Properties Of Waves

PROPERTIES OF WAVES

All waves exhibit the following properties

• Reflection
• Refraction
• Diffraction
• Interference

Apart from the properties listed above transverse waves has another properties called polarization.

Reflection

This is a property of wave which occurs when a travelling wave strikes a surface and it bounces back. The travelling wave is the incident wave while the one that bounces back is the reflected rain. In case of water waves generated in a ripple tank, if the waves were made to incident normally on a plane strip, the wave will be reflected back along their original course.

If the waves are incident at a particular angle, it will be observed that the angle of incidence is equal to the angle of reflection in line with the laws of reflection

LAWS OF REFLECTION

• The incident ray, the reflected ray and the normal, at point of incidence, all lie on the same plane.
• The angle of incidences is equal to the angle of reflection

Refraction

This is the change in the speed and direction of waves as it passes from one medium to another.

When plane waves pass from deep to shallow water, their wavelength becomes shorter and thereby travels slowly.  A change in the wavelength and speed produce a change in the direction of travel of waves when they cross the boundary.  It is important to note that during refraction, the wavelength remains constant.

Refractive index is the ratio of the sine of the incident angle (i) to the sine of the angle of refraction (r). It is also the ratio of the velocity of the wave in the first medium (v₁) to the velocity in the second medium (v₂)

Diffraction

This is the spreading out of a wave on passing through a narrow opening.

If waves are directed towards a large gap compared with the wavelength of the waves, slightly bent or beam of waves are formed on passing through the gap.

If the barriers are placed closer to leave a narrow gap waves forms spherical wave fronts on passing through a narrow shit.

Diffraction occurs when the wavelength of the wave is longer than the width of the opening or the size of the obstacles.

Interference

This is a phenomenon which occurs when two similar waves traveling in the same direction cross each other. If the waves are in phase or step so that they travel the same distance at equal time and the crest or trough of the two waves arrive simultaneously or one is a complete wavelength ahead of the other.  The resulting wave will build up to twice the amplitude of the two waves; this is called constructive or additive interference.

If the crest of one wave arrives with the troughs of the waves, and vice-versa, the waves cancel each other out to give zero resultant, this is called destructive interference.

Polarization

This is an exclusive property of transverse waves only. It is the production of transverse vibration in only one plane. A transverse wave which vibrates in only one plane is said to be plane-polarized.

Polarized light can be produced by passing an ordinary light through a polarizer called Polaroid or crystal of calcite, tourmaline or quartz.  The arrangement of molecules within this polarizer will only permit the passage of light in a particular plane and then absorb light due to other vibration.  Thus, when an unpolarized light is passed through a polarizer, the emergent light consists in only one plane.

Application of Polaroid

The Polaroid is used in sunglasses to reduce the intensity of incident light and to eliminate reflected light glare.

CLASSWORK 9

1. (a) List the properties of waves that you know

(b) Explain any two

• Define and explain the types of interference

ASSIGNMENT 9

SECTTION A

1. When a wave travels from air to water medium (a) the speed reduces (b) the speed increases (c) reflection occurs (d) all of the above (e) none of the above
2. The phenomenon which occurs when two similar waves traveling in the same direction cross each other  (a) reflection (b) diffraction (c) refraction (d) polarization (e) interference
3. Water waves are generated by dropping a stone into a calm pool of water. If a small piece of cork is floating in the path of the waves, the cork, as the wave progresses, will (a) sink into the water (b) move up and down about the same position (c) move toward the center of the pool (d) move along with the waves toward the bank of the pool (e) none of the above
4. Surface waves travelling in deep water at 15ms^-1 are incident at a shallow water boundary. If the angles of incidence and refraction are 45⁰and 30⁰ respectively, calculate the speed of the waves in the shallow water (a) 8.1 ms^-1 (b) 10.0 ms^-1 (c) 10.6 ms^-1 (d) 22.5 ms^-1 (e) 15ms^-1
5. Which of the following is an exclusive property of transverse waves only (a) reflection (b) diffraction (c) refraction (d) polarization (e) interference

SECTION B

1. What is polarization? State three uses of a Polaroid
2. Differentiate between reflection and refraction