Option G 4:Diffraction

Transcription

1 Name: Date: Option G 4:Diffraction 1. This question is about optical resolution. The two point sources shown in the diagram below (not to scale) emit light of the same frequency. The light is incident on a rectangular, narrow slit and after passing through the slit, is brought to a focus on the screen. A B light sources slit Source B is covered. screen Using the axes below, draw a sketch graph to show how the intensity I of the light from A varies with distance along the screen. Label the curve you have drawn A. I distance along the screen Source B is now uncovered. The images of A and B on the screen are just resolved. Using the same axes as in, draw a sketch graph to show how the intensity I of the light from B varies with distance along the screen. Label this curve B. (1) 1

2 The bright star Sirius A is accompanied by a much fainter star, Sirius B. The mean distance of the stars from Earth is m. Under ideal atmospheric conditions, a telescope with an objective lens of diameter 25 cm can just resolve the stars as two separate images. (c) Assuming that the average wavelength emitted by the stars is 500 nm, estimate the apparent, linear separation of the two stars. (3) (Total 6 marks) 2. This question is about single-slit diffraction. Explain, by reference to secondary wavelets, the diffraction of light at a single slit. Light from a helium-neon laser passes through a narrow slit and is incident on a screen 2.4 m distance from the slit. The graph below shows the variation with intensity I of the light on the screen of distance x along the screen. I x /mm 2

3 (i) The wavelength of the light emitted by the laser is 630 nm. Use data from the graph above to determine the width of the slit. (3) (ii) State two changes to the intensity distribution of the central maximum when the single slit is replaced by one of greater width (Total 7 marks) 3. This question is about a diffraction grating. Light of wavelength 590 nm is incident normally on a diffraction grating, as shown below. grating lines per metre light wavelength 590nm first order zero order first order The grating has lines per metre. Determine the total number of orders of diffracted light, including the zero order, that can be observed. (4) 3

4 The incident light is replaced by a beam of light consisting of two wavelengths, 590 nm and 589 nm. State two observable differences between a first order spectrum and a second order spectrum of the diffracted light (Total 6 marks) 4. This question is about interference and diffraction. Light from a laser is incident on two slits of equal width. After passing through the slits, the light is incident on a screen. The diagram below shows the intensity distribution of the light on the screen. The wavelength of the light from the laser is 633 nm and the angular separation of the bright fringes on the screen is rad. Calculate the separation of the slits. (3) Light from the laser is incident on many slits of the same width as the widths of the slits above. Draw, on the above diagram, a possible new intensity distribution of the light on the screen. 4

5 (c) The laser is replaced by a source of white light. Describe, if any, the changes to the fringes on the screen. (Total 7 marks) 5. Monochromatic parallel light is incident on two slits of equal width and close together. After passing through the slits, the light is brought to a focus on a screen. The diagram below shows the intensity distribution of the light on the screen. I A B distance along the screen Light from the same source is incident on many slits of the same width as the widths of the slits above. Draw on the above diagram, a possible new intensity distribution of the light on the screen between the points A and B on the screen. A parallel beam of light of wavelength 450 nm is incident at right angles on a diffraction grating. The slit spacing of the diffraction grating is m. Determine the angle between the central maximum and first order principal maximum formed by the grating. (Total 4 marks) 5

6 6. This question is about single slit diffraction. The diagram below shows an experimental arrangement for observing Fraunhofer diffraction by a single slit. After passing through the convex lens L 1, monochromatic light from a point source P is incident on a narrow, rectangular single slit. After passing through the slit the light is brought to a focus on the screen by the lens L 2. The point source P is at the focal point of the lens L 1. P X L L 1 2 single slit screen The point X on the screen is directly opposite the central point of the slit. Explain qualitatively how Huygens principle accounts for the phenomenon of single slit diffraction. Using the axes below draw a graph to show how the intensity of the pattern varies with distance along the screen. The point X on the screen is shown as a reference point. (This is a sketch graph; you do not need to add any numerical values.) (3) 6

7 intensity X distance along screen (c) In this experiment the light has a wavelength of 500 nm and the width of the central maximum of intensity on the screen is 10.0 mm. When light of unknown wavelength λ is used, the width of the central maximum of intensity is 13.0 mm. Determine the value of λ. The lens L 1 is now removed and another point source Q emitting light of the same wavelength as P (500 nm) is placed 5.0 mm from P and the two sources are arranged as shown below. P 5.0 mm Q 1.50 m b Single slit The distance between the sources and the slit is 1.50 m. 7

8 (d) (i) State the condition for the image of P and the image of Q formed on the screen to be just resolved. (1) (ii) Determine the minimum width b of the slit for the two images to be just resolved. (Total 10 marks) 8