MCAT Physical : Longitudinal and Transverse Waves

Study concepts, example questions & explanations for MCAT Physical

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Example Questions

Example Question #1 : Longitudinal And Transverse Waves

At a local concert, a speaker is set up to produce low-pitched base sounds with a frequency range of 20Hz to 200Hz, which can be modeled as  sine waves. In a simplified model, the sound waves the speaker produces can be modeled as a cylindrical pipe with one end closed that travel through the air at a velocity of , where T is the temperature in °C.

What type of waves are sound waves?

Possible Answers:

Longitudinal

Gravitational

Transverse

Electromagnetic

Correct answer:

Longitudinal

Explanation:

Sound waves are longitudinal waves, meaning that the waves propagate by compression and rarefaction of their medium. They are termed longitudinal waves because the particles in the medium through which the wave travels (air molecules in our case) oscillate parallel to the direction of motion. Alternatively, transverse waves oscillate perpendicular to the direction of motion. Common examples of transverse waves include light and, to a basic approximation, waves on the ocean.

Example Question #51 : Waves

Which of these is an example of a longitudinal wave?

Possible Answers:

Microwaves

A sound wave

X-rays

Visible light

A wave produced by a rope oscillating in a plane

Correct answer:

A sound wave

Explanation:

Longitudinal waves transmit energy by compressing and rarefacting the medium in the same direction as they are traveling. Sounds waves are longitudinal waves and travel by compressing the air through which they travel, causing vibration.

Light, X-rays, and microwaves are all examples of electromagnetic waves; even if you cannot recall if they are longitudinal or transverse, they are all members of the same phenomenon and will have the same type of wave transmission. Transverse waves are generated by oscillation within a plane perpendicular to the direction of motion. Oscillating a rope is a transverse wave, as it is not compressing in the direction of motion.

Example Question #3 : Longitudinal And Transverse Waves

Which of the following is a standing wave?

Possible Answers:

Ocean waves hitting a pier every ten seconds

A vibrating violin string

Light with a wavelength of exactly

A bus rumbling over a metal bridge

The sound made by an electric fan

Correct answer:

A vibrating violin string

Explanation:

A simple definition of a standing wave is a wave that is self-reinforcing, which is to say that reflection of the wave through the medium results in some areas of amplification (anti-nodes) of the wave and some areas of nullification (nodes). In other words, resonance must occur, and that usually suggests confinement of the wave in some fashion.

A fan and a bus make noise and vibration, but the sound does not resonate. It is transmitted, but not confined. Light with a specific wavelength has no "resonant" character, and neither do waves striking a pier. If the waves were confined in a harbor so that they could amplify, it might be possible to produce a standing wave. Microwaves trapped inside a microwave oven have this feature, producing antinodes of intense heating and nodes where no energy is transmitted into the food; this is the reason that microwave ovens have rotating platforms to make heating of the food item more uniform.

A violin string will be seen to have discrete, stable regions of motion and lack of motion, the requirements of the standing wave phenomenon. The points of reflection on the string are the two ends. The vibration of the wave is confined within the string, amplifying the sound as the nodes overlap.

Example Question #1 : Longitudinal And Transverse Waves

All of the following are transverse waves, except __________.

Possible Answers:

microwaves

sound waves

light waves

X-rays

Correct answer:

sound waves

Explanation:

An important distinction for the MCAT is the difference between transverse and longitudinal waves. Although both wave types are sinusoidal, transverse waves oscillate perpendicular to the direction of propagation, while longitudinal waves oscillate parallel to the direction of propagation.

The most common transverse and longitudinal waves are light waves and sound waves, respectively. All electromagnetic waves (light waves, microwaves, X-rays, radio waves) are transverse. All sound waves are longitudinal.

Example Question #2 : Longitudinal And Transverse Waves

What phenomenon can occur with light, but not sound?

Possible Answers:

Interference

Doppler effect

Polarization

All of these could occur with both light and sound

Refraction

Correct answer:

Polarization

Explanation:

Sound is a longitudinal wave, while light is a transverse wave. Polarization requires the direction of the wave to be perpendicular to the direction of propogation; only light can do this. Doppler effect, refraction, and interference occur in both wave types.

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