Physics Lecture 4 PDF

90 Content of the Course ❖ Chapter 1: Physical Quantity, Units and Dimensions (1 weeks) ❖ Chapter 2: Motion in one Dimension and (2 week) ❖ Chapter 3: Vector Analysis (2 weeks) ❖ Chapter 4: Waves, Oscillations and Sound (2 weeks) ❖ Chapter 5: light lenses and mirrors (2...

90 Content of the Course ❖ Chapter 1: Physical Quantity, Units and Dimensions (1 weeks) ❖ Chapter 2: Motion in one Dimension and (2 week) ❖ Chapter 3: Vector Analysis (2 weeks) ❖ Chapter 4: Waves, Oscillations and Sound (2 weeks) ❖ Chapter 5: light lenses and mirrors (2 weeks) ❖ Chapter 6: Heat and Thermodynamics (2 weeks) ❖ Chapter 7: Electricity & Magnetism (2 weeks) Physics Prof. Dr. E. F. Abo Zeid 10/5/2024 91 Chapter 4 Waves, Oscillations, and Sound Physics Prof. Dr. E. F. Abo Zeid 10/5/2024 92 Disturb the surface of water and you create water waves. Disturb the molecules of air in the room and you create a sound wave. Disturbing the electromagnetic fields filling space causes electromagnetic waves (light!). Physics Prof. Dr. E. F. Abo Zeid 10/5/2024  Electromagnetic Waves 93  Actually, it is a bit more subtle than that.  If the electric field is varying at some location, that will cause changing magnetic fields nearby.  And the changing magnetic fields will cause new electric fields beyond that. And so on. ❑Shaking a magnet causes changing magnetic fields, which cause electric fields, which cause magnetic fields, etc. ❑Any changes to electric or magnetic fields causes electromagnetic waves to propagate away from the disturbance. ❑Electromagnetic waves are light. Physics Prof. Dr. E. F. Abo Zeid 10/5/2024 A picture of light  Light is a transverse wave of varying electric and magnetic fields.  This pattern of fields moves through space, each location experiencing oscillating fields. Physics 10/5/2024 94 Prof. Dr. E. F. Abo Zeid  Radio Lowest Learn the EM Spectrum frequency and energy 95Microwave Part of radio category Infrared Frequencies just below visible Visible Light What we can see Ultraviolet Higher energy than visible X-Rays Still higher energy and frequency Gamma Rays ❑ Again, higher frequency is higher energy. Highest frequencies ❑ All EM waves travel at the speed of light, c = 3 x 108 m/s. ❑ c = λ f, λ = wavelength, light with higher Physics frequenciesProf.has Dr. E.aF.shorter Abo Zeid wavelength. 10/5/2024  Introducing … Roy G Biv 96  We perceive the different frequencies of visible light as different colors.  The rainbow is in the order of frequencies.  Red, Orange, Yellow, Green, Blue, Indigo, and Violet (ROY G BIV) is the order from lowest frequency to highest among light. Q. Why we can’t see infrared? Our eyes contain chemicals that can be triggered into sending a nerve impulse when hit by light. Our eyes have evolved to detect a range of frequencies that we call visible light. If we could see infrared, then we would have called those wavelengths visible light! Physics Prof. Dr. E. F. Abo Zeid 10/5/2024  Q. Why are ultraviolet (UV), X-ray, and Gamma Ray dangerous? 97  These are high-energy forms of radiation.  They have enough energy to break chemical bonds in cells - like in strands of DNA.  The body can usually repair such damage but too much and the repairs don’t happen, and you get problems like cancers (cells that grow out-of-control). Physics Prof. Dr. E. F. Abo Zeid 10/5/2024  Q. How do microwave ovens work? 98  The frequencies of microwave radiation happen to be frequencies that are readily absorbed by water molecules.  Microwaves produced in the oven bounce off the walls until they are absorbed - usually by water molecules.  Wet things get hot in the oven, dry things do no get as hot. Q. Does red light really have less energy than blue light? Yes. Higher frequency light carries more energy and blue has a higher frequency than red. For various reasons, we commonly associate red with hot and blue with cold, but the blue light waves carry more energy than the red ones. Physics Prof. Dr. E. F. Abo Zeid 10/5/2024  Simple Harmonic Motion - Perfect Periodic Motion 99 Physics Prof. Dr. E. F. Abo Zeid 10/5/2024  Simple Harmonic Motion Parameters 100 Physics Prof. Dr. E. F. Abo Zeid 10/5/2024 101 Physics Prof. Dr. E. F. Abo Zeid 10/5/2024  Mechanical Waves 102 Physics Prof. Dr. E. F. Abo Zeid 10/5/2024  Sinusoidal Waves 103 Physics Prof. Dr. E. F. Abo Zeid 10/5/2024  Example 104 Figure. A sinusoidal wave of wavelength λ= 40.0 cm and amplitude A= 15.0 cm. The wave function can be written in the form y = A cos(kx-wt ). H.W. Find the maximum velocity &acceleration. Physics Prof. Dr. E. F. Abo Zeid 10/5/2024  Superposition of Waves Interference 105 Physics Prof. Dr. E. F. Abo Zeid 10/5/2024 Standing Waves and Resonance 106 Physics Prof. Dr. E. F. Abo Zeid 10/5/2024  Resonance in Air Columns 107 Physics Prof. Dr. E. F. Abo Zeid 10/5/2024  Example: 108 1. A pipe open at both ends resonates at a fundamental frequency fopen. When one end is covered and the pipe is again made to resonate, the fundamental frequency is fclosed. Which of the following expressions describes how these two resonant frequencies compare? 2. A section of drainage culvert 1.23 m in length makes a howling noise when the wind blows. (a) Determine the frequencies of the first three harmonics of the culvert if it is open at both ends. Take v=343 m/s as the speed of sound in air. Physics Prof. Dr. E. F. Abo Zeid 10/5/2024 109  Calculate the 1 st harmonic frequency for a one closed end air column if the speed of sound in air is 320 m/s and the column length is 2.5 cm. Physics Prof. Dr. E. F. Abo Zeid 10/5/2024  Sound Waves 110  Sound is a periodic motion results from the atoms displacement from the equilibrium position. This makes a change in pressure. Physics Prof. Dr. E. F. Abo Zeid 10/5/2024 Example: 111 Physics Prof. Dr. E. F. Abo Zeid 10/5/2024  Sound level in Decibels (dB) 112 Physics Prof. Dr. E. F. Abo Zeid 10/5/2024 113 Thanks for your attention Physics Prof. Dr. E. F. Abo Zeid 10/5/2024