Physics CH 19- Magnet Forces and Fields

A long, straight wire carries a current of 1.0 A. What is the magnitude of the magnetic force on a 2.0 m section of the wire when placed in a uniform 0.10 T magnetic field that is parallel to the wire?

0 N

A space beacon emits radio waves with a frequency of 1.00 MHz. A spaceship recedes from the beacon. The relative speed between the spaceship and the beacon is one-third the speed of light. Identify the frequency measured by an observer on the spaceship.

0.707 MHz

Rank the following electromagnetic waves traveling in vacuum according to electric field amplitude, with the largest electric field amplitude at the top and the smallest at the bottom.

1. 0.10 T 2. 0.010 T 3. 10 V/m 4. 1.0 V/m

Rank the following electromagnetic waves traveling in vacuum according to magnetic field amplitude, with the largest magnetic field amplitude at the top and the smallest at the bottom.

1. 5.50 T 2. 0.030 T 3. 25 V/m 4. 0.055 V/m

Rank the magnitude of the magnetic force for each scenario below, with the largest at the top and the smallest at the bottom. Assume the particles all move with the same speed and the magnetic field is the same in all cases. Instructions

1. Electron moving perpendicular to magnetic field 2. Proton moving at 45 to magnetic field 3. Electron moving at 30 to magnetic field 4. Proton moving parallel to magnetic field

A space beacon emits radio waves with a frequency of 1.00 MHz. A spaceship approaches the beacon. The relative speed between the spaceship and the beacon is one-third the speed of light. What frequency does an observer on the spaceship measure?

1.41 MHz

Select all of the following that are not possible values for the index of refraction.

1.5 m/s 3.00 x 108 m/s

A wire is 10 cm long and 5 mm in radius. What is the magnitude of the length vector for this wire?

10 cm

A radio station broadcasts its signal using an electric dipole antenna that is oriented vertically. Select all of the following locations where the amplitudes of the emitted electric and magnetic fields would be the largest.

10 meters to the left of the antenna 10 meters to the right of the antenna

A radio station broadcasts its signal using an magnetic dipole antenna, the axis of which is oriented vertically. Select all of the following locations where the amplitudes of the emitted electric and magnetic fields would be the largest.

10 meters to the left of the antenna 10 meters to the right of the antenna

Which of the following is equal to 1 N/(A⋅cm)?

100 T

What is the definition of wave number?

2π divided by the wavelength

Select all of the following statements that are correct.

A compass always points toward Earth's magnetic south pole. The position of Earth's magnetic poles change slowly over the years. The Earth's magnetic north pole is near its geographic South Pole.

What will an electron do if it is moving along the positive x-axis and enters a region where the magnetic field is perpendicular to the x-axis?

Accelerate

Select all of the following that would result in the emission of electromagnetic waves.

Accelerating proton Electron moving with uniform circular motion Oscillating electron Oscillating proton

Three current-carrying coils are described below. If each coil carries the same current, then which coil experiences the greatest torque magnitude when placed in identical magnetic fields such that the direction of the field is parallel to the plane of the coil?

All three coils experience the same torque magnitude.

Which of Maxwell's equations relates changing electric flux to magnetic fields?

Ampere-Maxwell law

What is the Earth's magnetic south pole near?

Arctic Ocean

What is the definition of intensity when light hits a surface at normal incidence?

Average power per unit area

What is the direction of the magnetic force on a straight wire in a uniform magnetic field pointing up toward the sky if the direction of the current is to the left?

Away from you

Which choice best represents the direction in which a compass needle points when placed near a bar magnet at a point marked by ⊕ in the figure?

B

What is the magnitude of the magnetic field inside a solenoid?

B = μonI

The Hall effect is the principle behind the _______ _______ , a common device used to measure magnetic fields.

Blank 1: Hall Blank 2: probe

Which fields are used in cyclotrons?

Both electric and magnetic

Two ions, each with the same charge and the same speed, move with uniform circular motion in a mass spectrometer. The mass of ion A is twice the mass of ion B. Select all of the following statements that are true.

Both ions accelerate. The radii of curvature of the circular paths are not equal. The magnitudes of their accelerations are not equal.

Consider an electron and a proton moving with the same velocity entering a region of uniform magnetic field. Which statement is true?

Both particles experience the same magnetic force magnitude.

Select all of the following quantities that help determine the magnetic force on a particle moving in a constant and uniform magnetic field.

Charge Velocity

If coils A, B, and C (described below) carry currents of 1 A, 2 A, and 3 A, respectively, then which coil experiences the greatest torque magnitude when placed in identical magnetic fields such that the direction of the field is parallel to the plane of the coil?

Coil C: square coil having 100 loops with sides of 10 cm

What causes the aurora borealis (northern lights)?

Cosmic rays and the solar wind

To which direction is the direction of the length vector always equal?

Current flow

As the current in a long, straight wire decreases, will the magnetic field magnitude at point Q, a distance of 4 m away from the wire, increase, decrease, or stay the same?

Decrease

What is the definition of wavelength?

Distance for one cycle

An electron is moving to the east in a uniform magnetic field that is directed to the north. In which direction is the magnetic force on the electron?

Down

What causes the concentration of charged particles from the Sun that spiral near the Earth's north and south poles?

Earth's magnetic field

Which types of monopoles have been experimentally detected?

Electric only

Select all of the following particles that experience a magnetic force.

Electron moving perpendicular to a magnetic field Proton moving at 30° to a magnetic field

Select all of the following that could emit electromagnetic waves.

Electrons Protons

What is the definition of energy density?

Energy per unit volume

True or false: The Earth's magnetic field is the same today as it was 100 years ago.

False

True or false: The Sun does not emit ultraviolet light.

False

True or false: The magnitude of the magnetic force on a current-carrying wire is largest when the field and wire are parallel to each other.

False

True or false: The speed of an electromagnetic wave in vacuum depends on its frequency and amplitude.

False

Three materials are placed in a magnetic field, then removed. Which of the following will be magnetized after they have been removed?

Ferromagnetic material

A circularly polarized light wave is the superposition of two light waves. Select all of the following properties that are the same for both of these light waves.

Frequency Amplitude

Select all of the following properties of the electric and magnetic fields in traveling electromagnetic waves that are always equal.

Frequency Wavelength

Which of Maxwell's equations states that charge creates electric fields?

Gauss's law

Which of Maxwell's equations states that there is no such thing as magnetic monopoles?

Gauss's law for magnetism

Select all of the following media in which dispersion occurs for EM waves.

Glass Water

As the current in a long, straight wire increases, will the magnetic field magnitude at point P, a distance of 1 m away from the wire, increase, decrease, or stay the same?

Increase

A current carrying wire is shaped into a wire loop. Where will the magnetic field strength be the largest?

Inside the loop

A circular loop of wire has a current flowing through it, as shown. What is the direction of the magnetic field through the center of the loop?

Into the screen

Select all of the following that can happen to unpolarized light when it is scattered.

It can become completely polarized. It can become partially polarized.

As the magnitude of the magnetic field increases, what happens to the radius of the helical magnetic trajectory?

It decreases.

Select all of the following statements that are true regarding the energy density of an electromagnetic wave.

It is directly proportional to the electric field amplitude squared. It is directly proportional to the magnetic field amplitude squared.

Two polarizers are set up so that their axes are at a right angle to each other. A third polarizer is then placed between them with its axis at an angle of 45 degrees with respect to the axes of the other two polarizers. What can be said about the intensity of light passing through all three polarizers?

It is greater than that passing through the two polarizers.

As unpolarized light passes through a polarizer, what happens to its intensity?

It is halved.

Two polarizers are set up so that their axes are aligned with each other. A third polarizer is then placed between them with its axis at an angle of 45 degrees with respect to the axes of the other two polarizers. What can be said about the intensity of light passing through all three polarizers?

It is less than that passing through the two polarizers.

Select all of the following statements that are true regarding the cross product of two vectors.

It is not possible to take the cross product of two scalars. The resultant of the cross product of two vectors is also a vector.

How is the angle θ defined for torque on a current loop?

It is the angle between the magnetic field and a line perpendicular to the plane of the loop.

What is dispersion?

It is the dependence of the speed of a wave on its frequency.

What is infrared radiation?

It is the same as infrared light.

If the magnitude of the magnetic field of an electromagnetic wave is doubled, what will happen to its intensity?

It quadruples.

If the electric field magnitude in an electromagnetic wave were doubled, then what would happen to its energy density?

It would quadruple.

If the magnetic field magnitude in an electromagnetic wave were doubled, what would happen to its energy density?

It would quadruple.

If the radius of a stationary coil doubled, and the magnetic field, current, and number of turns remained constant, then what would happen to the magnitude of the torque on the coil?

It would quadruple.

Which of the following statements is true regarding infrared light?

Its wavelength is greater than those of both visible and ultraviolet light.

Which of the following statements is true regarding ultraviolet light?

Its wavelength is less than those of both visible and infrared light.

To which length is the magnitude of the length vector always equal?

Length of the wire

What does "normal incidence" mean?

Light propagates perpendicularly to a surface.

Six wires, all parallel to each other, carry currents of the same magnitude. Which loop has the largest circulation?

Loop A

Six wires, all parallel to each other, carry currents of the same magnitude. Select the loop that has the largest circulation.

Loop B

Select all of the following statements that are true regarding permanent magnets.

Magnetic field lines enter into their south poles. Magnetic field lines emerge from their north poles.

Select all of the following statements that are true regarding magnetic monopoles.

Magnetic monopoles have not yet been detected. They are either an isolated north pole or an isolated south pole.

Select all of the following that directly produce magnetic fields.

Moving electric charges Changing electric fields

Select all of the following that directly produce electric fields.

Moving electric charges Stationary electric charges Changing magnetic fields

Select all of the following that are equal to T.

N/(A⋅m) (N⋅s)/(C⋅m)

Consider three charged particles moving in a magnetic field. The kinetic energy of which particle increases the most as a result of the work done by the magnetic force?

None of the particles' kinetic energies increases.

An electromagnetic wave in vacuum propagates to the west. If, at a certain time and location, the electric field points upward, what is the direction of the magnetic field at the same time and location?

North

You are given a solenoid and told 1 mA can flow through it. What other properties of the solenoid need to be measured to determine the magnetic field strength it can produce?

Number of turns of the coil Length of the solenoid

Select all of the following on which the magnitude of the magnetic field inside a solenoid depends.

Number of turns of the solenoid Length of the solenoid Current flowing through the solenoid

What will an electron do if it is moving to the right and enters a region where the magnetic field is pointed out of the page?

Orbit in a counterclockwise direction on the page

The current in a long, straight wire remains constant. The magnetic field is measured at point P, 1 m away from the wire. The magnetic field is also measured at point Q, 2 m away from the wire. Which magnetic field will be stronger?

P

Select all of the following that are needed to calculate the speed of an electromagnetic wave in vacuum.

Permeability of vacuum Permittivity of vacuum

Light scattered once through an angle of 90 degrees is polarized in which direction?

Perpendicular both to the direction of the incident light and to the direction of the scattered light

How is light described if its electric field points in only one direction?

Polarized

Which electromagnetic waves have the longest wavelengths?

Radio waves

Which statement is true?

Radio waves are electromagnetic waves.

How is the index of refraction defined?

Ratio of two speeds

Select all of the following statements that are true regarding visible light.

Red has the smallest frequency. Red has the longest wavelength. Violet has the largest frequency. Violet has the shortest wavelength.

What will occur if an object emitting light is moving away from the observer?

Red shift

Select all of the following processes by which polarizers reduce the amount of microwaves transmitted.

Reflection Absorption

Select all of the following that are represented by magnetic field lines.

Relative magnitude of the magnetic field Direction of the magnetic field

A long, straight wire carries a current directed into the screen. Determine the direction of the magnetic field at point R.

Right

An electron and a proton are passed through a velocity selector so that they have the same velocity before entering a region of uniform magnetic field perpendicular to their motions. What is the correct relationship? (Rp and Re are the radii, and Mp and Me are the masses of the proton and the electron, respectively.)

Rp/Re=Mp/Me

Select all of the following EM waves that are not practical for antennas to generate.

Short-wavelength High-frequency

Select all of the following that can be calculated by measuring the Hall effect.

Signs of the moving charges Magnetic field magnitudes Drift velocities of the moving charges

Two solenoids have the same length and the same current flowing through them. Solenoid 1 has a larger magnetic field than solenoid two. Which solenoid has the largest number of turns?

Solenoid 1

To which speed is the speed of an electromagnetic wave in vacuum equal?

Speed of light

Select all of the following that are needed to determine the speed of an electromagnetic wave in matter.

Speed of light in vacuum Index of refraction of the medium

What are the shapes of the trajectories of charged particles in a cyclotron?

Spirals

What are the SI units of magnetic field?

T

Select all statements that are true regarding diamagnetic materials.

The atoms and/or molecules have no permanent dipole moments. The total dipole moment is always zero in the absence of external magnetic fields.

Select all of the following that are reasons why it isn't practical for antennas to generate EM waves with short wavelengths and high frequencies.

The frequency of the ac current is too high. The antenna is too long.

A proton is moving to the north in a uniform magnetic field that is directed to the north. In which direction is the magnetic force on the proton?

The magnetic force has no direction because it is zero.

Diamagnetic materials have magnetic domains that align opposite to an external magnetic field. Once the external magnetic field is removed, what will happen to the magnetization of the material?

The material will no longer be magnetized.

Paramagnetic materials have magnetic domains that align in the presence of an external magnetic field. Once the external magnetic field is removed, what will happen to the magnetization of the material?

The material will no longer be magnetized.

Select all of the following statements that are true regarding magnetic fields and magnetic field lines.

The north pole of a compass needle points along the direction of the magnetic field. Magnetic field lines appear to originate on north poles and terminate on south poles. Magnetic field lines cannot cross each other.

Select all statements that are true regarding paramagnetic materials.

The total dipole moment is always zero in the absence of external magnetic fields. The atoms and/or molecules have permanent dipole moments.

Select all statements that are true regarding ferromagnetic materials.

The total dipole moment may be greater than zero in the absence of external magnetic fields. The atoms and/or molecules have permanent dipole moments.

An electromagnetic wave moves from water into air. The index of refraction of air is approximately 1.00, and the index of refraction of water is approximately 1.50. Select all of the following statements that are true.

The wavelength of the light in water is less than the wavelength of light in air. The speed of the light in water is less than the speed of light in air.

How do the wavelengths of visible light compare to the sizes of atoms?

The wavelengths are much larger.

An electron accelerates along a straight line in the presence of a magnetic field and an electric field. The magnetic and electric forces are the only forces acting on the electron. Which statement is true?

The work done by the magnetic force is zero.

An electron moves with uniform circular motion in the presence of a uniform magnetic field. The magnetic force is the only force acting on the electron. Which statement is true?

The work done by the magnetic force is zero.

A uniform magnetic field points in the +y-direction. A charged particle moves along a helical path in the magnetic field. The magnetic force is the only force acting on the charged particle. Select all statements that are true.

The y-component of the particle's velocity is constant. The magnitude of the particle's velocity is constant.

Which of the following statements is true regarding radio waves?

Their wavelengths are greater than those of both visible and ultraviolet light.

Which of the following statements is true regarding microwaves?

Their wavelengths are greater than those of infrared light and less than those of radio waves.

Which of the following statements is true regarding x-rays and gamma rays?

Their wavelengths are less than those of both visible and ultraviolet light.

Select all of the following statements that are correct regarding the Earth's magnetic field.

There is evidence that Earth's magnetic field has reversed direction in the past. The magnetic north pole is close to geographic South Pole.

When determining the magnitude of the cross product of two vectors, how is the symbol theta defined?

Theta is the angle between the two vectors when they are placed tail to tail.

What are microwaves?

They are a part of the electromagnetic spectrum.

How is a moving charge's velocity and the magnetic field it creates oriented?

They are perpendicular to one another.

A circularly polarized light wave is the superposition of two light waves. How are these two waves polarized?

They are polarized along perpendicular axes.

Select all statements that are true regarding x-rays and gamma rays.

They have the shortest wavelengths of any electromagnetic waves. They are electromagnetic waves.

If electrons move to the right, then what is the direction of the length vector?

To the left

What is the direction of the magnetic force on a straight wire in a uniform magnetic field pointing up toward the sky if the direction of the current is toward you?

To the left

What is the direction of the magnetic force on a straight wire in a uniform magnetic field pointing up toward the sky if the direction of the current is away from you?

To the right

What is the direction of the magnetic force on a straight wire in a uniform magnetic field pointing up toward the sky if the direction of the current is to the right?

Toward you

True or false: The speed of light is the speed at which all electromagnetic waves move through vacuum, not just those waves that are visible to humans.

True

How many quantities are needed to define the index of refraction?

Two

Which electromagnetic waves have wavelengths slightly shorter than visible light?

Ultraviolet rays

How is light described if its electric field points in all directions randomly?

Unpolarized

A long, straight wire carries a current directed out of the page. Determine the direction of the magnetic field at point P.

Up

Which electromagnetic waves have a range of wavelengths from 400 nm to 700 nm?

Visible light

Energy density is the ratio of energy to which of the following quantities?

Volume

Select all of the following that will change as a result of the Doppler effect for electromagnetic waves.

Wavelength Frequency

An electromagnetic wave moves from water into air. The index of refraction of air is approximately 1.00, and the index of refraction of water is approximately 1.50. Select all of the following quantities that change when the light crosses the boundary between the water and the air.

Wavelength Speed

An electromagnetic wave in vacuum propagates to the north. If, at a certain time and location, the magnetic field points upward, what is the direction of the electric field at the same time and location?

West

Which of the following indicates that moving charges create magnetic fields?

When current flows in a circuit, nearby stationary compass needles begin to rotate.

In which of the following situations would an electric dipole antenna be most effective at receiving an electromagnetic wave?

When the antenna and the electric field are parallel

In which of the following situations would a magnetic dipole antenna be most effective at receiving an electromagnetic wave?

When the axis of the antenna and the magnetic field are parallel

The transmission axis of a polarizer is in the y-direction. Unpolarized light incident on this polarizer will emerge polarized in which direction?

y