Waves. Electromagnetic & Mechanical Waves

Transcription

1 Waves Electromagnetic & Mechanical Waves

2 Wave Definition: A disturbance that transfers energy from place to place. Molecules pass energy to neighboring molecules who pass energy to neighboring molecules who pass energy to their! All waves are produced by vibrations Waves will travel as long as there is energy to carry

3 Waves (cont d) What carries waves? A medium, a medium is the material through which a wave travels. A medium can be a gas, liquid, or solid. Not all waves need a medium to travel (ie: light and radio waves can travel through space)

4 What causes waves? Waves are created when a source of energy causes a medium to vibrate. A vibration is a repeated back and forth or up and down motion. Mechanical waves are waves that can only travel through a medium.

5 Mechanical Waves are classified based on how they move Transverse: Waves that move the medium at right angles to the direction in which the waves are traveling Transverse means across. Compressional: Matter vibrates in the same direction as the wave travels.

6 Oh, and surface waves - These are combinations of transverse and longitudinal waves

7 parts of all waves Amplitude Wavelength Frequency Speed Rest

8 Transverse waves have 2 main parts Crest Trough

9 Compressional waves have 2 main parts Compressions Rarefactions

10 Rest position = place where there is no disturbance. 10

11 Amplitude Maximum distance the particles of the medium carrying the wave move away from their rest positions. The farther the medium moves the larger the amplitude of the resulting waves. You can find the amplitude of a transverse wave by measuring the distance from crest to crest or crest to trough. The greater the amplitude the greater the amount of energy. The amplitude of a longitudinal wave is a measure of how compressed or rarefied the medium becomes. Measured in meters

12 Wavelength (m) Frequency (Hz) Speed (m/s) The distance between two corresponding parts of a wave is its wavelength. The number of complete waves that pass a given point in a certain amount of time. The speed, wavelength, and frequency of a wave are related to each other by a mathematical formula. Transverse measure from crest to crest or trough to trough. The number of vibrations per second. Longitudinal measure from one compression to the next. Frequency measured in hertz (Hz). Wavelength = speed/frequency Frequency = speed/wavelength Speed = wavelength x frequency Long λ = low energy Short λ = high energy High frequency = high energy = short λ Low frequency = low energy = long λ

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14 THe Law of Reflection Angle of incidence (i) = angle of reflection (r)

15 Types of Reflection A single, incoming ray is reflected in one single, outgoing ray. Reflected rays scatter in all directions.

16 Refraction - Bending of a wave caused by a change in its speed as it moves from one medium to another - The greater the change in speed, the more the wave bends - Causes rainbows! (White light is refracted by water droplets)

17 Diffraction - An object causes a waves to change direction and bend towards it - **Both refraction and diffraction cause waves to bend. However, refraction occurs when waves pass through an object while diffraction occurs when waves pass around an object.**

18 Shadows - Shadows are the place where light is blocked - Edges are blurry because of diffraction

19 Interference - When two or more waves overlap and combine to form a new wave - Can be constructive or destructive

20 Electromagnetic Waves - LIght It is an electromagnetic wave (EM wave). Does not require a medium to travel Consists of changing electric and magnetic fields (fields are forces that push and pull on another object without touching it) Light travels in straight lines Light travels VERY FAST around 300,000,000 meters per second. Study Jamz

21 Electromagnetic Spectrum

22 Electromagnetic Spectrum (cont d) Radio Waves Some of the longest wavelengths and lowest frequencies Used for broadcasting radio signals TV signals are also carried by radio waves Radio waves cannot be heard, but they carry energy that can be converted into sound. Amplitude modulation (Am) radio - broadcasts info by varying the amplitude of the carrier wave Frequency modulation (FM) radio - Broadcasts by varying the frequency of the carrier wave Each radio station is assigned a particular radio frequency for their broadcast - this specific frequency = carrier wave

23 Electromagnetic Spectrum (cont d) Microwaves Shorter wavelength and higher frequencies Cell phones send and receive signals using microwaves Radar guns used to check speed of a car also use microwaves Video Infrared Waves Shorter wavelengths and higher frequencies than microwaves do Almost all things give off infrared waves The amount of waves given off by an object depends on the object temperature warmer objects give off more infrared waves We can not see infrared waves without assistance from a machine.

24 Electromagnetic Spectrum (cont d) Visible Waves Very narrow range of wavelengths and frequencies that humans can see Shorter wavelengths and higher frequencies than infrared waves. Visible light from the sun is white light and is a combination of all wavelengths We see different wavelengths of light as different colors.

25 Visible Waves!

26 Electromagnetic Spectrum (cont d) Ultra Violet Light Electromagnetic wave produced by the sun Shorter wavelengths and higher frequencies than visible light Too much ultraviolet light can cause a sunburn and skin cancer, wrinkles, and damage to the eyes Ultraviolet lamps are used to kill bacteria on food and surgical tools Needed by skin cells to produce vitamin D. X-Rays They can pass through many materials Too much exposure to x-rays can also damage or kill living cells Also used for security devices

27 Electromagnetic Spectrum (cont d) Gamma Waves Shortest wavelength Can penetrate most materials very easily Used to treat some forms of cancer Also used to kill harmful bacteria in foods

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