WAVES AND ONLINE MEDIA…

April 13, 2023

Displacement-time (s-t) graph of Point P

s-d graph s-t graph

(a)

(b)

(d)

(c) (e)

12.3 What are the terms used to describe waves?

Circular water waves

• Water waves are easily produced and observed. By touching one point on the surface, you can see the peaks of the waves form circles and move outwards from the source of disturbance

• The line that joins all the peaks of a wave or all identical points on a wave is called the wavefront

• In the example at the right, the wavefront is circular. The direction of travel of circular waves is perpendicular to the wavefront

12.3 What are the terms used to describe waves?Plane water waves

• Plane waves can be produced by disturbing the water surface with a vibrating wooden bar

• The wavefronts of plane wave are straight lines• The plane waves also travels in a direction

perpendicular to the wavefront

WAVE PRODUCTION AND THE RIPPLE TANK

The bright and dark lines correspond to the crests and troughs of the plane waves respectively.

The depth at which the dipper is placed affects the amplitude of the waves.

The frequency of the waves is determined by the frequency of vibration of the dipper.

A lamp is shone at a shallow glass-bottomed tray of a ripple tank.

Dark and bright lines are formed on a screen by the plane waves.

WAVE PRODUCTION AND THE RIPPLE TANK

Refraction of waves and depth of ripple tank The wavelength of the plane waves shorten as they

travel from deep to shallow water, i.e. λ2<λ1.

The frequency remains unchanged as it is determined by the dipper.

Using v = ƒλ, the speed of waves is slower at the shallow water, i.e. v2<v1

A plastic sheet creates a shallow region of water. Speed and wavelength of waves

decrease from deep to shallow water.

WAVE PRODUCTION AND THE RIPPLE TANK

Similar to light, when waves enter a region of shallow water at an angle, the waves will refract.

If you place a plastic sheet at an angle, the change in speed of the waves will cause them to bend.

WAVE PRODUCTION AND THE RIPPLE TANKReflection of waves A straight barrier standing upright in the water causes

the incoming waves to be reflected.

A straight barrier is placed at an angle to the straight dipper. You can see the waves reflecting at equal angles to the normal in the inset.

HTTP://EN.WIKIPEDIA.ORG/WIKI/WAVE_SHOALING