Foundation Year Program WAVES 2015 -16 Lab

Foundation Year Program WAVES 2015 -16

Lab rearrangements for Thursday (to compensate for Kurban Ait national holiday) (there are no classes on Thursday 24 September) Lab Practicals are rearranged for the following groups: Group 16 Wednesday 11 am (23 Sept) Da. Vinci lab 21 Tuesday 9 am (22 Sept) Da. Vinci lab (Group 21 – this is an extra lab session) 22 Monday 4 pm (21 Sept) Newton lab 23 Friday 11 am (25 Sept) Biology lab 24 Friday 11 am (25 Sept) Chem lab

Foundation Year Program Lecture Outline ØNature of waves ØSimple harmonic motion ØLongitudinal vs. Transverse waves ØStanding vs. Travelling waves ØSound waves ØHuman ear ØLight waves ØCoherence ØInterference ØDiffraction ØApplications in technology 2015 -16

There is no statics in the Universe! Everything is in motion! In periodic motion! Whenever there is a periodic motion there are waves! Every particle in the Universe is a vibrating wave! (String Theory)

Foundation Year Program Nature of waves Mechanical Electromagnetic ? Gravity waves Vibrations of vacuum! Requires a medium to propagate! Can propagate both in medium and vacuum! Propagates in spacetime continuum! 2015 -16

Foundation Year Program Motion of Waves – and Particles in the Wave 2015 -16

Foundation Year Program Simple Harmonic Motion Simple harmonic motion is a repetitive movement back and forth through an equilibrium, or central, position, so that the maximum displacement on one side of this position is equal to the maximum displacement on the other side. (A modified excerpt from Encyclopedia Britannica ) Each particle in a wave undergoes SHM! 2015 -16

Foundation Year Program Basic parameters and terminology Simplest waves: Sinusoidal waves! Frequency = y (Displacement) x (Position) Wavelength Amplitude y (Displacement) 1 Period t (Time) Period 2015 -16

Foundation Year Program Types of Waves Progressive or Standing Waves Transverse Longitudinal Mechanical Non-Mechanical 9 2015 -16

Foundation Year Program Each particle in a wave undergoes SHM! Longitudinal Vibration of particles Direction of wave propagation Transverse Vibration of particles Direction of wave propagation Particles do not travel with the wave. They simply oscillate (vibrate) around the equilibrium point. 2015 -16

More on longitudinal waves Sound wave Wave on a slinky

Foundation Year Program Travelling wave For a travelling wave the energy is travelling with the wave! 2015 -16

Foundation Year Program Standing waves - Examples For a standing wave the energy is stored within a wave! Standing wave occurs when a wave reflected from a boundary overlaps with the incident wave! 2015 -16

Foundation Year Program Finding the speed of light with using a chocolate bar in a microwave! ½ wavelength 2015 -16

Foundation Year Program Electromagnetic waves around us! 2015 -16

Foundation Year Program Electromagnetic Waves Electromagnetic radiation (waves) is the flow of energy at the universal speed of light through free space or through a material medium in the form of the electric and magnetic fields that make up electromagnetic waves such as radio waves, visible light, and gamma rays. In such a wave, time-varying electric and magnetic fields are mutually linked with each other at right angles and perpendicular to the direction of motion. (A modified excerpt from Encyclopedia Britannica ) 2015 -16

Foundation Year Program Electromagnetic Waves 2015 -16

Foundation Year Program Sound Ear drum Sound is a mechanical wave of pressure and displacement of particles of the medium such as air or water. In physiology sound is the reception of such waves and their perception by the brain. The ratio between the quietest and loudest sound intensities we can hear is 10, 000, 000 (10 trillion or 1013). Because the range is very large we use the logarithmic scale to express sound intensity level. 2015 -16

Foundation Year Program Behavior of Waves act in special ways when they reach a barrier, and when they reach one or two small holes in a barrier. When they reach a barrier, they reflect, When they reach the edge of a barrier, they diffract, When they reach one hole*, they become spatially coherent, When two coherent waves reach two holes, they interfere with each other. * NOTE: for this to be true, the wavelength must be approximately 1 -5 times the size of the hole 2015 -16

Foundation Year Program Reflection of a wave is the process where a wave hits a barrier, bounces off, and returns into the same medium where it came from. 2015 -16

$Foundation Year Program Diffraction is the spreading of waves around obstacles or barriers. Huygens's$

Foundation Year Program Diffraction is the spreading of waves around obstacles or barriers. Huygens's principle 2015 -16

$Foundation Year Program Laser diffraction using reflection diffraction grating Diffraction pattern observed on the$

Foundation Year Program Laser diffraction using reflection diffraction grating Diffraction pattern observed on the screen. 2015 -16

Foundation Year Program Coherence, a fixed relationship between the phase of waves in a beam of radiation of a single frequency. Two beams of light are coherent when the phase difference between their waves is constant; they are noncoherent if there is a random or changing phase relationship. (A modified excerpt from Encyclopedia Britannica ) Light is coherent when each wave has the same Wavelength & Frequency and there is a constant distance between crests. 2015 -16

Foundation Year Program Interference - Examples 2015 -16

Foundation Year Program How did these grid waves formed? 2015 -16

Foundation Year Program Noise cancelling headphones 2015 -16

Foundation Year Program To summarize… We are surrounded by waves. . . Waves differ in nature (mechanical. E&M, gravity). Waves differ in the way they vibrate and propagate. Waves can be either travelling or standing. Waves can reflect from barriers. If specific conditions are satisfied they can also bend over a barrier (diffract). • Under certain conditions (coherence) waves can interfere with each other. Interference can be of two types – constructive and destructive. • • • 2015 -16