Waves

A wave is a series of oscillations (vibrations) that transfer energy from one place to another.

We can categorize waves into two types:

1. Longitudinal waves

2. Transverse waves

Longitudinal Waves

Longitudinal waves are waves with oscillations (vibrations) parallel to the direction of the wave (direction of energy being transferred).

Compression: A region of high pressure, particles are close together

Rarefaction: Region of low pressure, particles are further apart

Examples of longitudinal waves: Sound, ultrasound, seismic P-waves.

The speed of sound in air is 320m/s.

Transverse Waves

Transverse waves are waves where the oscillations (vibrations) are perpendicular (90°) to the direction of the wave (direction of energy being transferred).

Examples of transverse waves: Light, gamma, radio waves.

The speed of light is: 3x10⁸ m/s (300,000,000 meters per second) (this applies to all electromagnetic waves).

All objects have a natural frequency. If this frequency is reached, the objects will increase its amplitude. This is known as resonance.

Visible light is only a small part of the electromagnetic spectrum.

The EM spectrum is continuous. This is evident when looking at a rainbow, as there are no gaps between the colors.

An electromagnetic wave is an oscillation of electric and magnetic fields. It is a transverse wave.

Wave speed = wavelength x frequency

The units for these quantities are as follows:

Wave speed - m/s

Wavelength - m

frequency - Hz

Wavelength and frequency are inversely proportional.

Electromagnetic Spectrum

All electromagnetic waves are transverse, they all travel at 3×10⁸ m/s in a vaccuum.

This (unclear) image shows the electromagnetic spectrum ordered from highest frequency to lowest. It is usually ordered the other way around.

Uses:

• Radio waves → Communication

• Microwaves → Communication - Mobile phones

• Infrared Light → Thermal imaging, remote controls, communication (fiber optic cables)

• Visible light → Communication (fiber optic cables)

  • They carry high rate of data/information

  • Glass is transparent to visible light - (TIR happens)

• Ultraviolet Light → Sterilize surfaces. tanning, analyzing crime scenes, forgery (bank notes)

• X-rays → Scanning bones, security scans (airport baggage)

• Gamma rays → Sterilize surgical equipment, treating cancer (gamma knife)

A common exam question is:

Why are microwaves used for mobile phone signals?

The answer is:

• Microwaves only need short aerials

• Microwaves penetrate walls

Another common question is:

Name some examples of damage caused by x-rays.

The answer would be:

• Mutation

• Cause cancer

• Damage cell tissue

Another one is:

Suggest and explain precautions for the safe use of x-rays

The answer is:

• Use a screen (lead) to absorb radiation.

• Distance from the source, reduce the amount of radiation

• Maximum number of x-rays (to limit the dose)

Communication

Basic Components of a communication system:

Sender → Channel → Receiver

Signals are sent along this path, two types of signals are possible:

• Analogue signals are an example of continuous data with an infinite range of values

Electricity

The components of a circuit

• Battery/Cell - Supplies electrons with energy and pushes electrons around the circuit with what we call electromotor force

• Wire - Transmits electron flow from cell to output

• Resistor - Limits/regulates electron flow

• Bulb - Is the output, will light up if powered

• Variable resistor - A resistor that can change its resistance

In an insulator, electricity will not conduct as the electrons are localized (not free to move)

In a conductor, electricity will conduct as the electrons are delocalized (free to move)

A current is the flow of charge.

In a metal, the electrons are free to move through the object, electrons have a negative charge.

• Charge is measured in coulomb (c)

• The charge of 1 electron is -1.6×10^-19C