Physics 2 test 2 conceptual

The current carried by wire A is twice the current carried by the identical wire B. In which wire do the charge carriers have the higher drift speed?

WireA

WireB

Wire C

They have the same drift speed.

Wire A

The current carried by wire A is twice the current carried by the identical wire B. Which wire has the higher current density?

Answer options:

Wire A

Wire B

Wire C

They have the same current denisty

Wire A

Two wires are made of the same material, but Wire A is twice as long and has twice the radius of Wire B. How does the resistance of A compare to B?

Answer options:

Resistance of Wire A is equal to Wire B.

Resistance of Wire A is greater than Wire B.

Resistance of Wire A is less than Wire B.

Resistance of Wire A is less than Wire B.

The terminal voltage is always less than or equal to the emf for a real battery.

Answer options:

True

False

True

For which case(s) do you expect the discharging time to increase for a given system?

Answer options:

Increase resistance.

Increase capacitance.

Decrease resistance.

Decrease capacitance.

Increase resistance.

Increase capacitance

For a discharging RC circuit, we expect both charge on the capacitor and system current to decrease over time.

Answer options:

True

False

True

For a charging RC circuit, we expect both charge on the capacitor and system current to increase over time.

Answer options:

True

False

False

In what direction is the magnetic force on the moving positively charged particle?( voltage vector traveling up, and the blue magnetic field is going right

Answer options:

Toward the Top of the Screen

Toward the Bottom of the Screen

To the Left

To the Right

Into the Screen

Out of the Screen

Into the screen

In what direction is the magnetic force on the moving negatively charged particle?(V is going into the screen and B is going upward)

Answer options:

Toward the Top of the Screen

Toward the Bottom of the Screen

To the Left

To the Right

Into the Screen

Out of the Screen

Left

In what direction is the magnetic force on the moving negatively charged particle?(B is going left and V is going out of the screen)

Answer options:

Toward the Top of the Screen

Toward the Bottom of the Screen

To the Left

To the Right

Into the Screen

Out of the Screen

Top

Since the magnetic force is always perpendicular to the particle's velocity, magnetic forces do ______ work on particles.

Answer options:

zero

positive

negative

Zero

A current-carrying loop is placed in a uniform magnetic field. How does the magnetic torque on the loop behave?

Answer options:

The torque is zero if the magnetic field is parallel to the plane of the loop.

The torque is maximum when the magnetic field is parallel to the loop's magnetic moment.

The torque seeks to align the loop to be perpendicular to the magnetic field.

The torque does not depend on the orientation of the loop relative to the field.

The torque seeks to align the loop to be perpendicular to the magnetic field.

In the Hall effect, what is the primary reason a potential difference is developed across the conductor?

Answer options:

The magnetic field induces an electric field across the conductor.

The charge carriers experience a force perpendicular to both the magnetic field and current.

The current increases in the presence of the magnetic field.

The conductor's resistance decreases due to the magnetic field.

The charge carriers experience a force perpendicular to both the magnetic field and current.

A point charge is moving with a constant velocity. What best describes the magnetic field it generates?

Answer options:

The magnetic field is strongest along the direction of motion of the charge.

The magnetic field is circular around the path of the moving charge.

The magnetic field is uniform and does not depend on the speed of the charge.

The magnetic field exists only if the charge is accelerating.

The magnetic field is circular around the path of the moving charge.

Which of the following best describes the magnetic field inside a long, current-carrying solenoid?

Answer options:

The interior magnetic field is non-uniform and decreases along the length of the solenoid.

The interior magnetic field is uniform and directed parallel to the axis of the solenoid.

The magnetic field is strongest outside the solenoid and weaker inside.

The interior magnetic field is uniform and directed parallel to the axis of the solenoid.

The two wires shown carry equal and opposite currents. At the midpoint between the currents, the magnetic field is...(dot in the middle of two parallel lines the left line has I going down and the right line has I going up)((|*|))

Answer options:

Zero

Into the Screen

Out of the Screen

Toward the Top of the Screen

Toward the Bottom of the Screen

Out of the Screen

If instead, the currents were in the same direction: At the midpoint between the currents, the magnetic field is...(dot in the middle of two parallel lines the left line has I going down and the right line has I going up)((|*|))

Answer options:

Zero

Into the Screen

Out of the Screen

Toward the Top of the Screen

Toward the Bottom of the Screen

Zero

Two parallel wires carry current in the same direction. Wire 1 has current I while wire 2 [has] double the current. Which wire experiences greater force?

Answer options:

Wire 1

Wire 2

They experience the same magnitude force.

They experience the same magnitude force.

When a current is passed through the wire in the figure, will the wire tend to bunch up or will it tend to form a circle?(figure is a wire that is in a random asymmetric shape)

Answer options:

Bunch Up

Form a Circle

Not enough information

Form a Circle

The magnetic field strength is always changes as a function of inverse distance.

Answer options:

True

False

False

Which of the following statements is true about the application of Ampere's Law?

Answer options:

Ampere's Law can only be applied if the current distribution is uniform.

Ampere's Law applies only to circular paths.

Ampere's Law cannot be used when there is no current enclosed.

None of these.

None of these.

In which direction is the induced emf/current?(v and the south end of a magnet is going TOWARD a closed loop)

Answer options:

Clockwise

Counter-Clockwise

No Induced Current

Clockwise

In which direction is the induced emf/current?(v and the south end of a magnet is going AWAY from the closed loop)

Answer options:

Clockwise

Counter-Clockwise

No Induced Current

Clockwise

In which direction is the induced emf/current?(North end of a magnet pointing toward a closed loop with V going counterclockwise along the closed loop)

Answer options:

Clockwise

Counter-Clockwise

No Induced Current

No Induced Current

Wires A and B are both made of copper. The wires are connected in series, so we know they carry the same current. However, the diameter of wire A is twice the diameter of wire B. Which wire has the higher number density of charge carriers (number per unit charge)?

(a) A,

(b) B,

(c) They have the same number density of charge carriers.

Answer: (c) They have the same number density of charge carriers.

Brief Explanation: The number density of charge carriers is a material property. Since both wires are made of copper, their intrinsic electron density remains the same regardless of the wire diameter.

The diameters of copper wires A and B are equal. The current carried by wire A is twice the current carried by wire B. In which wire do the charge carriers have the higher drift speed?

(a) A,

(b) B,

(c) They have the same drift speed.

Answer: (a) A

Brief Explanation: The drift speed vd is given by vd=I/nqA Since both wires have the same diameter (hence the same cross-sectional area A) and the same material (same n and q, the wire with the higher current (wire A) must have a higher drift speed.

Wire A and wire B are identical copper wires. The current carried by wire A is twice the current carried by wire B. Which wire has the higher current density? (a) A, (b) B, (c) They have the same current density. (d) none of the above

Answer: (a) A

Brief Explanation: Since the wires are identical, they have the same cross-sectional area. Current density J is defined as J=I/A​. With wire A carrying twice the current of wire B, its current density is also twice as high.

Consider a metal wire that has each end connected to a different terminal of the same battery. Your friend argues that no matter how long the wire is, the drift speed of the charge carriers in the wire is the same. Evaluate your friend's claim.

Answer: The friend's claim is incorrect.

Brief Explanation: For a given battery, a longer wire has a higher resistance (since R=ρ(L/A), leading to a lower current (I=VR​). Because drift speed vd=I/nqA depends on the current, a longer wire results in a lower drift speed compared to a shorter wire with the same material and cross-sectional area.

In a resistor, the direction of the current must always be in the "downhill" direction, that is, in the direction of decreasing electric potential. Is it also the case that in a battery, the direction of the current must always be the "downhill"? Explain your answer.

Answer: No, it is not always "downhill" in a battery.

Brief Explanation: In a resistor, current flows from a higher to a lower potential, following the "downhill" direction. However, inside a battery, chemical reactions do work on the charge carriers, effectively "pushing" them from a lower potential to a higher potential. Thus, while the external circuit current flows "downhill" from the positive to the negative terminal, inside the battery the current is driven "uphill" against the potential gradient.

Discuss the distinction between an emf and a potential difference.

Answer: An emf (electromotive force) is the energy supplied per unit charge by a source (like a battery) that drives charge around a circuit, while a potential difference is the voltage drop measured across components (such as resistors) due to energy dissipation.

Brief Explanation: The emf represents the work done to move a charge through the energy conversion process inside the battery (or generator), even in the absence of current, whereas the potential difference is the loss of energy per charge as it passes through circuit elements.

Wire A and wire B are made of the same material and have the same length. The diameter of wire A is twice the diameter of wire B. If the resistance of wire B is R, then what is the resistance of wire A? (Neglet any effects that temperature may have on resistance.)

(a) R,

(b) 2R,

(c) R/2,

(d) 4R,

(e) R/4

Answer: (e) R/4

Brief Explanation: Resistance is given by R=ρ(L/A). Doubling the diameter of a wire quadruples its cross-sectional area A (since A∝d^2). With the same length and material, the resistance becomes one-fourth that of the original wire.

Two cylindrical copper wires have the same mass. Wire A is twice as long as wire B. (Neglet any effects that temperature may have on resistance.) Their resistances are related by

(a) RA=8RB,

(b) RA=4RB,

(c) RA=2RB,

(d) RA=RB

Answer: (b) RA = 4RB

Brief Explanation:For a cylindrical wire, resistance is given by R = rho L / A, where rho is resistivity, L is length, and A is cross-sectional area. Since both wires have the same mass, their volumes are equal. That is, A_A L_A = A_B L_B. Given that wire A is twice as long as wire B (L_A = 2 L_B), the cross-sectional area of wire A must be half that of wire B (A_A = A_B/2).Now, substitute into the resistance formula for wire A:RA = rho (2 L_B) / (A_B/2) = 4 (rho L_B / A_B) = 4RB.

If the current in a resistor is I, the power delivered to the resistor is P. If the current in the resistor is increased to 3I, what is the power then delivered to the resistor? (Assume the resistance of the resistor does not change.)

(a) P,

(b) 3P,

(c)P/3,

(d) 9P,

(e)P/9

Answer: (d) 9P

Brief Explanation:The power delivered to a resistor is given by the formula P = I^2 R. If the current is increased to 3I, then the new power is P_new = (3I)^2 R = 9I^2 * R, which equals 9P.

An electron moving in the +x direction enters a region that has a uniform magnetic field in the +y direction. When the electron enters this region, it will

(a) be deflected toward the +y direction,

(b) be deflected toward the -y direction,

(c) be deflected toward the +z direction,

(d) be deflected toward the -z direction,

(e) continue undeflected in the +xdirection.

Answer:(d) be deflected toward the -z direction,

Brief Explanation:X x y=z which puts it in the z direction but an election has a negative charge so its actually in the -z direction

True or false:

The magnetic moment of a bar magnet points from its north pole to its south pole.

False

Brief Explanation: The magnetic moment of a bar magnet is defined as pointing from the south pole to the north pole

True or false:

Inside the material of a bar magnet, the magnetic field due to the bar magnet points from the magnet's south pole toward its north pole.

True

Brief Explanation: Inside a bar magnet, the magnetic field lines run from the south pole toward the north pole.

True or false:

If a current loop simultaneously has its current doubled and its area cut in half, then the magnitude of its magnetic moment remains the same.

True

Brief Explanation: The magnetic moment is given by mu = I * A; doubling I and halving A leaves mu unchanged

True or false:

The maximum torque on a current loop placed in a magnetic field occurs when the plane of the loop is perpendicular to the direction of the magnetic field.

False

Brief Explanation: Maximum torque occurs when the magnetic moment is perpendicular to the magnetic field, which happens when the plane of the loop is parallel—not perpendicular—to the field.

Parallel wires 1 and 2 carry currents I1​ and I2 respectively, where I2 = 2I1​. The two currents are in the same direction. The magnitudes of the magnetic force by current 1 on wire 2 and by current 2 on wire 1 are F12​ and F21, respectively. These magnitudes are related by:

Answer options:

(a) F12=F21

​(b) F21=2F12

​(c) 2F21=F12

​(d) F21=4F12​

e) 4F21=F12​

F12 = F21

You are facing directly into one end of a long solenoid and the magnetic field inside of the solenoid points away from you. From your perspective, is the direction of the current in the solenoid coils clockwise or counterclockwise? Explain your answer.

Answer: clockwise

Brief Explanation:Using the right-hand grip rule for a solenoid, point your thumb in the direction of the magnetic field (which is away from you). Your fingers will curl in the direction of the current. When you are looking into the solenoid, this curl appears as clockwise.

Opposite ends of a helical metal spring are connected to the terminals of a battery. Do the spacings between the coils of the spring tend to increase, decrease, or remain the same when the battery is connected? Explain your answer.

Answer: The spacings between the coils tend to decrease.

Brief Explanation: When the battery is connected, current flows through the spring, making each coil act like a current loop. The magnetic fields created by these loops are aligned and produce attractive forces between adjacent coils. These forces pull the coils toward each other, causing the spacing between them to decrease.

The current density is constant and uniform in a long, straight wire that has a circular cross section. True or false:

(A)The magnitude of the magnetic field produced by the wire is greatest at the surface of the wire.

(B)The magnetic field strength in the region surrounding the wire varies inversely with the square of the distance from the wire's central axis.

(C)The magnetic field is zero at all points on the wire's central axis.

(D)The magnitude of the magnetic field inside the wire increases linearly with the distance from the wire's central axis.

True

Brief Explanation: Inside the wire, the magnetic field increases linearly with distance from the axis, reaching its maximum at the surface.

False

Brief Explanation: In the region outside the wire, the magnetic field varies inversely with distance (1/r), not with the square of the distance (1/r²).

True

Brief Explanation: On the wire's central axis, the distance r = 0, which means the magnetic field is zero.

True

Brief Explanation: With a constant, uniform current density, the magnetic field inside the wire follows B ∝ r, so it increases linearly with the distance from the central axis.

A current is induced in a conducting loop that lies in a horizontal plane, and the induced current is clockwise when viewed from above. Which of the following statements could be true?

(a) A constant magnetic field is directed vertically downward.

(b) A constant magnetic field is directed vertically upward.

(c) A magnetic field whose magnitude is increasing is directed vertically downward.

(d) A magnetic field whose magnitude is decreasing is directed vertically downward.

(e) A magnetic field whose magnitude is decreasing is directed vertically upward.

Answer: (d) A magnetic field whose magnitude is decreasing is directed vertically downward.

Brief Explanation:When you view the loop from above, a clockwise induced current produces an induced magnetic field that points downward (using the right-hand rule). By Lenz's law, the induced field opposes the change in magnetic flux. If the external magnetic field is directed downward but its magnitude is decreasing, the downward flux through the loop is decreasing. The induced current then produces a downward field to oppose this decrease.

A small square wire loop lies in the plane of this page, and a constant magnetic field is directed into the page. The loop is moving to the right, which is the +x direction. Find the direction of the induced current, if any, in the loop if (a) the magnetic field is uniform,

(b) the magnetic field strength increases as x increases, and

(c) the magnetic field strength decreases as x increases.

(a) No induced current

Brief Explanation: With a uniform magnetic field, the flux through the loop remains constant as it moves, so no current is induced.

(b) Counterclockwise induced current

Brief Explanation: As the loop moves right into a region where the magnetic field (directed into the page) increases, the flux into the page increases. To oppose this increase (per Lenz's law), the induced current generates a magnetic field out of the page. Using the right-hand rule, this requires a counterclockwise current.

(c) Clockwise induced current

Brief Explanation: Here, the loop moves right into a region where the magnetic field (directed into the page) decreases, so the flux into the page decreases. To oppose this decrease, the induced current must create a magnetic field into the page. The right-hand rule shows that a clockwise current produces a magnetic field into the page.

If the current in an inductor doubles, the energy stored in the inductor will

(a) remain the same,

(b) double,

(c) quadruple,

(d) halve.

Answer: (c) quadruple

Brief Explanation: The energy stored in an inductor is given by E = (1/2) L I^2. If the current doubles, then E' = (1/2) L (2I)^2 = 4 [(1/2) L * I^2], so the energy becomes four times greater.

Two solenoids are equal in length and radius, and the cores of both are identical cylinders of iron. However, solenoid A has three times the number of turns per unit length as solenoid B.

(a) Which solenoid has the larger self-inductance?

(b) What is the ratio of the self-inductance of solenoid A to the self-inductance of solenoid B?

(a) Solenoid A has the larger self-inductance.

(b) The ratio L_A : L_B is 9 : 1.

Brief Explanation:For a solenoid, the self-inductance is given by L = μ n² A l, where μ is the permeability, n is the number of turns per unit length, A is the cross-sectional area, and l is the length. Since solenoid A has three times as many turns per unit length (n_A = 3n_B) and both solenoids have the same A and l, its inductance is L_A = μ (3n_B)² A l = 9 μ n_B² A l = 9L_B.

True or false:

(A) The induced emf in a circuit is equal to the negative of the magnetic flux through the circuit.

(B) There can be a nonzero induced emf at an instant when the flux through the circuit is equal to zero.

(C) The self-inductance of a solenoid is proportional to the rate of change of the current in the solenoid.

(D) The magnetic energy density at some point in space is proportional to the square of the magnitude of the magnetic field at that point.

(E)The inductance of a solenoid is proportional to the current in it

False

Brief Explanation: The induced emf is equal to the negative rate of change of the magnetic flux, not the negative of the flux itself.

True

Brief Explanation: Even if the instantaneous flux is zero, its rate of change may be nonzero, which can produce a nonzero induced emf.

False

Brief Explanation: The self-inductance is a property of the coil's geometry and material (L = μ n² A l for a solenoid) and is independent of the rate at which the current changes. It is the induced emf that is proportional to the rate of change of the current (emf = -L dI/dt).

True

Brief Explanation: The magnetic energy density is given by u = B²/(2μ₀) (or a similar expression in materials), showing that it is proportional to the square of the magnetic field.

False

Brief Explanation: The inductance of a solenoid is determined by its physical characteristics (geometry, number of turns, core material) and does not vary with the current passing through it.