Q: A proton moves at $$5.0 \times 10^6$ m/s in a magnetic field of 0.40$ T at an angle of 30$$^\circ$$ to the field. What is the magnitude of the force on the proton? (Proton charge q = 1.6$$ \times $$10^{-19} C)$$

$$F = 1.6 \times 10$$^{-13}$$ N

Question 1

Which statement best describes the direction of the magnetic field at a given point near a bar magnet?

Accepted Answer

It is the direction indicated by the north pole of a small compass needle placed at that point.

Question 2

A charged particle moves with velocity $$\vec{v} in a $$region with a uniform magnetic field $$\vec{B}. $$Which condition must be met for the particle to experience a magnetic force?

Accepted Answer

The particle must be moving and its velocity must have a component perpendicular to $$\vec{B}.$$

Question 3

What is the correct formula for the magnitude of the magnetic force $$F on a $$charge $$q$$ moving with velocity $$v at an $$angle $$	heta to a $$magnetic field $$B$$?

Accepted Answer

$$F = qvB \sin 	heta$$

Question 4

A proton moves at $$5.0 	imes 10^6$ m/s in a magnetic field of 0.40$ T at an angle of 30$$^\circ$$ to the field. What is the magnitude of the force on the proton? (Proton charge q = 1.6$$ 	imes $$10^{-19} C)$$

Accepted Answer

$$F = 1.6 	imes 10$$^{-13}$$ N

Question 5

Which of the following statements about magnetic field lines is correct?

Accepted Answer

They form closed loops, never beginning or ending.

Question 6

If a charged particle moves perpendicular to a uniform magnetic field, what is the shape of its trajectory?

Accepted Answer

It moves in a circular path.

Question 7

What is the radius $$r of $$the circular path for a particle of mass $$m$$, charge $$q$$, velocity $$v$$, in a magnetic field $$B$$?

Accepted Answer

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

Question 8

A velocity selector uses both electric and magnetic fields to allow only particles of a certain velocity to pass through undeflected. What is the relationship between the electric field $$E$$, magnetic field $$B$$, and velocity $$v$$?

Accepted Answer

$$v = \frac{E}{B}$$

Question 9

Why can't the magnetic force do work on a charged particle?

Accepted Answer

Because the magnetic force is always perpendicular to the velocity, so no displacement occurs along the direction of the force.

Question 10

In a mass spectrometer, ions are accelerated and then enter a region with a magnetic field. If two ions have the same charge but different masses, how will their paths differ?

Accepted Answer

The ion with greater mass will have a larger radius of curvature.

Question 11

A negative charge moves in a magnetic field. Using the right hand rule, how do you determine the direction of the force?

Accepted Answer

The force is opposite to the direction of the thumb.

Question 12

The Earth's magnetic field axis is not aligned with its rotational axis. What is the angle between these axes?

Accepted Answer

11.5 degrees

Question 13

A fast electron with speed $$2.0 	imes 10^7$ m/s moves in the Earth's magnetic field (B = 0.5$$ 	imes $$10^{-4} T). $$What is the radius of curvature of its path? (Electron mass $$m = 9.11 	imes 10$$^{-31}$$ kg, charge q = 1.6$$ 	imes $$10^{-19} C)$$

Accepted Answer

$$r = 2.3 m$$

Question 14

Which of the following best describes the behavior of like and unlike magnetic poles?

Accepted Answer

Like poles repel, unlike poles attract.

Question 15

In a bubble chamber, a gamma ray transforms into two charged particles. If the magnetic field is directed out of the paper, what can be inferred about the sign of the particles from their spiral tracks?

Accepted Answer

The particles have opposite signs.

Question 16

Which of the following is the SI unit for magnetic field strength?

Accepted Answer

Tesla

Question 17

A mass spectrometer measures the masses and relative abundances of isotopes. For neon, which isotope is most abundant according to the mass spectrum?

Accepted Answer

Neon-20

Question 18

Which equation correctly relates the kinetic energy gained by an ion accelerated through a potential difference $$V in a $$mass spectrometer?

Accepted Answer

$$KE = qV$$

Question 19

If a charged particle moves parallel to a magnetic field, what is the magnetic force acting on it?

Accepted Answer

Zero force

Question 20

Which of the following best explains why separate north or south magnetic poles do not exist in nature?

Accepted Answer

Magnetic field lines form closed loops, so isolated poles cannot exist.

Lec 10

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