Chap-2: Waves and Sound Wave is a traveling disturbance. Wave carries energy from place to place. There are two basic types of waves: Transverse and longitudinal waves.

Transverse waves A transverse wave is one in which the disturbance is perpendicular to the direction of travel of the wave. Examples: Light wave, waves on a guitar string.

Longitudinal Waves Longitudinal wave is one in which the disturbance is parallel to the line of travel of the wave. Example: Sound wave in air is a longitudinal wave.

Water Waves Water waves are partly transverse and longitudinal.

Electromagnetic wave Electric and magnetic fields fluctuating together can form a propagating electromagnetic wave.

The Electromagnetic Spectrum

Difference between sound and light Bell-in-Vacuum

Periodic Waves Periodic waves are waves that repeat.

Amplitude, Wavelength, and Period The amplitude, A is the maximum disturbance. The wavelength, λ is the horizontal length of one cycle of the wave. The period, T is the time required for one complete up/down cycle of the wave.

Frequency Frequency is the number of waves per unit time.

Wave Speed

Speed of Sound

2.2 Fundamental Properties of Waves 1.Huygens’s principle 2.Superposition 3.Inverse square law 4.Polarization The above first three phenomena apply to both longitudinal and transverse waves. Polarization is unique to transverse waves, for example light.

WAVE FRONTS AND RAYS The angle between a wave front and a ray is 90 0.

Spherical and plane wave fronts

Wave fronts Circular wave fronts (a) produced by a vibrating ball, and linear wave fronts (b) produced by a vibrating bar in a ripple tank. The lines in both represent the crests of successive waves.

Huygens’s Principle Dutch scientist Christian Huygens (1629–1695) developed a principle that is useful in explaining wave phenomena. Huygens’principle describes how a wave front that exists at one instant gives rise to the wave front that exists later on. This principle states that: Every point on a wave front acts as a source of tiny wavelets that move forward with the same speed as the wave; the wave front at a later instant is the surface that is tangent to the wavelets.

Huygens’s Wavelets

Bending of Sound Waves

The Principle of Linear Superposition When two or more waves are present simultaneously at the same place, the resultant disturbance is the sum of the disturbances from the individual waves. The superposition principle can be used to explain interference of waves.

Constructive Interference of Sound Waves

Destructive Interference

Inverse Square Law

Example on Inverse Square Law

Polarization One of the essential features of electromagnetic waves is that they are transverse waves, and because of this feature they can be polarized. The figure illustrates the idea of polarization by showing a transverse wave as it travels along a rope toward a slit. The wave is said to be plane polarized, which means that its vibrations always occur along one plane. This plane is called the plane of polarization.

The Nature of Electromagnetic Waves The changing magnetic field creates an electric field that fluctuates in time and the changing electric field creates the magnetic field.

POLARIZED ELECTROMAGNETIC WAVES

Polaroid sunglasses When Polaroid sunglasses are uncrossed (left photograph), the transmitted light is dimmed due to the extra thickness of tinted plastic. However, when they are crossed (right photograph), the intensity of the transmitted light is reduced to zero because of the effects of polarization.

Liquid Crystal Displays

THE OCCURRENCE OF POLARIZED LIGHT IN NATURE In the process of being scattered from atmospheric molecules, unpolarized light from the sun becomes polarized.