Question 1

Which of the following statements best explains why a compass needle points north?

Accepted Answer

The north pole of the compass needle is attracted to the geographic North Pole, which is actually a magnetic south pole.

Question 2

A charged particle with charge $$q$$ and velocity $$\vec{v}$$ enters a uniform magnetic field $$\vec{B} at an $$angle $$	heta. $$What is the magnitude of the force acting on the particle?

Accepted Answer

$$F = qvB \sin 	heta$$

Question 3

Which of the following best describes the behavior of magnetic field lines?

Accepted Answer

They form closed loops from the north pole to the south pole and never cross each other.

Question 4

A long straight wire carries a current $$I. $$What is the magnitude of the magnetic field at a distance $$r$$ from the wire?

Accepted Answer

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

Question 5

Two parallel wires carry currents $$I_1$$ and $$I_2 in $$the same direction. What is the nature of the force between them?

Accepted Answer

They attract each other.

Question 6

A proton moves perpendicular to a uniform magnetic field $$B$$ with speed $$v. $$What is the radius of its circular path?

Accepted Answer

$$r = \frac{mv}{qB}$$

Question 7

A wire of length $$l$$ carries a current $$I$$ perpendicular to a uniform magnetic field $$B. $$What is the magnitude of the force on the wire?

Accepted Answer

$$F = IBl$$

Question 8

A rectangular coil with $$N$$ turns, area $$A$$, and current $$I is $$placed in a uniform magnetic field $$B. $$What is the maximum torque experienced by the coil?

Accepted Answer

$$	au_{max} = NIAB$$

Question 9

Which of the following is a correct application of the Hall Effect in modern technology?

Accepted Answer

Detecting the presence and magnitude of magnetic fields in sensors.

Question 10

A solenoid has $$N$$ turns, length $$l$$, and carries current $$I. $$What is the magnitude of the magnetic field inside the solenoid?

Accepted Answer

$$B = \mu_0$ \frac{N I}{l}$$

Question 11

A mass spectrometer separates ions based on their mass-to-charge ratio. If two ions have the same charge but different masses, how will their paths differ in the magnetic field?

Accepted Answer

The heavier ion will follow a path with a larger radius.

Question 12

Which of the following statements about ferromagnetic materials is correct?

Accepted Answer

Applying an external magnetic field aligns the domains, magnetizing the material.

Question 13

A current-carrying wire is placed in the Earth's magnetic field. Under what condition will the magnetic force on the wire be zero?

Accepted Answer

When the current is parallel to the magnetic field.

Question 14

Which equation correctly expresses Ampère’s Law for the magnetic field around a closed loop?

Accepted Answer

$$\sum \Delta B \cdot l = \mu_0$ I_{encl}$$

Question 15

A bar magnet is cut in half. What happens to the magnetic poles?

Accepted Answer

Each half becomes a smaller magnet with both a north and a south pole.

Question 16

A wire loop is placed in a uniform magnetic field. What is the direction of the torque on the loop if the current flows counterclockwise when viewed from above and the magnetic field points to the right?

Accepted Answer

The torque tends to rotate the loop so its normal vector aligns with the magnetic field.

Question 17

Which of the following best describes the origin of magnetism in materials?

Accepted Answer

It is caused by moving electric charges, such as electrons orbiting nuclei or spinning.

Question 18

A conducting bar moves with velocity $$v$$ perpendicular to a magnetic field $$B. $$What is the induced Hall voltage across the bar of width $$l$$?

Accepted Answer

$$\mathcal{E} = Bvl$$

Question 19

Which of the following is NOT a property of magnetic field lines?

Accepted Answer

They can cross each other at points where the field is strong.

Chapter 20: Magnetism: Principles, Forces, and Applications

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