Module 4 - Section 2 - Diffraction And Reflection Flashcards
What is diffraction ?
It is the way that waves spread out as they come through a narrow gap or go around obstacles - all waves diffract but its not easy to observe
What does the amount of diffraction depend on ?
The amount of diffraction depends on the size of the gap in comparison to the wavelength of the wave being diffracted
What can you sue to investigate diffraction and what is the practical ?
You can use a ripple tank to investigate diffraction:
1) Ripple tanks are shallow tanks of water that you can generate a wave in - and this is done by an oscillating paddle - which continually dips into the water and creates regular waves with straight, parallel wave fronts
2) Then objects are placed into the ripple tank to create a barrier with a gap in the middle of it - this is used to see diffraction
3) This gap can be varied to see the effects this has on how the waves spread through the tank - When the gap is a lot bigger than the wavelength, diffraction is unnoticeable - You get noticeable diffraction through a gap several wavelengths wide - but you get the most diffraction when the gap is the same size as the wavelength
But as the gap decreases the diffraction becomes more noticeable until the gap becomes too small and the water waves cannot pass through it anymore - the waves are then reflected back on themselves
What happens when sound waves pass through a doorway ?
The size of the gap and the wavelength are usually roughly equal so a lot of diffraction occurs - that’s why you have no trouble hearing someone through an open doorway
How can diffraction in light be shown as ?
Diffraction in light can be shown by shining a laser light through a very narrow slit onto a screen - you can alter the amount of diffraction by changing the width of the slit
What happens to a wave of there is an object in front of the wavefront and not just a gap ?
When a wave meets an obstacle then you get diffraction around the edges - behind the obstacle is a shadow and this is where the wave is blocked - the wider the obstacle is compared to the wavelength of the wave the less diffraction you get and so the longer the shadow
What happens when you shine light waves at a slit ?
If the wavelength of a light wave is roughly similar size to the aperture ( the size of the slit ) you get a diffraction pattern of light and dark fringes - the pattern has a bright central fringe with alternating dark and bright fringes on either side of it - the narrower the slit - the wider the diffraction pattern
What is reflection ?
Reflection means the wave is bounced back when it hits a boundary - the angle of incidence is equal to the angle of reflection
Where is the angle of reflection ?
it is between the direction of the reflected waves and the normal.
