4 Oscillations ans Waves (10 h)

Transcription

1 4 Oscillations ans Waves (10 h) Kari Eloranta 2015 Jyväskylän Lyseon lukio International Baccalaureate November 30, 2015

2 4.4 Wave Sources Figure: When a stick is dipped into the water, a series of circular disturbances are created ( Roger McLassus).

3 4.4 Wave Sources A periodic oscillator can act as a wave source. If the end of a rope is connected to an oscillator (such as a moving hand), continuous pulses travel on the rope forming a wave. Oscillating electrons create electromagnetic waves in antennae. Human vocal cords, and musical instruments, create sound waves. Figure: Vibrating air colums in musical instruments create sound waves ( Infrogmation).

4 4.4 Travelling Waves Wave Pulse Wave pulse is a traveling disturbance in a medium. Travelling Wave Travelling wave is a series of travelling wave pulses. Examples of travelling waves include water waves, sound waves, and electromagnetic waves. Water and sound waves are examples of mechanical travelling waves, where disturbations travel in a medium. Electromagnetic waves do not need a medium in which to travel. The speed of electromagnetic waves in vacuum is c = ms 1.

5 4.4 Wavelength λ of a Wave cm y wavelength λ x cm Wavelength Wavelength is the shortest distance along the wave between two points in phase with one another (OR: distance travelled by the wave in one period).

6 4.4 Amplitude A of a Wave cm y amplitude A = 0.30 m x amplitude A = 0.30 m cm Amplitude Amplitude is the greatest displacement from the equilibrium position. In the figure above, the amplitude is A=0.30m from the x-axis.

7 4.4 Period T of a Wave cm y period T t s Period T of a Wave Period is the time taken for one complete oscillation (OR: time taken for one cycle to pass a given point).

8 4.4.3 Mechanical Longitudinal Wave Mechanical Longitudinal Wave A longitudinal wave is a wave in which the direction of motion of the energy transfer is parallel to the direction of motion of the particles of the medium. Sound waves are an example of mechanical longitudinal waves. Longitudinal waves can travel in all types of medium: gas, liquid and solid.

9 4.4.3 Mechanical Transverse Wave Mechanical Transverse Wave Transverse wave is a wave in which the direction of motion of the energy transfer is perpendicular to the direction of motion of the particles of the medium. Traveling pulses in a rope, or S-type Earth quake waves are examples of mechanical transverse waves. Mechanical transverse waves cannot exist in gases, because there are no intermolecular forces that could produce such motion. Electromagnetic waves are non-mechanical transverse waves, in which the electric field oscillates at right angles to the direction of the wave.

10 4.5 Wave Properties Snell s Law A wave comes from medium 1, and refracts to medium 2. Frequency of the wave stays the same, but velocity changes. θ 1 refractive index n 1, wave speed v 1 wavelength λ 1, frequency f θ 2 refractive index n 2, wave speed v 2 wavelength λ 2, frequency f According to Snell s Law, the ratio of refractive indices is n 1 = sinθ 2 = v 2 = λ 2 n 2 sinθ 1 v 1 λ 1

11 4.5 Wave Properties Snell s Law A wave comes from medium 1, and refracts to medium 2. θ 1 refractive index n 1, wave speed v 1 wavelength λ 1, frequency f θ 2 refractive index n 2, wave speed v 2 wavelength λ 2, frequency f According to Snell s Law, the ratio of refractive indices is c n 1 v = 1 c = c v 2 n 2 v 2 v 1 c = v 2 = λ 2 = sinθ 2 v 1 λ 1 sinθ 1 where c is the speed of light in vacuum.