Waves and EM Spectrum unit slides 2024-2025

Wave

A wave is a vibration that transfers energy from one place to another

Mechanical waves

Waves that require a medium to travel through, such as sound waves.

Electromagnetic waves

Waves that do not require a medium and can travel through a vacuum, such as light waves.

Longitudinal waves

Waves in which the vibrations are parallel to the direction the wave travels.

Transverse waves

Waves in which the vibrations are perpendicular to the direction the wave travels.

Frequency

The number of waves that pass a given point in a second.

Wavelength

The distance between two consecutive points of the same phase in a wave.

Reflection

Reflection involves a change in direction of waves when they bounce off a barrier. EX. ECHO

What is the law of reflection?

The law of reflection states that the angle of reflection equals the angle of incidence— θ_r = θ_i.

Does wavelength and frequency change when waves are reflected?

No!

Refraction

The bending of waves as they pass from one medium to another due to a change in speed.

Diffraction

The spreading out of waves when they pass through a gap or around obstacles.

The greater the wavelength, the ——- the diffraction

Greater

Transmission

Transmission occurs when waves pass through a given point or medium

Absorbtion

Absorption occurs when waves arrive at the boundary between two materials and their energy is absorbed. I.e., sunlight energy absorbed by your skin

Scattering

Scattering occurs when waves are diffused in all directions

Electromagnetic spectrum

The range of all types of electromagnetic waves that are arranged by wavelength.

Are waves in the EM spectrum transversal or longitudinal?

Transversal.

Do EM waves need a medium?

No, they travel through a vacuum (without a medium) at the speed of light, which is approximately 300,000,000 m/s.

What does it mean when waves are inversly related?

It means when something goes up, the other goes down. This applies to frequency and wavelength.

The higher the frequency, the greater its ——

energy

What are all the EM waves?

Radio, microwave, infrared, visible light, ultra-violet, X-ray, gamma ray.

Which wave has the highest frequency and the shortest wavelength?

Gamma rays

Which wave has the lowest frequency and the longest wavelength?

Radio waves

What mnemonic device is used to remember the order of wavelengths of visible light?

ROYGBIV (Red, Orange, Yellow, Green, Blue, Indigo, Violet)

Dispersion

Light is refracted when passing through glass; this is because different colors travel at different speeds.

Radio waves

Used for radio and television communications. They have a long wavelength and are relflected by an ionosphere.

Microwaves

Used for satellite communication (ionosphere) and for heating food in a microwave.

Infrared Waves

Used in remote controls and infrared cameras (allows you to take pictures in the night using thermography)

Visible light waves

Used in fibre optics and allows you to see colors. The only wave you can see!

Ultra-violet waves

Used to tan, kills bacteria, can cause skin cancer.

X-rays

Used in medical imaging and in security purposes (airports). X-rays can cause mutations and cancer.

Gamma rays

Used for cleaning bacteria off of medical treatment.

What is the formula for velocity?

V= = frequency x wavelength or wavelength/wave period

What units are used for velocity?

m/s - meters per second

What formula is used for wavelength?

W = velocity/frequency

What units are used for wavelength?

m - meters

What formula is used for wave period?

T = 1/frequency or wavelength/velocity

What units are used for wave period?

s - seconds

What is a wavelength?

The distance/length from one point of the wave to the next successive point.

What is wave period?

Time it takes for two successive wave crests to pass a point.

What is the formula for frequency?

f = velocity/wavelength or 1/wave period

What units are used for frequency?

Hz - Hertz

crest/peak

The highest point of a wave/top of the wave.

Trough

Lowest point/part of a wave.

Wave direction

The direction the wave is traveling

Amplitude

The height of the peak, or the depth of the trough from the middle.

Rarefaction

Where particles are furthest apart in a longitudinal wave, where the wave has the lowest density.

Compression

Where particles are closest together in a longitudinal wave, where the wave has the highest density.

Oscillation

An oscillation in a wave refers to the repeated back-and-forth or up-and-down motion of individual particles or points in a medium (or field) as a wave passes through them.