Waves

• Waves transfer energy from one place to another
• Wave Speed (m/s) = Frequency (Hz) x Wavelength (m)
• The amplitude is the largest distance that a point on a wave moves from its rest position or the distance between the rest position and the peak or the trough.
• The wavelength is the distance between two adjacent wavefronts. For transverse waves, this is the distance between two adjacent peaks.
• Frequency (Hz) = number of oscillations/time (s)
• A transverse wave causes the particles in the medium (the substance that the wave travels through) to vibrate at right angles (perpendicular) to the direction of the wave’s motion. 
• A longitudinal wave causes the medium’s particles to vibrate in the same direction (parallel) as the wave’s motion.
• Ripple Tank Experiment(speed = distance / time)

  Equipment: Tray of water, ruler, stopwatch

  Method:

  1.Use the ruler to create a wave

  2. Use the stopwatch to identify the time it took for the wave to travel and use the ruler to identify the distance the wave travelled

  3. Use the equation speed = distance / time to find the wave speed.
• Ripple Tank Experiment (wave speed = frequency x wavelength)


  Equipment: Tray of water, ripple tank, stopwatch, camera/phone, ruler

  Method:

  1. Use the ripple tank to produce waves
  2. To find the wavelength, take a photo of the waves with the ruler beside them. Use the ruler to measure 10 wavelengths then divide the number by 10
  3. To find the frequency, take a 10-second video, count the number of waves that pass and divide the number by 10
  4. Use the equation wave speed = frequency x wavelength using the mean wavelength and mean frequency
• When waves travel from one medium to another, their speed and wavelength change but their frequency stays the same as the source is providing the same amount of oscillations.
• Speed and wavelength are directly proportional.
• Waves can be reflected, refracted, absorbed and transmitted (passed through) at the boundary between one medium (material) and another.
• Reflection- when a wave hits a flat surface and bounces off
• Refraction - when a wave changes direction due to a difference in speeds in different materials
• Transmission - when a wave passes straight through a different material. A wave that is transmitted is also likely to be refracted.
• Absorption- when most or all of a wave's energy is absorbed by a new medium
• • The angle of incidence is the angle between the incident (incoming) light ray and the normal.
  • The normal is an invisible line at 90 degrees to the plane.
• .The angle of reflection is the angle between the normal and the reflected ray

  .The normal is an invisible line at 90 degrees to the plane
• The angle of incidence = the angle of reflection
• If light slows down as it enters a new medium, this medium is “more optically dense”. When light enters a more optically dense medium, it is refracted closer to the normal. This means that the angle of refraction is smaller than the angle of incidence. If light speeds up as it enters a new medium, this medium is "less optically dense". When light enters a less optically dense medium, it is refracted further from the normal. This means the angle of refraction is larger than the angle of incidence.
• • Light speeds up when entering a less optically dense medium. When this happens, some light is refracted and some light is reflected. This is internal reflection.
  • If the angle of incidence is the same as the critical angle (the angle of incidence when the angle of refraction is 90 degrees), the light will travel along the boundary of the 2 mediums.
  • If the angle of incidence exceeds the critical angle, then all the light will be reflected. This is called total internal reflection.
• Diffraction- the spreading out of waves as they pass through a narrow gap in the surface.
• • Sound waves are longitudinal waves and can travel through solids by creating vibrations of the solid particles. The vibrations mean that sound waves travel in a series of compressions (where the medium is squashed together) and rarefactions (where the medium is stretched apart).
• • The vibrations mean that sound waves travel in a series of compressions (where the medium is squashed together) and rarefactions (where the medium is stretched apart).
• The typical human hearing range is between 20Hz and 20,000Hz. This range can change as we get older and become less sensitive to higher frequencies.
• • Ultrasound has a frequency above 20,000Hz. Humans cannot hear sounds with frequencies this high, but other animals can.
  • Dog whistles have frequencies above 20,000Hz, which is why humans cannot hear them.
  • Ultrasound is also used by doctors to perform scans of a developing foetus.
• Sound travels through solids fastest, liquids slower, and gases slowest.
• Measuring the Speed of Sound Experiment

  1. Two people stand a measured distance away from a tall, vertical wall (This distance should ideally be 100m)

  2. Person 1 makes a loud noise like knocking blocks together to make a sharp sound and repeats this every time they hear an echo

  3. Person 2 uses the stopwatch to find the time taken for a certain number of knocks (maybe 50 or 100)

  4. In the time between two successive claps, the sound travels to the wall and back

  5. Calculate the speed of sound using: speed of sound = distance to wall x 2 x number of claps / time taken
• An echo is an example of the reflection of sound.
• Uses of ultrasound waves #1

  1. Industry- When ultrasound waves enter a material, they will typically be reflected by the far side of the material. If the waves are reflected sooner than usual, we can identify a crack/fault in the material
  2. Water depth- We can use echo sounding to detect objects in deep water and to measure water depth. We send an ultrasound pulse into the water. When this pulse hits any surface, it is reflected. We can work out the distance travelled by the sound wave by recording the time between us sending the pulse and detecting the reflection.
• Uses of ultrasound waves #2

  1. Medicine- Doctors use ultrasound to scan and develop an image of a foetus. Ultrasound waves can pass through the body but some will be reflected at the boundary between two mediums. Computers can detect the reflected waves, the time it took for them to be reflected and the waves' distribution to produce a video image of the foetus
  2. Dog Training- Ultrasound has a frequency above 20,000Hz. Humans cannot hear sounds with frequencies this high, but other animals can. Dog whistles have frequencies above 20,000Hz.
• Earthquakes produce two types of seismic waves:

  . P-waves (primary) are longitudinal, seismic waves and travel at different speeds through solids and liquids.

  . S-waves (secondary) are transverse, seismic waves that can only through solids and not liquids
• . Seismic waves cannot travel through all parts of the Earth because it is made up of different materials. Scientists have been able to figure out the different materials the Earth is made out of by detecting seismic waves like the fact that Earth has a solid core followed by a liquid outer core and a mantle of changing density that causes the waves to refract
• All electromagnetic waves are transverse waves that travel at the same speed (or velocity) in a vacuum.
• Electromagnetic waves transfer energy from the source of the wave to an absorber of the wave. Gamma rays carry the most amount of energy than any other wave in the electromagnetic spectrum. Wave energy increases with frequency and decreases with wavelength.
• The seven types of electromagnetic waves in order of lowest to highest frequency are radio waves, microwaves, infrared, visible light, ultraviolet, x-rays, and gamma rays.
• • As you move from gamma rays to radio waves, the wavelengths increase and the frequencies decrease.
• Oscillations (repeating variations) in electrical circuits can produce radio waves. When radio waves are absorbed, they can create an alternating current with the same frequency as the radio wave itself. This means that radio waves can lead to oscillations in electrical circuits.
• Changes in atoms and the nuclei of atoms can result in electromagnetic waves being generated or absorbed over a wide frequency range. For example, gamma rays are caused by a change in nuclei.
• There are seven colours in the visible light spectrum: red, orange, yellow, green, blue, indigo and violet