Waves PDF

PROPERTIES AND BEHAVIOR OF WAVES Medical Physics Learning Objectives Describe what is a wave. Infer that waves carry energy. Differentiate transverse from longitudinal waves and mechanical from electromagnetic waves. Relate the characteristics of waves. Waves...

PROPERTIES AND BEHAVIOR OF WAVES Medical Physics Learning Objectives Describe what is a wave. Infer that waves carry energy. Differentiate transverse from longitudinal waves and mechanical from electromagnetic waves. Relate the characteristics of waves. Waves What is a wave? Waves can occur whenever a system is disturbed from equilibrium and when the disturbance can travel, or propagate, from one region of the system to another. *Medium- material that is instrumental for the disturbance to move. Parts of a Wave  Parts of a Wave The resting position is the spot where the wave begins disturbing the medium.  Parts of a Wave The amplitude is the maximum displacement from the rest position. It is the height of the crest or depth of a trough measured from the normal undisturbed position. Parts of a Wave The wavelength, λ, is the distance between two successive crests or two successive troughs. Parts of a Wave The crest is the highest point of peak of the wave. The trough is the lowest point of a wave. Types of Waves *According to the presense and absence of a medium. Mechanical Waves Electromagnetic Waves Mechancial Waves A mechanical wave is a disturbance that travels through some material or substance called the medium for the wave.  Transverse Waves A transverse wave is a wave in which particles of the medium move in a direction perpendicular to the direction that the wave moves. *be very careful to distinguish between the motion of the transverse wave along the string and the motion of a particle of the string. The wave moves with constant speed v along the length of the string, while the motion of the particle is simple harmonic and transverse (perpendicular) to the length of the string Longitudinal Waves A longitudinal wave is a wave in which particles of the medium move in a direction parallel to the direction that the wave moves. Surface Waves A wave in which particles of the medium undergo a circcular motion. The displacements of the water have both longitudinal and transverse components.  The disturbance travels or Waves transport propagates with a definite speed through the medium. energy, but not The medium itself does not travel through space; its individual matter, from one particles undergo back-and-forth or up-and-down motions around their region to another. equilibrium positions. To set any of these systems into motion, we have to put in energy by doing mechanical work on the system. What type of wave is the wave” shown on this slide?  Characteristics of a Wave The frequency, f, is the number of crests or troughs that pass a point per second. This is equivalent to the number of complete waves generated per second. Frequency is measured in terms of hertz (Hz). Characteristics of a Wave  Characteristics of a Wave The period, T, is the time taken to generate one complete wave. It is also the time taken for the crests, or any given point on the wave, to move a distance of one wavelength. Characteristics of a Wave Characteristics of a Wave Suppose the wave makes 2 vibrations per second, how much time is required to complete one vibration? Characteristics of a Wave Unknown: period Given: 2 vibrations per second = 2 Hz Formula: T= 1/f Solution: T= 1/f T= 1/2Hz T= 1/2 s Characteristics of a Wave The speed, v, of the wave is the distance moved by a wave in one second. *The rate at which the wave travels at a particular point. Speed of a Wave Since the wave crest travels a v= speed of the wave distance of one wavelength in λ= wavelength one period, the wave speed, T= period v = λ/T or ν = fλ f= frequency Speed of a Wave Since the wave crest travels a v= speed of the wave distance of one wavelength in λ= wavelength one period, the wave speed, T= period v = λ/T or ν = fλ f= frequency 𝑓 λ 𝑣= 1 1 𝑓 Review What happens to the frequency of a wave if its wavelength decreases? A) The frequency increases B) The frequency decreases C) The frequency remains the same Review What happens to the frequency of a wave if its wavelength decreases? A) The frequency increases B) The frequency decreases C) The frequency remains the same Review What is the unit used to measure frequency? A) Watts (W) B) Meters/Second (m/s) C) Hertz (Hz) Review What is the unit used to measure frequency? A) Watts (W) B) Meters/Second (m/s) C) Hertz (Hz) Name and label the type of wave illustrated below. WAVE Name and label the type of wave illustrated below. LONGITUDINAL WAVE RAREFACTION COMPRESSION Name and label the type of wave illustrated below. WAVE Name and label the type of wave illustrated below. TRANSVERSE WAVE CREST TROUGH Sample Problems Two waves travel on the same string. Is it possible for them to have (a) different frequencies; (b) different wavelengths; (c) different speeds; (d) different amplitudes; (e) the same frequency but different wavelengths? Explain your reasoning. Answer (a) different frequencies Yes, it is possible for them to have different frequencies because frequency corresponds to the simple harmonic motion of the particles which comes from the oscillator that began the disturbance in the first place. Answer (b) different wavelengths Yes, it is possible for them to have different wavelengths because, according to relation v=f⋅λ, if the frequencies are different and the speed is the same, then the wavelength must be different. Answer (c) different speeds No, it is not possible for them to have different speeds because wave speed depends on the medium (the string). Since the string has same tension and same linear mass density along its length, the speed must be the same. F= tension μ=linear mass density (mass per unit length) Answer (d) different amplitudes Yes, it is possible for them to have different amplitude because the amplitude corresponds to the amount of energy given to the wave which comes from the external force that started the disturbance. Answer (e) the same frequency but different wavelengths No, it is not possible because to the relation v=f⋅λ, if they have the same frequency and the same speed (from part c), they must have the same wavelengths.  Sample Problems For the wave motions discussed, does the speed of propagation depend on the amplitude? What makes you say this? Answer No, the speed of propagation does not depend on the amplitude. It only depends on the medium properties.  Sample Problems The speed of sound in air at 20 ℃ is 344 m⁄s (a) What is the wavelength of a sound wave with a frequency of 784 Hz, corresponding to the note G_5 on a piano, and how many seconds does each vibration take? Answer Step 1-- Knowns speed of a periodic wave v with wavelength λ and frequency f is given by: v=f⋅λ (equation 1) the relation between the frequency and the time period is given by: T= 1/f (equation 2) Answer Step 2-- Given the frequency of the sound wave (corresponding to G_5 on a piano) is f=784 Hz, and the speed of sound in air at 20 ℃ is v=344 m/s. Answer Step 3-- Calculations Sound is a periodic wave, so we can use equation (v=f⋅λ); We plug our values for v and f into the equation, so we get: Answer Step 4 We know that the time each vibration takes is the definition of a time period T, so we substitute for f into equation (2), so we get:  1234567899. 9 0.0000000123 1.23x10 −8 1.23x10 Types of Waves *According to the presense and absence of a medium. Mechanical Waves Electromagnetic Waves Concept Check Which type of wave requires a medium to travel through? A) microwave B) radio wave C) mechanical wave Question 5 Which type of wave requires a medium to travel through? A) microwave B) radio wave C) mechanical wave ELECTROMAGNETIC WAVES Electromagnetic waves are a self-propagating transverse wave of oscillating electric and magnetic fields. ELECTROMAGNETIC WAVES developed a scientific theory to explain electromagnetic waves noticed that electrical fields and magnetic fields can couple together to form electromagnetic waves. summarized this relationship between electricity and magnetism into what are now referred to as "Maxwell's Equation" ELECTROMAGNETIC SPECTRUM Electromagnetic waves can be classified and arranged according to their various wavelengths/frequencies; this classification is known as the electromagnetic spectrum.  TYPES OF ELECTROMAGNETIC RADIATION Radio waves Microwaves Infrared Visible Light  TYPES OF ELECTROMAGNETIC RADIATION Visible Light Ultraviolet X-Radiation Gamma Ray 01 RADIOWAVES has a frequency 3 Hz to 300 Hz James Clerk Maxwell who made the first prediction about radio waves but it was Heinrich Hertz who showed that radio waves can be produced and transmitted. has a lowest frequency and longest wavelength that makes it suitable for telecommunication. 01 RADIOWAVES These are the waves that allow us to listen to the radio. They have long wavelengths and low frequencies. Radio waves are used for broadcasting music, news, and other information. 02 MICROWAVES Ranges from 300 MHz (3 x 10^8 Hz) to 300 GHz (3x 10^11 Hz). it has a frequency higher than the frequency of radio waves. The prefix “micro” in microwaves signifies that it has a micrometer wavelengths compared to traditional radio waves. 02 MICROWAVES Microwaves have shorter wavelengths and higher frequencies than radio waves. They are used in microwave ovens to cook and heat food. They are also used for communication, such as cell phones and Wi-Fi. 03 INFRARED RADIATION has a frequency extending from 300 GHz (3x10^11 Hz) to THz (4.05x10^14 Hz). It has a frequency higher than microwave and lower than the visible light. Infrared radiation is also called heat radiation so it can be detected using a thermometer. 03 INFRARED RADIATION Infrared radiation is sometimes called "heat radiation" because we feel it as warmth. It has longer wavelengths than visible light. Infrared radiation is used in devices like TV remote controls and thermal cameras. 04 VISIBLE LIGHT it is the only EM waves that is visible to unaided eyes. It lies between infrared and ultraviolet rays. 04 VISIBLE LIGHT This is the type of electromagnetic radiation that allows us to see the world around us. Visible light comes in different colors, like red, orange, yellow, green, blue, indigo, and violet. Each color has a different wavelength. 05 ULTRAVIOLET RADIATION has a frequency extends from 790 THz (7.90x10^14 Hz) and 30 PHz (3x10^16 Hz). Ultraviolet means “beyond violet”, ultra came from the Latin word beyond and violet is the visible light that contains highest frequency. 05 ULTRAVIOLET RADIATION UV radiation has shorter wavelengths and higher frequencies than visible light. It comes from the sun and is responsible for causing sunburns. We can't see UV radiation, but it can be harmful to our skin and eyes. 06 X- RADIATION has a frequency lies between 30 PHz (3x 10^16 Hz) and 30 EHz (3x10^19 Hz). It has the ability to penetrate opaque materials, it can pass through soft tissues but can filtered by dense materials like the bone. 06 X- RADIATION The first ever X-ray taken of a human (above, on December 22, 1895) was the left hand, complete with wedding and engagement rings, of Anna Bertha Roentgen - the wife of the man who accidentally discovered a form of radiation that would change the face of medicine 06 X- RADIATION X-rays have even shorter wavelengths and higher frequencies than UV radiation. They can pass through our bodies and are used in medical imaging, like X-ray machines, to see our bones and organs.  07 GAMMA RADIATION has a frequency higher that 30 eHz (< 3 x10^19 Hz). It is the most energetic electromagnetic wave in the spectrum for it has the highest frequency and shortest wavelength. Due to its high energy gamma rays may harm human beings and the environment.  EFFECTS OF TOO MUCH EXPOSURE ON ELECTROMAGNETIC RADIATION TO living things and environment: HUMANS cancers mental disorders neurologic illnesses fetal abnormalities, cardiovascular diseases, etc.  LONG TERMS EXPOSURE OF LOW- frequency EMR from home appliances HUMANS hyperactivity, sleep disorder emotional instability.  EFFECTS OF TOO MUCH EXPOSURE ON ELECTROMAGNETIC RADIATION TO living things and environment: ANIMALS Honeybee’s loss or known as colony collapse disorder (CCD) migratory birds confusion cow’s general health problems reproductive and developmental problems of domestic animals  EFFECTS OF TOO MUCH EXPOSURE ON ELECTROMAGNETIC RADIATION TO living things and environment: PLANTS nutrient capability destroying anti-cancer ability of different vegetables. THANK YOU FOR LISTENING!