AP Physics 2 Quiz: Electromagnetic Waves

What this quiz covers

This quiz focuses on Electromagnetic Waves, giving you a quick way to practice the rules, question types, and explanations that matter most for AP Physics 2.

How to use this quiz

Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

Question 1

1. They travel only in matter because the fields need particles to oscillate.
2. They have electric and magnetic fields parallel to each other so the wave can move forward.
3. They carry charge from the transmitter because an electric field implies moving charge.
4. They consist of oscillating electric and magnetic fields that are perpendicular to each other and to the direction of travel. (correct answer)

Explanation: This question tests understanding of electromagnetic waves. Electromagnetic waves consist of oscillating electric and magnetic fields that are perpendicular to each other and to the direction of wave propagation. The radar pulse shows the electric field pointing upward, the magnetic field pointing to the right, and the pulse moving forward, demonstrating the required perpendicular orientations. These three directions form a right-handed coordinate system characteristic of EM waves. Choice C incorrectly claims that EM waves carry charge, confusing the presence of an electric field with actual charge transport. Remember that EM waves transport energy and momentum but not electric charge through space.

Question 2

1. They require a medium and therefore cannot propagate in a vacuum.
2. They have electric and magnetic fields parallel to each other at every point.
3. They carry net charge because the fields oscillate through space.
4. They have mutually perpendicular electric and magnetic fields, both perpendicular to the direction of travel. (correct answer)

Explanation: This question tests understanding of electromagnetic waves. Electromagnetic waves are characterized by electric and magnetic fields that oscillate perpendicular to each other and to the direction of wave propagation. The problem describes the electric field oscillating vertically and the magnetic field oscillating into/out of the page while the beam travels horizontally, confirming all three directions are mutually perpendicular. This transverse wave nature is fundamental to all electromagnetic radiation. Choice A incorrectly claims EM waves need a medium, confusing them with mechanical waves that require matter for propagation. To identify EM waves, always check that the E and B fields are perpendicular to each other and both are perpendicular to the propagation direction.

Question 3

1. They are longitudinal because both fields oscillate along the direction of travel.
2. They require a medium because the fields must vibrate within matter.
3. They are transverse with perpendicular electric and magnetic fields, each perpendicular to the propagation direction. (correct answer)
4. They transport net charge since electric fields imply moving charges through space.

Explanation: This question tests understanding of electromagnetic waves. Electromagnetic waves are transverse waves with electric and magnetic fields oscillating perpendicular to each other and to the propagation direction. The measurement shows the wave traveling in +z direction with the electric field along +x and magnetic field along +y, confirming all three directions are mutually perpendicular. This transverse nature distinguishes EM waves from longitudinal waves like sound. Choice A incorrectly describes EM waves as longitudinal, misunderstanding that the fields oscillate perpendicular to, not along, the direction of travel. To verify an EM wave, check that E, B, and the propagation direction form a right-handed coordinate system.

Question 4

1. They can have electric and magnetic fields that are parallel if the wave is in a medium.
2. They carry charge through the glass because the fields push electrons forward continuously.
3. They are transverse waves with perpendicular electric and magnetic fields, even while traveling in a medium. (correct answer)
4. They cannot propagate in a vacuum and therefore must always travel in matter.

Explanation: This question tests understanding of electromagnetic waves. Electromagnetic waves maintain their fundamental character as transverse waves with perpendicular electric and magnetic fields even when traveling through a material medium like glass. The electric field oscillates in one transverse direction while the magnetic field oscillates in another transverse direction, both perpendicular to the propagation direction. This perpendicular relationship between E and B fields is a universal property of EM waves regardless of the medium. Choice D incorrectly states that EM waves cannot propagate in vacuum, contradicting the fundamental property that distinguishes them from mechanical waves. Always remember that EM waves can travel through vacuum and maintain their transverse nature in any medium.

Question 5

1. They require air or another medium because fields cannot exist in empty space.
2. They consist of perpendicular oscillating electric and magnetic fields and can travel through empty space. (correct answer)
3. They carry a net flow of charge in the direction of propagation.
4. They have electric and magnetic fields that are always parallel to each other.

Explanation: This question tests understanding of electromagnetic waves. Electromagnetic waves consist of oscillating electric and magnetic fields that are perpendicular to each other and to the direction of propagation. The visible light wave shows the electric field oscillating north-south, the magnetic field oscillating east-west, and both perpendicular to the travel direction toward the astronaut. These waves can propagate through the vacuum of space without any material medium. Choice A incorrectly claims that fields cannot exist in empty space, reflecting a misconception that confuses electromagnetic waves with mechanical waves. Remember that EM waves can travel through vacuum because the oscillating fields sustain each other through electromagnetic induction.

Question 6

1. They consist of oscillating electric and magnetic fields perpendicular to each other and to the direction of travel. (correct answer)
2. They consist of electric and magnetic fields that are parallel to each other as the wave travels.
3. They require a material medium to propagate and cannot travel through vacuum.
4. They propagate by transporting net electric charge from the source to the detector.

Explanation: This question tests understanding of electromagnetic waves. Electromagnetic waves consist of oscillating electric and magnetic fields that are perpendicular to each other and to the direction of wave propagation. In this problem, the electric field oscillates along +y, the magnetic field along +z, so the wave must travel along +x (or -x), with all three directions mutually perpendicular. The wave travels through vacuum, demonstrating that EM waves do not require a material medium for propagation. Choice A incorrectly states that EM waves need a medium, reflecting the misconception that all waves behave like mechanical waves. Remember that electromagnetic waves are self-sustaining oscillations of electric and magnetic fields that can propagate through empty space.

Question 7

1. one-fourth as large because intensity spreads over a larger spherical area. (correct answer)
2. one-half as large because frequency decreases with distance traveled.
3. twice as large because the fields add constructively in vacuum.
4. unchanged because electromagnetic waves do not spread out in space.

Explanation: This question tests understanding of electromagnetic waves. Electromagnetic waves consist of oscillating electric and magnetic fields that are perpendicular to each other and to the direction of propagation. For a point source emitting uniformly in all directions, the intensity follows an inverse square law: intensity is proportional to 1/r². When the distance doubles from r to 2r, the intensity becomes 1/(2r)² = 1/4r², which is one-fourth the original intensity. Choice B incorrectly claims frequency changes with distance, confusing the Doppler effect with intensity spreading. The key principle is that electromagnetic wave intensity from a point source decreases as 1/r² due to energy spreading over larger spherical surfaces.

Question 8

1. Its frequency decreases because electromagnetic waves slow down by losing charge.
2. Its polarization changes because the electric and magnetic fields become parallel.
3. Its wavelength increases because $\lambda=vf$ and $v$ decreases.
4. Its wavelength decreases because $\lambda=v/f$ and $v$ decreases. (correct answer)

Explanation: This question tests understanding of electromagnetic waves. Electromagnetic waves consist of oscillating electric and magnetic fields perpendicular to each other and to the direction of propagation. When an EM wave enters a medium where its speed decreases, the frequency remains constant (determined by the source), but wavelength must decrease according to λ = v/f. Since v decreases and f is constant, λ decreases proportionally. Choice C incorrectly claims frequency changes, misunderstanding that frequency is a source property that doesn't change when crossing boundaries. Remember that when electromagnetic waves enter a denser medium, speed and wavelength decrease together while frequency remains constant.

Question 9

1. a larger wavelength and a larger speed.
2. a larger wavelength and a smaller speed.
3. a smaller wavelength and a larger speed.
4. a smaller wavelength and a smaller speed. (correct answer)

Explanation: This question tests understanding of electromagnetic waves. Electromagnetic waves consist of oscillating electric and magnetic fields perpendicular to each other and to the direction of propagation. When an EM wave enters a denser medium like glass, its speed decreases while its frequency remains constant (frequency is determined by the source). Since v = fλ, and v decreases while f stays constant, the wavelength λ must decrease proportionally. Choice B incorrectly suggests wavelength increases, reflecting confusion about the wave equation relationship. Remember that when electromagnetic waves enter a denser medium, they slow down and their wavelength decreases, but frequency always remains unchanged.

Question 10

1. Its electric and magnetic fields are perpendicular to each other and to the direction of travel. (correct answer)
2. It carries a net flow of electric charge in the propagation direction.
3. Its electric and magnetic fields must be parallel for energy to be transported.
4. It requires air molecules so the oscillations can be passed from particle to particle.

Explanation: This question tests understanding of electromagnetic waves. Electromagnetic waves consist of electric and magnetic fields that oscillate perpendicular to each other and perpendicular to the direction of propagation. With the electric field along +x and magnetic field along +y, both are perpendicular to each other and must be perpendicular to the propagation direction (which would be along ±z). Choice A incorrectly suggests electromagnetic waves need air molecules to propagate, reflecting the misconception that all waves require a material medium like sound waves. Electromagnetic waves are self-sustaining disturbances in the electromagnetic field that can travel through vacuum. Remember that electromagnetic waves always have mutually perpendicular electric and magnetic fields that are transverse to the propagation direction.

Question 11

1. They cannot travel in vacuum because they must compress and rarefy a medium.
2. They have perpendicular electric and magnetic fields and do not require a medium. (correct answer)
3. They transport net charge because the electric field produces a current in space.
4. They have electric and magnetic fields that are parallel to each other as they travel.

Explanation: This question tests understanding of electromagnetic waves. Electromagnetic waves consist of electric and magnetic fields that oscillate perpendicular to each other and perpendicular to the direction of propagation. The infrared wave has its electric field oscillating in one direction perpendicular to travel and its magnetic field in a second perpendicular direction, which correctly describes the transverse nature of electromagnetic waves. Choice A incorrectly assumes electromagnetic waves compress and rarefy a medium, confusing them with longitudinal mechanical waves like sound. Electromagnetic waves are self-propagating disturbances that require no material medium because the oscillating fields sustain each other. Remember that all electromagnetic waves can travel through vacuum with perpendicular E and B fields.

Question 12

1. They require a medium because only matter can support transverse oscillations.
2. They are composed of perpendicular electric and magnetic fields and can propagate without a medium. (correct answer)
3. They carry a net current because changing magnetic fields move charges forward.
4. They have electric and magnetic fields that point in the same direction at each instant.

Explanation: This question tests understanding of electromagnetic waves. Electromagnetic waves are composed of perpendicular electric and magnetic fields that oscillate transverse to the propagation direction and can propagate without any material medium. The plane wave demonstrates this with vertical electric field oscillations and horizontal magnetic field oscillations, both transverse to propagation. The self-sustaining nature of these fields allows EM waves to travel through vacuum. Choice A incorrectly states that only matter can support transverse oscillations, failing to recognize that electromagnetic fields can oscillate in vacuum. Always remember that EM waves can travel through vacuum because the changing fields induce each other.

Question 13

1. In the $+x$ direction.
2. In the $+z$ direction.
3. In no direction, because a medium is required for $B$ to oscillate.
4. In the $+y$ direction. (correct answer)

Explanation: This question tests understanding of electromagnetic waves. Electromagnetic waves consist of oscillating electric and magnetic fields that are perpendicular to each other and to the direction of propagation. With the wave traveling in +z and the electric field oscillating in +x, the magnetic field must oscillate in a direction perpendicular to both, which is the +y direction (using the right-hand rule: E × B points in the direction of propagation). The three directions form a right-handed coordinate system. Choice D incorrectly suggests that a medium is required for the magnetic field to oscillate, confusing EM waves with mechanical waves. Remember to use the right-hand rule: point fingers along E, curl toward B, and thumb points in the propagation direction.

Question 14

1. The wave's frequency. (correct answer)
2. The wave's speed.
3. The wave's wavelength.
4. The wave's net charge per unit length.

Explanation: This question tests understanding of electromagnetic waves. Electromagnetic waves maintain their frequency when crossing boundaries between media, while their speed and wavelength change according to the refractive index. The perpendicular relationship between E and B fields is preserved in all media, but this is a property of the wave structure, not a boundary condition. Choice C incorrectly suggests wavelength stays constant—this misconception confuses frequency (which is constant) with wavelength (which changes). Remember that frequency is determined by the source and remains constant across boundaries.

Question 15

1. It can propagate through a vacuum because it does not require a material medium. (correct answer)
2. It requires a medium because electromagnetic waves are vibrations of matter.
3. Its electric and magnetic fields are parallel to each other as it travels.
4. It transports net electric charge in the direction of propagation.

Explanation: This question tests understanding of electromagnetic waves. Electromagnetic waves consist of oscillating electric and magnetic fields that are perpendicular to each other and to the direction of propagation. In this case, with the electric field in the +y direction and magnetic field in the +z direction, the wave must propagate in the +x direction (or -x), forming a self-sustaining wave that requires no material medium. Choice B incorrectly assumes electromagnetic waves need matter to propagate, reflecting the misconception that all waves are mechanical. Unlike sound waves, electromagnetic waves can travel through the vacuum of space because the changing electric field creates a changing magnetic field and vice versa. Remember that electromagnetic waves are transverse waves that can propagate through vacuum, distinguishing them from mechanical waves.

Question 16

1. Its electric and magnetic fields are perpendicular to each other and to the propagation direction. (correct answer)
2. It requires a medium because electromagnetic waves are mechanical disturbances.
3. Its electric and magnetic fields are parallel, oscillating in the same direction.
4. It carries net charge because the electric field points away from charges.

Explanation: This question tests understanding of electromagnetic waves. Electromagnetic waves are composed of electric and magnetic fields that oscillate perpendicular to each other and perpendicular to the direction of propagation. The laser beam's electric field oscillates in one transverse direction while the magnetic field oscillates in a different transverse direction, both perpendicular to the beam's travel direction. Choice A incorrectly claims electromagnetic waves are mechanical disturbances requiring a medium, which is a common misconception confusing electromagnetic waves with sound or water waves. Electromagnetic waves are self-propagating disturbances in the electromagnetic field that can travel through vacuum. To identify electromagnetic waves, verify that the electric and magnetic fields are mutually perpendicular and transverse to propagation.

Question 17

1. They consist of mutually perpendicular electric and magnetic fields transverse to propagation. (correct answer)
2. They transport net charge because the magnetic field causes charges to drift forward.
3. They cannot propagate in vacuum because fields need a material medium.
4. They have electric and magnetic fields that are parallel to the direction of travel.

Explanation: This question tests understanding of electromagnetic waves. Electromagnetic waves are characterized by electric and magnetic fields that oscillate perpendicular to each other and perpendicular to the direction of propagation. In this example, the wave travels in +x, the electric field oscillates in +z, and the magnetic field oscillates in +y, demonstrating the three mutually perpendicular directions. Choice A incorrectly assumes electromagnetic waves need a material medium, confusing them with mechanical waves that do require matter for propagation. Electromagnetic waves are self-propagating disturbances that can travel through vacuum because the changing fields sustain each other. To verify an electromagnetic wave, confirm that E, B, and the propagation direction form three mutually perpendicular axes.

Question 18

1. They require a medium because the magnetic field must be produced by nearby moving charges.
2. They carry net electric charge because the electric field oscillates.
3. They have electric and magnetic fields that remain parallel to maintain constant speed.
4. They have electric and magnetic fields perpendicular to each other and can propagate in vacuum. (correct answer)

Explanation: This question tests understanding of electromagnetic waves. Electromagnetic waves consist of oscillating electric and magnetic fields that are perpendicular to each other and perpendicular to the direction of wave propagation. The X-ray pulse described has its electric field along +y and magnetic field along +z, which are perpendicular to each other and would propagate along ±x direction. Choice A reflects the misconception that electromagnetic waves require moving charges in a medium to propagate, but electromagnetic waves are self-sustaining and can travel through vacuum. The changing electric field induces a changing magnetic field and vice versa, allowing propagation without any material medium. Remember that all electromagnetic waves, from radio to gamma rays, share this perpendicular field configuration and vacuum propagation ability.

Question 19

1. They require a medium because the oscillations must be carried by particles.
2. They have electric and magnetic fields that are perpendicular to each other and transverse. (correct answer)
3. They carry net charge because the electric field alternates direction.
4. They have electric and magnetic fields that remain parallel during propagation.

Explanation: This question tests understanding of electromagnetic waves. Electromagnetic waves are characterized by electric and magnetic fields that oscillate perpendicular to each other and perpendicular to the direction of propagation. The electric field pointing in +y and magnetic field in +z are perpendicular to each other, and both reverse direction periodically as they oscillate, which is typical electromagnetic wave behavior. Choice A reflects the misconception that electromagnetic waves need particles to carry oscillations, confusing them with mechanical waves like sound. Electromagnetic waves propagate through vacuum because the changing fields sustain each other without requiring any material medium. To recognize electromagnetic waves, confirm that E and B fields are perpendicular to each other and transverse to propagation.

Question 20

1. They require a medium because the fields must be supported by moving charges.
2. They consist of perpendicular electric and magnetic fields and can travel in vacuum. (correct answer)
3. They carry net charge because the electric field points in the direction of travel.
4. They have electric and magnetic fields that are always parallel to each other.

Explanation: This question tests understanding of electromagnetic waves. Electromagnetic waves are composed of electric and magnetic fields that oscillate perpendicular to each other and perpendicular to the direction of wave propagation. The vertical electric field and horizontal magnetic field described are indeed perpendicular to each other and to the propagation direction, which is a fundamental characteristic of electromagnetic waves. Choice A reflects the common misconception that electromagnetic waves require a medium like mechanical waves do, but electromagnetic waves can propagate through vacuum. The self-sustaining nature of electromagnetic waves allows them to travel through empty space without any material medium. To identify electromagnetic waves, always check that the electric and magnetic fields are perpendicular to each other and transverse to the direction of propagation.