Y10 Waves 2022 PRESENTATION, Diapositivas de Física

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WAVES

Y10 PHYSICS

STARTER

There are 5 main

oceans in the world.

can you name and

locate them?

WHAT DO THEY ALL HAVE IN COMMON?

Aims of the lesson Describe how waves move. Explain the basic properties of waves. Compare transverse and longitudinal waves Calculate wave speed, frequency and wavelength Describe how they are related. Explain reflection, refraction and diffraction of water waves Understand and use the law of reflection Draw refraction diagrams Describe experiments to investigate the refractive index Know and use Snell’s law Know the effect the medium has on the light waves traveling through it Know and use the relationship between critical angle and index of refraction

The big picture Most of our interaction with the world happens through waves. Our sight and our hearing detect vibrations or oscillations (which are both types of waves) and we build up a picture of the world around us. But what are waves? Music is made of waves. When an acoustic guitar string is played it vibrates back and forth quickly as a wave bounces from end to end. Different vibrations, and therefore different notes, are produced by strings of different thicknesses, or by altering the length of the strings with your fingers or altering the tension in the strings. The wave in the string produces sound waves in the air that pass into the body of the guitar, where they bounce back and forth inside the hollow chamber before travelling outwards through the air. The sound waves cause your eardrum to vibrate in waves, eventually sending electrical messages to your brain.

The big picture 2 Other musical instruments depend on vibrations and waves too. In wind instruments, such as a flute, blowing into the instrument that creates changes in air pressure. This sets up waves inside the flute's tube that change as you open and close different holes. When a drum is struck, vibrations are set up in the drum skin. These waves reflect back and forth from the edges, vibrating the air above and below.

https://youtu.be/9uOKEuD3xLw

Definition of waves Something that transfers energy without transferring matters! Waves transfer energy and information Waves are described as oscillations or vibrations about a fixed point

• (^) For example, ripples cause particles of water to oscillate up and down
• (^) Sound waves cause particles of air to vibrate back and forth In all cases, waves transfer energy without transferring matter
• (^) For water waves, this means it is the wave and not the water (the matter) itself that travels
• (^) For sound waves, this means it is the wave and not the air molecules (the matter) itself that travels Objects floating on water provide evidence that waves only transfer energy and not matter

WAVES SPREADING AS CIRCULAR WAVEFRONT S The arrows indicate the direction the wavefronts travel. This is known as the direction of propagation of the wave. A series of drops of water are falling into a pool at regular intervals. This acts as a point source for waves. The wavefronts show the position of the crests of the waves at a moment in time. The waves spread out in a circular pattern from the source. The ruler is the source of the waves as it is moved up and down in a tray of water. This produces a set of parallel waves moving away from The wavefronts are parallel to the source and evenly spaced if the ruler is moved at a constant rate. The waves travel perpendicular to the wavefronts.

Amplitude

• (^) Amplitude is defined as:
• (^) The distance from the undisturbed position to the peak or trough of a wave
• (^) It is given the symbol A and is measured in metres (m)
• (^) Amplitude is the maximum or minimum displacement fro m the undisturbed position

Wave length

• (^) Wavelength is defined as:
• (^) The distance from one point on the wave to the same point on the next wave
• (^) In a transverse wave:
  • (^) The wavelength can be measured from one peak to the next peak
• (^) In a longitudinal wave
  • (^) The wavelength can be measured from the centre of one compression to the centre of the next
• (^) The wavelength is given the symbol λ (lambda) and is measured in metres ( m)
• (^) The distance along a wave is typically put on the x-axis of a wave diagram

Frequency

• (^) Frequency is defined as:
• (^) The number of waves passing a point in a second
• (^) Frequency is given the symbol f and is measured in Hertz (Hz)

Wave Speed

• (^) Wave speed is the speed at

which energy is transferred through a

medium

• (^) Wave speed is defined as:
• (^) The distance travelled by a wave

each second

• (^) Wave speed is given the symbol, ν ,

and is measured in metres per

second (m/s), it can be calculated

using:

• (^) wave speed = frequency × wavelength