Physics 2 Exam 2 conceptuals

The same amount of current III is flowing through two wires, labeled 1 and 2 in the figure, in the directions indicated by the arrows. In this problem you will determine the direction of the net magnetic field B⃗ netB→netB_net_vec at each of the indicated points (A - C) What is the direction of the magnetic field B⃗ netB→netB_net_vec at point A? Recall that the currents in the two wires have equal magnitudes. What is the direction of the magnetic field B⃗ netB→netB_net_vec at point B? What is the direction of the magnetic field B⃗ netB→netB_net_vec at point C?

B⃗ netB→netB_net_vec points out of the screen at A. ⃗B net=0B→net=0 at B. B⃗ netB→netB_net_vec points into the screen at C.

Which of the following laws or relationships would be most appropriate for calculating the magnetic field at the center of a rectangular loop of wire?

B) Biot-Savart

Two very long wires carry equal currents in the same direction as shown. The electromagnetic force on the right-hand wire (#2):

B) is to the left.

The same current flows through each of the wires sketched below. For which case is the magnetic field at point O the largest? (All segments are circular or straight and the drawings are to scale. When wires point off along straight lines, they continue to infinite distance.)

C.) pictrue that adds together

A coil lies flat on a tabletop in a region where the magnetic field vector points straight up. The magnetic field vanishes suddenly. When viewed from above, what is the direction of the induced current in this coil as the field fades?

CCW

The same current flows through each of the wires sketched at right. For which case is the magnetic field at point O the largest? (All segments are circular or straight. Radii are d or d/2. When wires point off along straight lines, they continue to infinite distance.)

Case 1.

The magnetic field at the center of a circular coil of wire with N0 turns and radius R0 and carrying current I0 can be doubled by:

) reducing the radius to R0/2

The bent wire circuit shown in the figure (Figure 1) is in a region of space with a uniform magnetic field in the +z direction. Current flows through the circuit in the direction indicated. Note that segments 2 and 5 are oriented parallel to the z axis; the other pieces are parallel to either the x or y axis. Determine the direction of the magnetic force along segment 1, which carries current in the -x direction. Determine the direction of the magnetic force along segment 2, which carries current in the -z direction. Determine the direction of the magnetic force along segment 3, which carries current in the +y direction. Determine the direction of the magnetic force along segment 4, which carries current in the +x direction. Determine the direction of the magnetic force along segment 5, which carries current in the +z direction. Determine the direction of the magnetic force along segment 6, which carries current in the +x direction. Determine the direction of the magnetic force along segment 7, which carries current in the -y direction.

+y 0 +x -y 0 -y -x

At the instant shown, the direction of the magnetic field vector at point 𝑃1 is

+z

The direction of the magnetic field at the point 𝑃 (2.00 m, 0.00 m, 0.00 m) is

-z

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 direction of the magnetic field in this region points in the direction of the

-z-axis Use RHR: thumb towards you , pointer left and middle down. or thumb -y and wrap down. iX-j=-k

Three particles travel through a region of space where the magnetic field is out of the page, as shown in the figure. Only magnetic forces act on the particles. The arrows denote the trajectories of the particles. The electric charge of each of the three particles is, respectively,

1 is negative, 2 is neutral, and 3 is positive.

A very long, solid, conducting cylinder of radius R carries a current along its length uniformly distributed throughout the cylinder. 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?

1.) liner line up to R then concave back down to zero

Use the information given here to answer questions 10-12. The magnetic field in an electromagnetic wave is given by B=B0sin(10z+ct)i . The intensity of this wave is I0. 10) The electric field in this wave is best represented by: 11) If the magnetic field amplitude B0 in this electromagnetic wave is doubled, the intensity becomes: 12) The direction of propagation of this wave is:

10. E=E0sin(10z+ct)j 11. 4 I0 12. in the -z direction

Questions 11, 12, and 13 deal with the situation displayed in the figure at right: a rectangular wire loop of width 𝑤 = 0.10 m, length 𝑙 = 0.20 m, and resistance 𝑅 = 5.0 Ω is moving upward at constant velocity 𝒗⃗ out of a region of constant magnetic field (shaded area) with magnitude 𝐵 = 0.40 T. At the time shown in the figure, the loop is half-way out of the magnetic field region, and there is an induced clockwise current 𝐼ind = 0.038 A running through the wire.

12.)into the page.

A square wire loop of side a lies in the x-y plane, in a region of magnetic field 𝑩⃗⃗ = 𝐵𝒛̂. The field strength 𝐵 changes over time, as shown in the graph to the right. The magnitude of the emf induced in the loop is greatest for the time interval

2 s to 4 s.

A resistor R0 and capacitor C0 are wired as shown. The capacitor is charged to Q0 and then the switch is moved to position b at time = zero, the charge on the capacitor decays with exponential time constant t0. If the resistance is doubled to 2R0, the charge will decay with time constant:

2t0

Two very long parallel wires in the xy-plane, a distance 2aaa apart, are parallel to the y-axis and carry equal currents III as shown in the figure. The +z direction points perpendicular to the xy-plane in a right-handed coordinate system. If both currents flow in the +y direction, which one of the graphs shown in the figure below best represents the z component of the net magnetic field, in the xy-plane, as a function of x? (Caution: These graphs are not magnetic field lines.)

3.) tangent lookin graph

In an oscillating LC circuit, the total stored energy is U and the maximum charge on the capacitor is Q. When the charge on the capacitor is Q/2, the energy stored in the inductor is closest to:

3U/4

An energy of U0 is stored in an inductor when the current flowing through it is I0. If the current is doubled to 2I0, the energy stored is closest to:

4 U0

A very long, hollow, thin-walled conducting cylindrical shell (like a 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?

4.) 0 B for R and downward slope after R

The graphs below show the current I and emf EL within an inductor as a function of time. The inductance L of the inductor is

5.0 mH.

A current of I1 is carried into the paper by the wire labeled with the X to the right. A current of I2 is carried out of the paper by the wire labeled with the dot. The magnitude of the integral ∮𝐵⃗ • 𝑑𝑠 for the dashed line path shown is:

A) Mu * absolute value I1-I2

Ampère's law is often written ∮B→(r→)⋅dl→=μ0*Iencl. A.) The integral on the left is B.) What physical property does the symbol IenclIenclI_encl represent? C.) The circle on the integral means that B→(r→) must be integrated D.) Which of the following choices of path allow you to use Ampère's law to analytically find B→(r→)? E.) Ampère's law can be used to analytically find the magnetic field around a straight current-carrying wire. F.) Ampère's law can be used to analytically find the magnetic field at the center of a square loop carrying a constant current. G.) Ampère's law can be used to analytically find the magnetic field at the center of a circle formed by a current-carrying conductor. H.) Ampère's law can be used to analytically find the magnetic field inside a toroid. (A toroid is a doughnut shape wound uniformly with many turns of wire.)

A.) the line integral along the closed loop. B.) The net current through the loop C.) along any closed path that you choose. D.) The path must pass through the point r→r_vec. And The path must have enough symmetry so that B→(r→)⋅dl→ is constant along large parts of it. E.) true F.) false G.) false H.) true

Which of the following statements is true about the inductor in the figure in the problem introduction, where I(t) is the current through the wire? Now consider the effect that applying an additional voltage to the inductor will have on the current I(t) already flowing through it (imagine that the voltage is applied to end A, while end B is grounded). Which one of the following statements is true?

If dI(t)/dt is positive, the voltage at end A will necessarily be greater than that at end B If V is positive, then I(t) could be positive or negative while dI(t)/dt will necessarily be positive.

A coil of wire having N turns, each of cross-sectional area A, is initially in a magnetic field of strength B, with the axis of the coil parallel to the magnetic field lines. The coil is then rapidly pulled from the magnetic field region and brought to a region where there is no magnetic field. What is the magnitude of ∫ 𝐸𝑀𝐹(𝑡)𝑑𝑡 from start to finish for this procedure, where EMF is the electromotive force induced in the coil when it is pulled from the field?

NBA

Ions having equal charges but masses of M and 2M are accelerated through the same potential difference and then enter a uniform magnetic field perpendicular to their path. If the heavier ions follow a circular arc of radius R, what is the radius of the arc followed by the lighter?

R/Sqrt(2) so, r=mv/qb, v=velocity 1/2mv^2=eV V=potential v= sqrt(2eV/m) R=(Sqrt(2m2eV))/qb R1=(Sqrt(m2eV))/qb divide equation this by R equation

Ions having equal charges but masses of M and 2M are accelerated through the same potential difference and then enter a uniform magnetic field perpendicular to their path. If the heavier ions follow a circular arc of radius R, what is the radius of the arc followed by the lighter?

R/sqrt(2)

A square loop of wire is pulled to the right out of a region where the magnetic field points into the paper as shown. The direction of the current in the section of wire at the top of the square is:

Right.

A capacitor is charging in a simple RC circuit with a dc battery. Which one of the following statements about this capacitor is accurate?

There is a magnetic field between the capacitor plates, even though no charge travels between them, because the electric flux between the plates is changing.

A circular metal ring is situated above a long straight wire, as shown in the figure. The straight wire has a current flowing to the right, and the current is increasing in time at a constant rate. Which statement is true?

There is an induced current in the metal ring, flowing in a clockwise direction.

As shown in the figure, two separate coiled circuits are wrapped around a cylinder. If the coiled circuit with the battery moves to the right, in which direction does the current through the resistor of the other circuit flow?

To the right.

A resistor and an ideal capacitor are connected in series to an ideal battery having a constant terminal voltage V0. At the moment contact is made with the battery, the voltages across the resistor (VR) and capacitor (VC) are closest to:

VR= V0 and VC=0.

A resistor and an ideal inductor are connected in series to an ideal battery having a constant terminal voltage V0. At the moment contact is made with the battery, the voltages across the resistor (VR) and inductor (VL) are closest to:

VR=0 and VL=V0

An electron moves in a circular trajectory of radius R0 in a uniform magnetic field of strength B0. What is the new trajectory if the field strength is doubled?

a circle of radius R0/2

A current carrying loop of wire lies flat on a table top. When viewed from above, the current moves around the loop in a counterclockwise sense. (a) For points OUTSIDE the loop, the magnetic field caused by this current (b) For points INSIDE the loop, the magnetic field caused by this current

a. points straight down. b. points straight up.

A resistor and an ideal inductor are connected in series to an ideal battery having a constant terminal voltage V 0. (a) At the moment contact is made with the battery, the voltage across the resistor is b) At the moment contact is made with the battery, the voltage across the inductor is

a. zero. b. V 0.

In the Ampere-Maxwell relation, integral w circle B Ds , the circle in integral refers to:

an integration around a closed path.

The magnetic field due to a charge at the point (0,0,0) and moving along the z axis, is greatest for which of the following positions?

at the point (0,1,0) (on the y-axis).

A charged particle accelerated to a velocity v enters the chamber of a mass spectrometer. The particle's velocity is perpendicular to the direction of the uniform magnetic field B in the chamber. After the particle enters the magnetic field, its path is a

circle.

A circular loop of wire lies in the plane of the paper. An increasing magnetic field points out of the paper. What is the direction of the induced current in the loop?

clockwise.

A capacitor C and inductor L are wired as shown to the right. The capacitor is charged with Q0. When the switch is closed, the current in the circuit oscillates with frequency f0 and amplitude I0. If the current is doubled new oscillation frequency is closest to:

f0

A large magnetic flux change through a coil must induce a greater emf in the coil than a small flux change.

false

The figure at right shows a magnet moving toward a wire loop that lies in the x-y plane. The axis of the magnet and its direction of motion is lined up with the center of the loop. What is the direction of the induced current through the resistor that is connected to the loop?

from a to b

In the figure, the inner loop carries a clockwise current III that is increasing. The resistor R is in the outer loop and both loops are in the same plane. The induced current through the resistor RRR is

from aaa to bbb.

In an inductor, energy is stored

in the magnetic field.

In the expression for Ampere's Law ∮𝐵⃗ ∙ 𝑑𝑠 = 𝜇0𝐼 , the integral is an instruction to:

integrate the magnetic field around a closed path

A beam of electrons enters a region with a magnetic field as shown. If the beam is deflected upward on the paper, the magnetic field must be oriented

into the plane of the drawing.

As shown in the figure, a proton (charge 𝑞p = +𝑒) passes through a region of magnetic field (shaded region). If the path of the proton is deflected as shown, the direction of the magnetic field must be

into the plane of the page.

The three loops of wire shown in the figure are all subject to the same uniform magnetic field B⃗ B→that does not vary with time. Loop 1 oscillates back and forth as the bob in a pendulum, loop 2 rotates about a vertical axis, and loop 3 oscillates up and down at the end of a spring. Which loop, or loops, will have an emf induced in them?

loop 2 only

The long straight wire in the figure carries a current III that is decreasing with time at a constant rate. The circular loops A, B, and C all lie in a plane containing the wire. The induced emf in each of the loops A, B, and C is such that

loop A has a counter-clockwise emf, loop B has no induced emf, and loop C has a clockwise emf. Submit

A circular loop of wire is positioned half in and half out of a square region of constant, uniform magnetic field directed into the page, as shown. To induce a clockwise current in the loop:

move it in the + x direction

The bottom plate of the capacitor to the right is being charged positively with current I. The radius of the plates is R and the distance between the plates is small compared to the radius. The magnetic field midway between the plates and at a distance of R/2 from the axis is closest to:

mu0I/4piR

Lenz' law states that the direction of an induced current in a closed conducting loop will:

oppose the change that produced it

For Questions 1 and 2 consider the following situation: an alpha-particle (an ionized helium atom with charge q = +2e, where e is the magnitude of the electron charge) is traveling along the positive x-direction until it enters a region of uniform magnetic field at the point a, at which point it travels a full half-circle of radius R and emerges from the magnetic field region at point b, but now traveling in the negative xdirection. The mass of an alpha-particle is 𝑚 = 6.68 × 10−27 kg.

out of the page

The diagram shows a straight wire carrying current i to the right in a uniform magnetic field. The magnetic force on the wire is down the paper as indicated by the arrow, but the magnetic field is not shown. Of the following possibilities, the direction of the magnetic field is:

out of the page

A circular loop of wire carries a current, i, in the counterclockwise direction, as shown in the sketch. As a result of the current, the magnetic field at point P, at the center of the loop, is:

out of the page.

Use the sketch to the right and this information to answer both questions 4 and 5. A positively charged particle of charge q=1.00x10-9 C, positioned at the origin (0,0) at time = 0, travels up the paper at velocity v=1.00x105 m/s as shown. The direction of the magnetic field at the point (-1,1) is

out of the paper

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 toward you, and the wire on your left carries current away from you. From your point of view, the magnetic field at the point exactly midway between the two wires

points downward.

The magnetic field at point P in the sketch for question A5:

points out of the paper.

A charge is accelerated from rest through a potential difference V and then enters a uniform magnetic field oriented perpendicular to its path. The magnetic field deflects the particle into a circular arc of radius R. If the accelerating potential is tripled to 3V, what will be the radius of the circular arc?

sqrt(3)*R

In the Biot-Savart relation to find the magnetic field at point P, 0 2 ˆ ( ) 4 Ids r B P r , the integral is over:

the length of the wire

For questions 7, 8, and 9, consider the situation depicted in the figure: a very thin, large square sheet (seen edge-on) of side length 𝐿 = 10 m carries a total current 𝐼 = 2.6 A distributed uniformly along its length into the page. The point P is at the center of the sheet, a distance 𝑑 = 0.050 m below it. The point 𝑃 ′ is also located at the center of the sheet, but a distance 𝑑 above it. The direction of the magnetic field created by the current sheet at the point 𝑃 is The direction of the magnetic field created by the current sheet at the point 𝑃 ′ is

to the left to the right

Use the figure to the right with the information here for questions 1 and 2. A current of 0.15 A flows in a clockwise direction in the rectangular loop shown to the right. The loop dimensions are 0.3 m horizontal length and 0.20 vertical height. The right half of the loop is in a uniform magnetic field of 0.50 T pointing into the paper. The direction of the net force on the loop is:

to the right.

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?

toward the west -rhr fingers in current direction and curl toward field vector, thumb points in direction of magnetic force

A resistor and an ideal inductor are connected in series to an ideal battery having a constant terminal voltage VVV 0.(a) At the moment contact is made with the battery, the voltage across the resistor is

zero.

A power supply delivers a sinusoidal voltage of amplitude V0 to a resistor R, independent of frequency f. The average power dissipated in the resistor is closest to:

𝑉0^2 /2𝑅.