Waves

• When waves travel through a medium, the particles oscillate and transfer energy between each other, but overall, the particles stay in the same place.
• The amplitude is the maximum displacement.
• The wavelength is the distance between the same point of 2 waves.
• S-waves are transverse and only travel through solids at a slower speed than p-waves.
• P-waves are longitudinal and can travel through solids and liquids at a faster speed than s-waves.
• Frequency is the number of complete waves passing a point per second (hertz).
• From the frequency, you can find the period of a wave, which is the amount of time it takes for a full cycle of the wave.
• In transverse waves, the oscillations are perpendicular to the direction of energy transfer, they include: all electromagnetic waves, ripples and waves in water, a wave of a string.
• In longitudinal waves, the oscillations are parallel to the direction of energy transfer, they include: sound waves in air, such as ultrasound, shock waves.
• The wave speed is the speed at which energy is being transferred (or the speed the wave is moving at).
• The wave equation applies to all waves.
• WAVE SPEED=FREQUENCY x WAVELENGTH.
• By attaching a signal generator to a speaker you can generate sounds with a specific frequency.
• You can use 2 microscopes and oscilloscope to find the wavelength.
• Set up the oscilloscope so the detected waves at each microphone are shown separately.
• Start with both microphones next to the speaker and move one away until the two waves are aligned on the display, but have moved one wavelength apart.
• Measure the distance between the microphones to find one wavelength.
• Use the equation (speed=frequency x wavelength) to find the speed, the frequency is set on the signal generator.
• The speed of sound in air is around 300 m/s, results should roughly agree with this.
• Use a signal generator attached to a ripple tank dipper to set the frequency.
• Use a lamp to see water crests on the screen below-the shadows should be the same size as the waves.
• The distance between each shadow line is one wavelength.
• Measure ten wavelengths and divide by 10 to find the average wavelength.
• You could also take a photo of the waves to find the wavelength instead.
• Use the equation to calculate the wave speed.
• This allows you to measure wavelength without disturbing the waves.
• Set up a signal generator, vibration transducer, string pulley and mass, turn on the first two and the string will start to vibrate.
• Adjust the frequency until there’s a clear wave, depending on the length of the string.
• Measure wavelength by finding the mean flag wavelength, then doubling it.
• The frequency is what the signal generator is set to.
• You can find the speed of the wave using the equation.
• Reflection happens when waves arrive at a boundary between two materials, 3 things can happen: they are absorbed, transferring energy to the materials energy stores, they are transmitted and carry on travelling through material-leading to refraction, they are reflected.
• In all reflected waves, angle of incidence = angle of reflection.
• The angle of incidence is between the incoming wave and the normal, the angle of reflection is between the reflected wave and the normal.
• The normal is perpendicular to the surface at the point of incidence, usually shown as a dotted line.
• The boundaries between different substances refract light different amounts.
• When transmitted radio waves reach a receiver, they are absorbed and the energy carried by the waves is transferred to the electrons in the material of the receiver, causing the electrons to oscillate and, if the receiver is part of a complete electrical circuit it generates an AC.
• Radio waves are produced by alternating currents, which are made of oscillating charges, and the frequency of the waves produced is the frequency of the AC.
• The signal is received by a satellite dish on the ground, there is a slight time delay because of the long distance the signal has to travel.
• The optical density of a material is a measure of how quickly light can travel through it, with higher densities slowing down light.