Wave Interaction

Grade 7 Science Worksheets

How are waves created?

Waves are the disturbances or vibrations that are caused in a media. It is constantly being created and always traveling through different media.

Some waves need a medium (matter) to travel through and some waves can travel in empty space or vacuum.

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Mechanical waves

Mechanical waves are those waves which when travels transfers energy on the medium traveled.

That is the energy is transferred from one particle to another. If there was no particle, there would be no energy transfer.

Electromagnetic waves

Waves that travel without the help of a medium are called electromagnetic waves.

Electromagnetic waves even travel in vacuum; they do not necessarily need a medium.

What are the different types of waves?

There are 3 types of mechanical waves:

Transverse waves,
Longitudinal waves,
Surface waves.

Transverse Waves

Waves which have a tendency to travel perpendicular to an applied force are Transverse waves. Transverse begins with the letter “T”. It looks like a perpendicular. Hence this is easy to understand.

Transverse wave can be created by tying a rope to a nail on the wall or tying one end to a tree and moving the rope up and down. We would find that the wave direction is perpendicular to our action. The wave moves towards the tree.

Credit: http://philschatz.com/physics-book/contents/m42248.html

The highest part of a transverse wave is called crest and the lowest point is called trough.

Here AB is the force applied and BC is the wave direction.

Therefore, the wave travels perpendicular to the force we apply. Radio waves and light waves are transverse in nature.

Longitudinal Waves

Longitudinal mechanical waves are waves that travel parallel to the applied force.

A longitudinal wave can be experimented with the help of a spring slinky by you and one other person. The other end can be held still while you hit your end.

You will see that the coils of the spring move close together and also far apart at the same time. Therefore we say that the longitudinal wave travels parallel to the force applied.

Sound waves are longitudinal waves too.

Surface Waves

When certain waves travel along two different mediums, such as air and water or

liquids of different densities is called as surface waves.

When wind blows over. It causes wave called surface wave. These waves are totally different as compared to the other waves as it moves in circular motion.

We notice ripples on water and also see large gigantic waves capable of sinking large ships. These all are surface waves. One of the examples of surface waves is the tsunami which happens because of undersea earthquakes, or shift of tectonic plates. These waves can hardly be observed in the middle of the ocean, but as they reach the shore, they are in giant sizes. Some are even reaching 200 feet in height.

Credit: https://commons.wikimedia.org/wiki/File:Waves_in_pacifica_1.jpg

Electromagnetic waves

Waves which travel without the help of a medium is said to be electromagnetic waves. They can travel in vacuum or empty space.

For example light, sunrays, another example is wifi routers- these send electromagnetic waves.

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Check Point

A. Fill in the blanks –

Waves are disturbances that cause………….. to vibrate.
Waves that travel by transferring their energy in matter are called…………………waves.
Waves that do not need a medium to travel are called ……………. waves.
…………………… mechanical waves are waves that travel perpendicular to an applied force.
Longitudinal waves are mechanical waves that travel ………….. to an applied force.

B. State True or False –

Electromagnetic waves can travel in empty space or space that has no particles.
Transverse mechanical waves are waves that travel parallel to an applied force.
Longitudinal waves are the same as Transverse waves.
Surface waves are waves that travel along the boundary between two different media, such as air and water or liquids of different densities.
Tsunamis are huge longitudinal waves caused by shift of tectonic plates.

Answer Key

A. Fill in the blanks –

Media
Mechanical
Electromagnetic
Transverse
Parallel

B. State True or False –

True
False
False
True
False

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