Module 4 Waves, atoms & Space

Lesson 1 Types of wave

Types of waves Two types of wave Longitudinal Transverse e.g., sound waves Two types of wave Transverse e.g., light, water waves

Longitudinal waves compressions rarefactions Vibrations that we hear as sound travel through the air. The ‘waves’ are caused by air molecules being squashed together or pulled apart. The squashed places are called ‘compressions’. The spaced apart places are called ‘rarefactions’.

Transverse waves Transverse waves move up and down while travelling in the forward direction. Water waves do the same when ripples form on the surface of water. All the waves in the electromagnetic spectrum (e.g., light, radio, gamma etc) are transverse wave.

Measuring waves Longitudinal and transverse waves can be viewed as a wave form using a machine called an oscilloscope. The oscilloscope draws a graph of the wave. You cannot tell from a wave form diagram if the wave is longitudinal or transverse.

The wave form Base line Wavelength (λ)is the distance from one point on the wave form to the same point further up the wave, measured in metres (m) The amplitude (A) is the height of the peak or trough from the base line. The frequency (f) is the number of wavelengths per second. Units for frequency is Hertz (Hz).

Sound When we talk about sound waves, amplitude is the volume or loudness of sound and the frequency is the pitch (how high or low the note is).

Human hearing The human range of hearing is from 20 Hz – 20000 Hz. As you get older your range of hearing gets worse. Bat grasshopper human robin dog cat 0 10000 20000 30000 40000 50000 60000 70000 80000 90000 100000 110000 20

Ultrasound Sound with a frequency greater than 20000 Hz is called ULTRASOUND. We cannot hear ultra sound but animals such as bats use it to locate their prey.

Uses of ultrasound Medical imaging Echo sounding Ultrasound waves are passed through the body. They reflect off the various types of tissues and bones and are detected by the probe. A computer converts the information into an image. Ultrasound is safer than x-rays and shows living tissues rather than just bones. Echo sounding Waves of ultrasound can be used to measure the depth of an ocean floor. The speed of sound travelling through water is known so by timing how long it takes for the ultrasound to travel from and back to the ship will allow you to calculate the depth of the ocean.

Sound travels in water at a speed of 1500 m/s Distance travelled by ultrasound pulse = speed x time Distance Actual depth = 2