MCAT Physical : Magnetic Fields

Study concepts, example questions & explanations for MCAT Physical

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Example Questions

Example Question #1 : Magnetism And Electromagnetism

Which of the following influences the emf produced in a wire loop that is rotating in a magnetic field?

Possible Answers:

More than one of the other options is correct

The material of which the loop is made

The shape of the loop

The resistance of the loop

The size of the loop

Correct answer:

The size of the loop

Explanation:

Recall that , where . The shape, material characteristics, and resistance do not appear in this equation. So only the size (area) of the loop influences the emf.

Example Question #5 : Magnetism And Electromagnetism

Which of the following best describes magnetic field lines?

Possible Answers:

They show both the relative strength and direction of the magnetic field

They show the direction in which a positive charge will experience a force

They can only cross when multiple magnets are present

More than one of the other options is correct

They always begin at a north pole and terminate at a south pole

Correct answer:

They show both the relative strength and direction of the magnetic field

Explanation:

First, magnetic field lines, like electric field lines, can never cross. Also, unlike electric field lines, magnetic field lines are continuous—they do not have starting or ending points. Next, the force experienced by a charge in a magnetic field depends on the charge's velocity direction, not just the magnetic field. So the only remaining choice is that magnetic field lines show both the relative strength and direction of the field.

Example Question #1 : Magnetic Fields

A  current-carrying wire is placed in a uniform magnetic field oriented perpendicularly to the wire. The length of the wire is  and the magnitude of the magnetic field is . What is the force on the wire?

Possible Answers:

Correct answer:

Explanation:

We use the formula for force on a wire in a magnetic field:

Where  = force,  = current,  = length of wire, and  = magnetic mield

Example Question #2 : Magnetic Fields

A scientist builds a particle accelerator. Which of the following would not help the scientist increase the speed of a particle in the accelerator?

Possible Answers:

Increasing the radius that the particles spin around

Increasing the mass of the particles in the accelerator

Decreasing the temperature of the particle accelerator

Increasing the strength of the magnetic field

Increasing the charge of the particles 

Correct answer:

Increasing the mass of the particles in the accelerator

Explanation:

A charged particle in a particle accelerator moves in uniform circular motion. The equation for centripetal force caused by uniform circular motion is:

The equation for magnetic force is:

Set the equations equal to each other, and solve for velocity.

The only answer choice that does not correspond to an increase in velocity is increasing the mass of the particles in the accelerator.

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