λ = d If d is decreased then W is increased (inverse proportionality with λ and L constant).

Transcription

1 Saple Probles: WAVES: Interference. Consier the arrangeent for Young s ouble slit experients using onochroatic light. What effect woul ecreasing the istance between the two slits have on the istance between the centres of the bright bans? W If is ecrease then W is increase (inverse proportionality with λ an L constant).. White light is use to illuinate the ouble slits in Young s experient instea of onochroatic light. Describe what you woul expect to see on the screen. The overlapping in the centre of the interference pattern will be seen as white (ROYGBIV). Then as we ove out fro the centre a series of copleentary colours will appear. Note that a copleentary colour is the colour of all colours (ie white light) inus a particular colour. eg. Copleentary yellow is ROGBIV an appears ifferent fro yellow. You are given the forula: λ W L What oes each sybol in the forula represent? What is the situation that the equation escribes? Monochroatic light falling on two narrow slits 0. apart prouces an interference pattern on a screen.0 away with bright bans.0 apart. What is the wavelength of the onochroatic light an in which part of the visible spectru oes it lie? 0. -4, L, W -3 λ W λ (blue - green region) 3. What is the istance between the slits for a ouble slit arrangeent which, illuinate with yellow light of wavelength 6.0, prouces an interference pattern. away with bright bans 0.30 c apart?

2 L., W 0.30 c 3-3, λ 6.0 W Monochroatic light passes through two parallel slits 0.03c apart an then falls on a screen 0c further away. The first bright ban is 0.6c fro the centre of the interference pattern. Fin the wavelength of the light c 3-4, L., W 0. - W λ. λ Young s ouble slit experient. In a Young s ouble slit experient using soiu light, nine interference fringes were foun to occupy 3.6 when viewe through a icroeter eyepiece with an iage plane was 40 fro the slits. Calculate the separation of the slits, assuing the wavelength of soiu light to be -4. bans occupie 3.6 (9 fringes) L 40,?, λ, W 3.6 / 0.36 λl W When the soiu lap was replace by a white light source with a green filter, an the eyepiece ove 0 further fro the slits, five green fringes were foun to occupy.3 in the eyepiece. Fin the ean wavelength of the light passe by the filter. fringes (6W 3 ) L , λ?, W.3 /

3 λx W 3.8 λ 4. λ What is eant by the ter coherent light sources? Why are they necessary for interference effects to be observe with light an how are they prouce? Coherent sources have a constant phase relationship (sae λ) an better resolution if sae aplitue (sae intensity). Light is not norally coherent (except laser light). 7. In a Young s ouble-slit interferoeter, the separation of the slits is 0.. What is the ban with of the interference pattern prouce 0 c fro the slits? 0. L with re light of wavelength 700n W R λl 3 with blue light of wavelength 40n λl W B.

4 Saple Questions: WAVES: Diffraction. Light of wavelength.0 passes through two parallel slits an the falls on a screen 4.0 away. The bright bans of the interference pattern are foun to be.0c apart. Fin the istance between the slits. The sae two slits are now illuinate by light of a ifferent wavelength an it is foun that the fifth iniu for this light occurs at the sae point on the screen as the fourth iniu for the previous light. Fin the wavelength of the secon source of light. λx λx.0 4 W - W W 4 since W λ.λ 4.λ W 4. λ. λ 4 etres. A iffraction grating has lines per etre. Fin the angular sprea in the secon orer spectru between re light of wavelength 7.0 an violet light of wavelength 4.. for re sinθ 7.67 for violet sinθ Angular separation is A He-Ne gas laser which prouces onochroatic light of a known wavelength λ6.38 is use to calibrate a grating in a spectroscope. The first orer iffraction line is foun at an angle of 0 to the incient bea. How any lines per etre are there on the grating? sinθ sin etres sin0 so.4 lines/etre At what angle woul the secon orer iffraction line appear?

5 4. The re light fro three separate sources is ixe an passe through a iffraction grating of 3 lines per etre. The wavelengths of the three lines are: Hyrogen 6. Neon 6.0 Argon 6.97 Calculate the eviations for the first orer iffraction lines of each of these sources. for hyrogen 6.6 for neon 6.0 for argon Woul the lines be reaily iscernible as three separate lines?. Explain why no interference bans are observe when light fro two ajacent laps fall on a screen. Two sources are not coherent. The photons are prouce ranoly an there is not a constant phase relationship. 6. A bea of light is polarise by passing it through a piece of polaroi. In what way oes the polarise bea iffer fro the original non-polarise bea? The polarise bea has one of its planes of vibrations reove or filtere out where as the unpolarise bea has all planes of vibration present. 7. Describe how you woul use a isc of polarising aterial to show that irect sunlight is not polarise whereas iffuse light fro the blue sky is partially polarise. When a polarising filter is hel up to the blue sky an rotate there is a ecrease in intensity ue to the light fro the blue sky being partially polarise.