Waves

• Waves may be either transverse or longitudinal. The ripples on a water surface are an example of a transverse wave. Longitudinal waves show areas of compression and rarefaction. Sound waves travelling through air are longitudinal
• describe the difference between longitudinal and transverse waves.

  Transverse waves cause the medium to move perpendicular to the direction of the wave. Longitudinal waves cause the medium to move parallel to the direction of the wave
• describe the difference between longitudinal and transverse waves.

  Transverse waves cause the medium to move perpendicular to the direction of the wave. Longitudinal waves cause the medium to move parallel to the direction of the wave
• The amplitude of a wave is the maximum displacement of a point on a wave away from its undisturbed position. The wavelength of a wave is the distance from a point on one wave to the equivalent point on the adjacent wave. The frequency of a wave is the number of waves passing a point each second
• T=1/f

  period, T, in seconds, s frequency, f, in hertz, Hz The wave speed is the speed at which the energy is transferred (or the wave moves) through the medium.
• All waves obey the wave equation - wave speed = frequency × wavelength v  = f  λ wave speed, v, in metres per second, m/s frequency, f, in hertz, Hz wavelength, λ, in metres, m
• describe a method to measure the speed of sound waves in air

  timing how long it takes for the sound waves to travel a known distance through a medium.,
• describe a method to measure the speed of ripples on a water surface.

  Count the number of waves passing a point in ten seconds then divide by ten to record frequency. Calculate the speed of the waves using: wave speed = frequency × wavelength.
• Set up the ripple tank with about 5cm depth of water.Adjust the height of the wooden rod so it touches the surface of the water.Switch on the lamp and motor and adjust until low frequency waves can be clearly observed.Measure length of a no. of waves then divide by the no. of waves to record wavelength. Count the no. of waves passing a point in ten seconds then divide by ten to record frequency.Calculate the speed of the waves using: wave speed = frequency × wavelength.
• Electromagnetic waves are transverse waves that transfer energy from the source of the waves to an absorber. Electromagnetic waves form a continuous spectrum and all types of electromagnetic wave travel at the same velocity through a vacuum (space) or air. The waves that form the electromagnetic spectrum are grouped in terms of their wavelength and their frequency. Going from long to short wavelength (or from low to high frequency) the groups are: radio, microwave, infrared, visible light (red to violet), ultraviolet, X￾rays and gamma rays.
• Our eyes only detect visible light and so detect a limited range of electromagnetic waves.
• Our eyes only detect visible light and so detect a limited range of electromagnetic waves.
• examples that illustrate the transfer of energy by electromagnetic waves.

  radio waves – television and radio (including Bluetooth) microwaves – satellite communications, cooking food. infrared – electrical heaters, cooking food, infrared cameras. visible light – fibre optic communications.
• Different substances may absorb, transmit, refract or reflect electromagnetic waves in ways that vary with wavelength. Some effects, for example refraction, are due to the difference in velocity of the waves in different substances
• investigate how the amount of infrared radiation absorbed or radiated by a surface depends on the nature of that surface

  Place a Leslie cube on a heat-resistant mat. Fill it, almost to the top, with boiling water and replace the lid.Leave for one minute. This is to enable the surfaces to heat up to the temperature of the water. Use the infrared detector to measure the intensity of infrared radiation emitted from each surface, or the temperature of the surface. Make sure that the detector is the same distance from each surface for each reading.
• Radio waves can be produced by oscillations in electrical circuits. When radio waves are absorbed they may create an alternating current with the same frequency as the radio wave itself, so radio waves can themselves induce oscillations in an electrical circuit. Changes in atoms and the nuclei of atoms can result in electromagnetic waves being generated or absorbed over a wide frequency range. Gamma rays originate from changes in the nucleus of an atom.
• Ultraviolet waves, X-rays and gamma rays can have hazardous effects on human body tissue. The effects depend on the type of radiation and the size of the dose. Radiation dose (in sieverts) is a measure of the risk of harm resulting from an exposure of the body to the radiation.
• 1000 millisieverts (mSv) = 1 sievert (Sv)
• Ultraviolet waves can cause skin to age prematurely and increase the risk of skin cancer. X-rays and gamma rays are ionising radiation that can cause the mutation of genes and cancer.
• Ultraviolet waves can cause skin to age prematurely and increase the risk of skin cancer. X-rays and gamma rays are ionising radiation that can cause the mutation of genes and cancer.
• Electromagnetic waves have many practical applications. For example: • radio waves – television and radio • microwaves – satellite communications, cooking food • infrared – electrical heaters, cooking food, infrared cameras • visible light – fibre optic communications • ultraviolet – energy efficient lamps, sun tanning • X-rays and gamma rays – medical imaging and treatments
• In a vacuum all electromagnetic waves travel at the same velocity
• Explain why it is important that the earth's atmosphere absorbs gamma rays emitted by the sun


  so people are not exposed to as much gamma radiation because gamma radiation can damage human tissue
• Some microwaves aren't absorbed by the earth's atmosphere. Why is this useful 


  microwaves are used in satellite communications
• Which is exposure to uv radiation harmful

  can cause skin cancer / premature ageing
• Measuting Frequency of awareness wave • use a stopclock • count the number of waves passing a point in a fixed time period • divide the time by the number of waves to determine the time for one wave, T • f = 1/T • read the frequency off the oscillator
• Mwasuring Wavelength of a water wave • use a camera to freeze the image • use a metre rule to measure the distance between two wavefronts • count the number of waves between the wavefronts • divide distance by the number of waves to determine λ
• Measuring Velocity of a water wave • determine a mean value of frequency • determine a mean value of wavelength • measure the time it takes one wavefront to travel the length of the screen • measure the length of the screen • speed = distance / time
• How does movement of aplastic duck show waves are transverse

  moves perpendicular to the direction of wave travel