Question 1

A mass spectrometer is used to analyze a sample of neon. The output shows three peaks at atomic mass numbers 20, 21, and 22. What does the relative height of these peaks indicate?

Accepted Answer

The relative abundance of each isotope in the sample

Question 2

In a mass spectrometer, ions are accelerated through a potential difference $$V$$ and then enter a region with a perpendicular magnetic field $$B. If $$the radius of the ion's path is $$r$$, which equation correctly relates the mass $$m of $$the ion to the measured quantities?

Accepted Answer

$$m = \frac{qB^2$r^2$$}{2V}$

Question 3

A straight wire of length $$L$$ carries a current $$I$$ and is placed in a uniform magnetic field $$B at an $$angle $$	heta to $$the field. What is the magnitude of the force on the wire?

Accepted Answer

$$F = ILB\sin	heta$$

Question 4

A 2.0 m long wire carries a current of 20 A eastward and is placed in the Earth's magnetic field of $$0.5 	imes 10$$^{-4}$$ T pointing north. What is the magnitude of the force on the wire?

Accepted Answer

$$2.0 	imes 10$$^{-3}$$ N

Question 5

Which right-hand rule is used to determine the direction of the force on a current-carrying wire in a magnetic field?

Accepted Answer

Point your thumb in the direction of the current, fingers in the direction of the magnetic field, and your palm points in the direction of the force.

Question 6

A 1000 kg MHD-powered boat generates a 1.0 T magnetic field and a current of 100 A across plates separated by 2.0 m. What is the electric power required to operate the boat if the voltage across the plates is 20 V?

Accepted Answer

$$P = 2000 W$$

Question 7

The magnetic field at a distance $$r$$ from a long, straight wire carrying current $$I is $$given by:

Accepted Answer

$$B = \frac{\mu_0$ I}{2\pi r}$$

Question 8

Two parallel wires, each 1.0 m long and separated by 7.0 cm, carry equal currents and repel each other such that one wire is levitated. If the mass of each wire is 0.5 kg, what is the required current in each wire?

Accepted Answer

$$I = 1300 A$$

Question 9

A solenoid is 0.25 m long, has 5000 turns, and carries a current of 3.5 A. What is the magnetic field inside the solenoid?

Accepted Answer

$$B = 0.088 T$$

Question 10

A voice coil in a loudspeaker has a diameter of 0.025 m, contains 55 turns, and is placed in a 0.10 T magnetic field. If the current is 2.0 A, what is the magnitude of the force on the coil?

Accepted Answer

$$F = 0.86 N$$

Question 11

The torque on a current-carrying coil of $$N$$ turns, area $$A$$, in a magnetic field $$B at an $$angle $$\phi is$$:

Accepted Answer

$$	au = NIAB\sin\phi$$

Question 12

A charged particle with charge $$q$$ moves with velocity $$v$$ parallel to a long straight wire carrying current $$I. If $$the particle is at a distance $$r$$ from the wire, what is the magnitude of the magnetic force on the particle?

Accepted Answer

$$F = qv \frac{\mu_0$ I}{2\pi r}$$

Question 13

Which of the following best describes the function of a split-ring commutator in a DC motor?

Accepted Answer

It reverses the direction of current in the coil every half turn to maintain continuous rotation.

Question 14

In a galvanometer, the angular displacement $$\Delta\phi of $$the needle is proportional to the current $$I$$ because:

Accepted Answer

The magnetic torque is balanced by the spring torque: $$NIAB\sin\phi = k\Delta\phi$$

Question 15

A current-carrying wire is placed perpendicular to a uniform magnetic field. If the current is doubled and the length of the wire is halved, how does the force on the wire change?

Accepted Answer

It doubles.

Question 16

Which of the following statements about the magnetic field inside a long solenoid is correct?

Accepted Answer

It is uniform and given by $$B = \mu_0$ n I.$$

Question 17

A rectangular coil of wire with area $$A$$ and $$N$$ turns carries a current $$I$$ and is placed in a uniform magnetic field $$B. If $$the plane of the coil is perpendicular to the field, what is the torque on the coil?

Accepted Answer

$$	au = 0$$

Lecture 11

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