### GCSE Physics Revision: Waves for Detection & Exploration

#### 5th April 2017

GCSE Science – GCSE Physics – Waves

KEY STAGE 4 – GCSE Physics Revision Guide – Waves for Detection and Exploration

Then use this Revision Guide to remember all the Key Points in the GCSE Syllabus and get Full Marks in your GCSE Physics Exam.

What is a wave?

‘Mechanical Waves’ can be described as:

• a disturbance which travels through a medium (solid, liquid or gas) or

• an oscillation in the particles of a particular medium which travels in a particular direction.

Examples of ‘waves’:

• sound waves

• pressure waves

• seismic waves (i.e. from earthquakes, explosions)

• light waves

Different types of mechanical wave?

• Longitudinal Waves:  displacement (of particles) is parallel to the direction of the wave

NOTE:  Longitudinal waves cannot travel through a vacuum!

Examples of Longitudinal Waves

• Sound waves

• Primary (faster) waves in earthquakes or explosions (can pass through solid and liquid mediums)

• Transverse Waves:  displacement of particles is perpendicular to the direction of the wave

NOTE:  Transverse waves like light and electromagnetic waves can travel through a vacuum without slowing down!

Examples of Transverse Waves

• Light waves

• Secondary (slower) waves in earthquakes or explosions (can only pass through a solid medium)

How can we use waves?

Remember: Animals like dolphins and bats use sound waves in a process called “echo-location”, to find their way around or find their food in the dark.

We can do the same:

Example of how we use sound waves and “sonar”:

Using ultrasonic waves above 20,000 Hertz or 20 ‘Kilohertz’ (above human audible range), we can measure distances between two materials of different densities.

• A detector is placed close to the source of the waves

• Waves are emitted from the source

• Some of the waves will be ‘reflected’ back and ‘detected’

• The time it took for the waves to ‘bounce’ back and be detected can be used to calculate the distance of the change in density/material

• Calculate the distance: Multiply the speed of the wave/s by the time it took to bounce back!

Where is ‘echo-location’ or ‘sonar’ used by humans?

In ships and submarines to:

• to find out the depth of the water

• to look at the sea bed

• to look for shoals of fish

• to look for other submarines and ships.

As described above, in the same way as dolphins, pulses of sound waves are sent, bounce/reflect off an object (seabed, rock, or shoal of fish) and is detected upon their return.

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