Quick Quizzes: Chapter's 19, 20, & 21

A charged particle moves in a straight line through a region of space. Which of the following answers must be true? (Assume any other fields are negligible.) The magnetic field:

Has a zero component perpendicular to the particle’s velocity

The north-pole end of a bar magnet is held near a stationary positively charged piece of plastic. The plastic is:

Unaffected by the magnet

As a charged particle moves freely in a circular path in the presence of a constant magnetic field applied perpendicular to the particle’s velocity, the particle’s kinetic energy:

Remains constant

A square and a circular loop with the same area lie in the xyz-plane, where there is a uniform magnetic field B pointing at some angle θ with respect to the positive z-direction. Each loop carries the same current, in the same direction. Which magnetic torque is larger?

The torques are the same

Which of the following actions would double the magnitude of the magnetic force per unit length between two parallel current-carrying wires? Choose all correct answers.

Double one of the currents

Reduce the distance of them by half

I1 = 2A and I2 = 6A, which of the following is true? (Note that F2 represents the magnitude of the force on wire 2.)

F1= F2

Figure 20.6 is a graph of the magnitude versus time for a magnetic field that passes through a fixed loop and is oriented perpendicular to the plane of the loop. Rank the magnitudes of the emf generated in the loop from largest to smallest at the three instants indicated.

b, c, a

A bar magnet is falling toward the center of a loop of wire, with the north pole oriented downward. Viewed from the same side of the loop as the magnet, as the north pole approaches the loop, what is the direction of the induced current?

Counterclockwise

Two circular loops are side by side and lie in the xy-plane. A switch is closed, starting a counterclockwise current in the left-hand loop, as viewed from a point on the positive z-axis passing through the center of the loop. Which of the following statements is true of the right-hand loop?

An induced current moves counterclockwise

A horizontal metal bar oriented east–west drops straight down in a location where Earth’s magnetic field is due north. As a result, an emf develops between the ends. Which end is positively charged?

The east end

You intend to move a rectangular loop of wire into a region of uniform magnetic field at a given speed so as to induce an emf in the loop. The plane of the loop must remain perpendicular to the magnetic field lines. In which orientation should you hold the loop while you move it into the region with the magnetic field to generate the largest emf?

With the short dimension of the loop parallel to the velocity vector

Which of the following statements can be true for a resistor connected in a simple series circuit to an operating AC generator?

P_av > 0

i_av = 0

If switch A is closed in Figure 21.12, what happens to the impedance of the circuit?

It decreases

Suppose XL > XC in Figure 21.12. If switch A is closed, what happens to the phase angle?

It increases

In an apparatus such as the one in Figure 21.22, suppose the black disk is replaced by one with half the radius. Which of the following are different after the disk is replaced?

Radiation force on the disk

Radiation momentum delivered to the disk in a given time interval

Which of the following statements are true about light waves?

The lower the frequency, the longer the wavelength

The shorter the wavelength, the higher the frequency