Wave Physics and the Electromagnetic Spectrum

Comprehensive practice questions covering types of waves, their properties, the electromagnetic spectrum, and the specific uses and dangers of various radiation types.

What is the definition of a wave?

A wave is a disturbance or vibration that transfers energy from one place to another without transferring the medium itself.

What is a transverse wave?

A wave in which the vibrations of the particles are perpendicular to the direction of wave travel.

What are the common features of a transverse wave?

Particles move up and down, and the wave has crests and troughs.

List three examples of transverse waves.

Water waves, light waves (electromagnetic waves), and waves on a string.

What is a longitudinal wave?

A wave in which the vibrations of the particles are parallel to the direction of wave travel.

What are the common features of a longitudinal wave?

Particles vibrate back and forth, and the wave has compressions and rarefactions.

List two examples of longitudinal waves.

Sound waves and Seismic P-waves (created during an earthquake).

Can longitudinal waves travel through a vacuum?

No; for instance, sound waves cannot travel in a vacuum.

What is defined as the maximum displacement of a point on the wave from its rest position?

Amplitude ($A$).

What is the relationship between amplitude and energy?

Amplitude indicates the energy carried by the wave; greater amplitude results in more energy (e.g., a louder noise).

How is wavelength ($\lambda$) defined?

The distance between two successive points on a wave that are in the same phase, such as crest to crest or compression to compression.

What is the frequency ($f$) of a wave and what is its unit?

The number of complete waves (oscillations) passing a point each second, measured in hertz ($Hz$).

What is the formula for frequency ($f$) in relation to the time period ($T$)?

$$f = \frac{1}{T}$$

What is the time period ($T$) of a wave?

The time taken for one complete wave (oscillation), measured in seconds ($s$).

What is a wavefront?

A line or surface joining points on a wave that are in the same phase of vibration.

State the wave speed formula.

$v = f\times\text{λ}$ where $v$ is speed ($m/s$), $f$ is frequency ($Hz$), and $\text{λ}$ is wavelength ($m$).

What speed do all electromagnetic (EM) waves travel at in a vacuum?

$3 \times 10^8\text{ }m/s$ (the speed of light).

List the electromagnetic spectrum in order of increasing frequency (and decreasing wavelength).

Radio waves, Microwaves, Infrared, Visible light, Ultraviolet, X-ray, and Gamma Ray.

What are the common properties shared by all electromagnetic waves?

They travel as transverse waves, travel at the speed of light in a vacuum, transfer energy, and can be reflected and refracted.

How do microwaves cook food?

Water molecules inside the food absorb the microwaves and heat up rapidly, cooking the food throughout.

What is the mechanism by which light signals travel inside optical fibers?

Total internal reflection.

How does fluorescence occur in fluorescent tubes?

Electric currents pass through mercury vapor emitting UV rays, which strike the internal coating of the tube, causing it to glow and emit visible light.

Why are X-rays used for imaging bones?

X-rays penetrate soft body tissues (muscles, skin) but are absorbed by dense materials like bone, casting a shadow image.

What is the use of radiotherapy involving gamma rays?

High doses of targeted gamma rays intersect at a tumor site to kill cancer cells while minimizing damage to healthy tissue.

What health risk is associated with overexposure to microwaves?

Internal heating of body tissue because water molecules absorb energy.

What danger is posed by excessive exposure to ultraviolet (UV) radiation?

It can cause sunburn, skin cancer, and blindness.

How are X-rays and Gamma rays stored or shielded?

They are stored in lead boxes, and workers use lead-shielded screens or protective lead aprons.

List the colors of visible light in order of decreasing wavelength.

Red, Orange, Yellow, Green, Blue, Indigo, Violet.

Which color of visible light has the highest frequency?

Violet light (it has the shortest wavelength and highest frequency).

If a gamma ray has a wavelength of $8.0 \times 10^{-13}\text{ }m$, how would you calculate its frequency?

Using $f = \frac{v}{\text{λ}}$, where $v = 3 \times 10^8\text{ }m/s$, giving $f = \frac{3 \times 10^8}{8.0 \times 10^{-13}} = 3.75 \times 10^{20}\text{ }Hz$.