topic 3 waves

• microphone changes sound waves to an electrical signal, the oscilloscope then shows what electric waves look like
• the faster the vibrations, higher the pitch (frequency) of the sound
• human hearing is 20-20,000hz, above 20,000 is considered an ultrasound
• investigating the speed of sound in air, stop watch, block of wood, at least 100m distance, start stopwatch when they see wood bang together, stop when they hear sound, use equation speed= distance divided by time, repeat 3x for accuracy
• greater the amplitude louder the sound
• wave speed equation, wave speed= frequency x wave length
• refractive index equation, refractive index = sin I divided by sin r, then do sin -1
• frequency equation, frequency = 1/ time period
• critical angle equation, sin critical angle = 1/ refractive index, then do sin -1
• electromagnetic spectrum, radio waves (long wavelength, short frequency), micro waves, infrared, visible light, ultra violet, x-rays, gamma rays (short wavelength, high frequency)
• sound waves are longitudinal waves which can be reflected or refracted
• gamma rays exposure can cause cancer, mutations so should wear lead clothing
• radio waves are used for broadcasting and communications
• visible light is used for optical fibres and photography
• period is the time taken for one cycle to complete
• micro waves are used for cooking and satellite transmissions
• infrared exposure can cause skin burns
• frequency is the number of cycles in a second
• ultraviolet is used for fluorescent lamps
• gamma rays are used for sterilising food and medical stuff
• x-rays are used for observing the internal structure of objects and materials, medical
• infrared is used for heaters and night vision equipment
• light waves are transverse waves which can be reflected
• longitudinal waves are when oscillation is parallel to the wave direction, transverse is when oscillation is perpendicular to the wave direction
• waves transfer energy and information without transferring matter
• wavefront is the moving line which joints all points on a crest of a wave
• microwaves exposure causes internal heating of body tissue
• all waves can be reflected or refracted
• ultraviolet exposure can cause damage to surface cells and blindness
• critical angle is the smallest incident angle to result in a total internal reflection
• law of reflection, angle of incidence = angle of reflection
• Illustration of reflection

  
• Wavelength

  
• amplitude

  
• doppler effect is when a wave is emitted from a moving object, the apparent wavelength and frequency changes