnetic field inside the solenoid will
become one-half as strong as initially
When a current flows through an ionic liquid such as salty water, the moving charges are
both positive and negative ions
A negatively-charged particle moves across a constant uniform magnetic field that is perpendicular to the velocity of the particle. The magnetic force on this particle
causes the particle to accelerate
If a quantity you calculated has units of A ∙ s, what is that quantity?
charge
A horizontal wire carries a current straight toward you. From your point of view, the magnetic field caused by this current
circles the wire in a counter-clockwise direction
A single current-carrying circular loop of radius R is placed next to a long, straight wire, as shown in the figure. The current I in the wire flows to the right. In which direction must current flow in the loop to produce a net magnetic field of zero at its center?
clockwise
A straight bar magnet is initially 4 cm long, with the north pole on the right and the south pole on the left. If you cut the magnet in half, the right half will
contain a north pole on the right and a south pole on the left
A long, straight wire carrying a current is placed along the y-axis. If the direction of the current is in the +y direction, what is the direction of the magnetic field due to this wire as you view it in such a way that the current is coming directly toward you?
counterclockwise, around the y-axis
For the graph shown in the figure, what physical quantity does the slope of the graph represent for a dc circuit? (Power/Potential)
current
If the resistance in a constant voltage circuit is doubled, the power dissipated by that circuit will
decrease to one-half its original value
A wire lying in the plane of the page carries a current toward the bottom of the page, as shown in the figure. What is the direction of the magnetic force it produces on an electron that is moving to the left directly toward the wire, as shown?
directly toward the bottom of the page
When you double the number of windings in an ideal solenoid while keeping all other parameters (radius, length, and current) fixed, the magnetic field at the center of the solenoid will
double
For the horseshoe magnet shown in the figure, the left end is a north magnetic pole and the right end is a south magnetic pole. When the switch is closed in the circuit, which way will the wire between the poles of the horseshoe magnet initially deflect?
downward
A charged particle is injected into a uniform magnetic field such that its velocity vector is perpendicular to the magnetic field lines. Ignoring the particle's weight, the particle will
follow a circular path
A wire is carrying a current vertically downward. What is the direction of the force on this wire due to Earth's magnetic field?
horizontally towards the east
A charged particle moves with a constant speed through a region where a uniform magnetic field is present. If the magnetic field points straight upward, the magnetic force acting on this particle will be strongest when the particle moves
in a plane parallel to Earth's surface
Suppose you have two capacitors and want to use them to store the maximum amount of energy by connecting them across a voltage source. You should connect them
in parallel across the source
When the current through a resistor is increased by a factor of 4, the power dissipated by the resistor
increases by a factor of 16
When a ferromagnetic material is placed in an external magnetic field, the net magnetic field of its magnetic domains becomes
larger
A charged particle that is moving in a static uniform magnetic field
may experience a magnetic force, but its speed will not change
When a current flows through a metal wire, the moving charges are
only electrons
A long straight wire carrying 4-A current is placed along the x-axis as shown in the figure. What is the direction of the magnetic field at point P due to this wire?
out of the plane of the page
An electron is moving to the right, as shown in the figure. Suddenly if it encounters uniform magnetic field pointing out of the page. Which one of the three paths shown will it follow in the field?
path a
A rectangular coil, with corners labeled ABCD, has length L and width w. It is placed between the poles of a magnet, as shown in the figure. If there is current I flowing through this coil in the direction shown, what is the direction of the force acting on section CD of this coil?
perpendicular and out of the page
The direction of the force on a current-carrying wire in a magnetic field is
perpendicular to both the current and the magnetic field
A current-carrying loop of wire lies flat on a horizontal tabletop. When viewed from above, the current moves around the loop in a counterclockwise sense. For points on the tabletop inside the loop, the magnetic field lines caused by this current
point straight up
Two long parallel wires placed side-by-side on a horizontal table carry identical size currents in opposite directions. The wire on your right carries current directly toward you, and the wire on your left carries current directly away from you. From your point of view, the magnetic field at a point exactly midway between the two wires
points downward
For the graph shown in the figure, what physical quantity does the slope of the graph represent for a dc circuit? (Power/Current)
potential
If a quantity you calculated has units of (Ohm)(m), what is that quantity?
potential
If a quantity you calculated has units of (kg)(m^2)/(s^2)(C), what is that quantity?
potential
If the current flowing through a circuit of constant resistance is doubled, the power dissipated by that circuit will
quadruple in magnitude
Consider an ideal solenoid of length L, N windings, and radius b (L is much longer than b). A current I is flowing through the wire windings. If the radius of the solenoid is doubled to 2b, but all the other quantities remain the same, the magnetic field inside the solenoid will
remain the same
For the graph shown in the figure, what physical quantity does the slope of the graph represent for ohmic material? (Potential/Current)
resistance
If a quantity you calculated has units of (kg)(m^2)/(s)(C^2) what is that quantity?
resistance
A 9-V battery is hooked up to two resistors in series. One has a resistance of 5 Ohm, and the other has a resistance of 10 Ohm. Several locations along the circuit are marked with letters, as shown in the figure. Through which resistor is energy being dissipated at the higher rate?
the 10-ohm resistor
When unequal resistors are connected in series across an ideal battery,
the current flowing in each is the same
Kirchhoff's junction rule is a statement of
the law of conservation of charge
A charged particle moving along the +x-axis enters a uniform magnetic field pointing along the +z-axis. Because of an electric field along the +y-axis, the charged particle does not change velocity. What is the sign of the particle?
the particle could be either positive or negative
When unequal resistors are connected in parallel in a circuit,
the potential drop is always the same across each resistor
The figure shows a graph of the resistance of a wire as a function of its length. What physical quantities does the slope of this graph represent? (Resistance/Length)
the resistivity of the material divided by the cross-sectional area of the wire
A flat circular wire loop lies in a horizontal plane on a table and carries current in a counterclockwise direction when viewed from above. At this point, the earth's magnetic field points to the north and dips below the horizontal. Which side of the coil tends to lift off of the table due to the magnetic torque on the loop?
the south side
Two long parallel wires are placed side by side on a horizontal table. If the wires carry current in the same direction,
the wires pull toward each other.
Two long parallel wires are placed side-by-side on a horizontal table. If the wires carry current in opposite directions,
the wires push away from each other
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 with the first one, the time constant of the new RC circuit will be
three times as large as before
An electron has an initial velocity to the south but is observed to curve upward as the result of a magnetic field. This magnetic field must have a component
to the west
A long, straight, horizontal wire carries current toward the east. A proton moves toward the east alongside and just south of the wire. What is the direction of the magnetic force on the proton?
toward the north
A long, straight, horizontal wire carries current toward the east. An electron moves toward the east alongside and just south of the wire. What is the direction of the magnetic force on the electron?
toward the south
At a particular instant, an electron moves toward the east in a uniform magnetic field that is directed straight downward. The magnetic force that acts on it is
toward the south
A vertical wire carries a current straight up in a region where the magnetic field vector points toward the north. What is the direction of the magnetic force on this wire?
toward the west
A proton, moving north, enters a magnetic field. Because of this field, the proton curves downward. We may conclude that the magnetic field must have a component
towards the east
An electron, moving west, enters a magnetic field. Because of this field the electron curves upward. We may conclude that the magnetic field must have a component
towards the north
A proton, moving west, enters a magnetic field. Because of this magnetic field the proton curves upward. We may conclude that the magnetic field must have a component
towards the south
An electron, moving south, enters a magnetic field. Because of this, the electron curves upward. We may conclude that the magnetic field must have a component
towards the west
If a calculated quantity has units of T * m/A that quantity could be
u0
A ring with a clockwise current (as viewed from above the ring) is situated with its center directly above another ring, which has a counter-clockwise current, as shown in the figure. In what direction is the net magnetic force exerted on the top ring due to the bottom ring?
upward
A proton is to orbit Earth at the equator using Earth's magnetic field to supply part of the necessary centripetal force. In what direction should the proton move?
westward