DIFFRACTION 05 MAY 2014

Transcription

1 IFFRTION 05 MY 2014 In this lesson we: Lesson escription Use Huygen s Principle to explain Show how the degree of is related to wavelength and the slit width Summary wavefront is an imaginary line joining all the points in a wave that are in phase. That is all the crests could be joined together to form a wavefront. iffraction is a wave property. Waves bend around the barrier or bend after passing through a slit or gap. Huygen s Principle states: ll points on a wavefront act like a source. Each one of these point sources (secondary sources) produces small circular waves moving forwards with the same speed as the waves. The new wavefront is obtained by drawing a tangent to all the new little wavefronts. Huygen s principle is very helpful in explaining. is defined as the phenomenon is which two waves superimpose to form a resultant wave of greater or lower amplitude. When two waves meet they can interfere with each other. This can be constructive or destructive. onstructive Waves & are in phase with each other. This means that a crest from wave will meet a crest from wave. When the two crests meet they interfere in such a way as so increase the total amplitude of the wave. The waves then move past each other and continue as they were before they met.

2 estructive Examples of iffraction 1. Water Waves Waves & are in out of phase with each other. This means that a crest from wave will meet a trough from wave. When the two crests meet they interfere in such a way as so decrease the total amplitude of the wave to zero The waves then move past each other and continue as they were before they met. 2. Light Effect of iffraction The amount of of a wave depends on the width of the slit in the barrier. When the slit is wide the is smaller, so the resulting wave is less circular. When the slit is narrow, then the is greater and the resulting wave is more circular. The amount of of a wave depends on the wavelength of the wave too. The maximum amount of occurs when the width of the slit is equal to the wavelength of the wave.

3 Question 1 Test Yourself Which wave property will be seen when a wavefront strikes a barrier? Question 2 Which wave property will be seen when a wavefront moves around the end of a barrier? Question 3 Which wave property will be seen when a wavefront moves through a small gap in a barrier? Question 4 Water waves with a wavelength of 0,5cm move towards a gap in a barrier that is 2cm wide. What will you observe in the water one the other side of the barrier? Question 5 straight wavefronts straight wavefronts with small curved sections on each end circular wavefronts no wavefronts Water waves with a wavelength of 0,5cm move towards a gap in a barrier that is 0,5cm wide. What will you observe in the water one the other side of the barrier? straight wavefronts straight wavefronts with small curved sections on each end circular wavefronts no wavefronts

4 Question 6 Water waves with a wavelength of 0,5cm move towards a gap in a barrier that is 0,5cm wide. The frequency of the source was increased while the speed of waves remained the same. What happens to the amount of? increases Question 7 stays the same decreases depends on the slit width Water waves with a wavelength of 0,5cm move towards a gap in a barrier that is 0,5cm wide. The width of the gap decreases. What happens to the amount of? increases Question 8 stays the same decreases depends on the wavelength beam of red laser light passes through a small slit. pattern appears on screen. large central band of red light directly opposite the gap is formed. What property can be used to describe this observation? destructive constructive particle nature of light Question 9 beam of red laser light passes through a small slit. pattern appears on screen. Two small dark bands appear next to the large central band of red light. What property can be used to describe the formation of these dark bands? destructive constructive Question 10 shadows from the edge of the slit beam of red laser light passes through a small slit. pattern appears on screen. If the red laser is replaced with a blue lazer light, you would notice more less the same amount of no pattern

5 Question 1 Improve your Skills onsider the following pattern observed when two water waves interfere with each other. The thick dark lines represent crests. What type of occurs at points, and? Explain your answer. Question 2 raw a sketch of a wavefront and use Huygen s principle to explain the following: a.) b.) c.) d.) Question 3 How a straight wavefront moves through the medium How a curved wavefront moves through a medium How a straight wavefront move past a barrier How a straight wavefront moves through a small gap Monochromatic blue light is shone through a very narrow single slit. When a screen is placed a sufficient distance away a pattern in observed. a.) b.) c.) d.) e.) escribe the pattern that is observed Give the name of the this phenomenon and define this phenomenon Name and state the principle can be used to explain this phenomenon Explain the bright bands observed. Predict what you would see if you used red light instead of blue light