SPH4U1 - Waves and Light

Transcription

1 SPH4U1 - Waves and Light Multiple Choice (1 ark each) Identify the letter of the choice that best copletes the stateent or answers the question. 1. Consider the following wave properties with regard to diffraction: I. aplitude II. frequency III. wavelength IV. slit width V. source distance Which of the above can affect the aount of diffraction that occurs in a wave? a) I and V only d) III and IV only b) I, II, and III only e) II, III, IV, and V only c) II, III, and IV only 2. In a two-point source interference pattern in a ripple tank, a point is one wavelength farther fro one source than the other. If the two sources are in phase, then there is a) destructive interference at this point b) constructive interference at this point c) both constructive and destructive interference siultaneously d) neither constructive nor destructive interference at this point e) no interaction between the two waves at this point 3. Several experients are perfored with light. Which of the following observations is not consistent with the wave odel of light? a) The bea of light travels in a straight line. b) The speed of the light is less in water than in air. c) The light can exhibit interference patterns when travelling through sall openings. d) The light can be siultaneously reflected and transitted at certain interfaces. e) The light can travel through a vacuu. 4. Light ust travel as a transverse wave because it a) can be polarized b) can travel through a vacuu c) slows down and bends toward the noral d) undergoes diffraction e) disperses when travelling through a glass pris 5. Light fro a onochroatic source passes through a single slit and illuinates a screen. Which of the following patterns would best illustrate the interference pattern seen on the screen? a) d) b) e) c) 6. An experient using a diffraction grating with a onochroatic light source is perfored to create an interference pattern on a screen. Which of the following changes would cause the pattern to spread out? a) perfor the exact sae experient underwater b) use a grating that has a higher line density c) use a light source with a shorter wavelength d) ove the screen farther away e) both b. and d. Short Answer

2 1. Young s experient was instruental in supporting Huygens wave theory of light. Explain which two conditions Young satisfied in his experient that were not adequately done before. Describe how he achieved these two conditions. (2 arks) 2. The diagra shown below illustrates the possible paths followed by a light ray as it enters a lens (n = 1.56) covered with a thin coating (n = 1.25). If the thin coating has a thickness of, what type of interference occurs with rays 3 and 4? Explain your answer. (3 arks) Proble 1. A two-point source interference pattern is generated in a swiing pool. A piece of styrofoa, located on the second nodal line, is 12.0 fro one source and 20.0 fro the other source. One wave crest takes 2.0 s to travel the 35.0 width of the pool. Find the speed, wavelength, and frequency of the waves. (6 arks) 2. Blue light with a wavelength of 475 n is passed through a double slit with a separation of 22.6 µ. What is the axiu nuber of nodal lines visible in the entire pattern? (4 arks) 3. A single-slit interference pattern using blue light with a wavelength of 438 n creates a central axiu that is 6.50 c wide. If the slit width used is 17.5 µ, how far away is the screen? (4 arks) 4. A picture frae anufacturer wishes to design picture fraes that provide inial glare fro the glass cover. In order to achieve this, a thin plastic fil (n fil = 1.35) is placed on the glass surface (n glass = 1.52). If light reflected in the iddle of the visible spectru with a wavelength of 550 n is to be iniized, what fil thickness is required? (4 arks) 5. The thickness of a huan hair is to be easured using the interference pattern produced by an air wedge. Red light with a wavelength of 638 n is used on an air wedge that is 25.0 c long. If bright fringes are counted across 1.06 c in the air wedge, what is the thickness of the hair? (4 arks)

3 SPH4U1 - Waves and Light Answer Section MULTIPLE CHOICE 1. C 2. B 3. E 4. A 5. B 6. E SHORT ANSWER 1. - In order to see a stationary interference pattern, the phase of the two sources ust be constant, and the two narrow sources close together. - By using a single bulb and two very narrow pinholes placed close together, Young was able to satisfy both of these conditions, allowing a stationary diffraction pattern to be observed 2. Constructive interference occurs between the rays. Since ray 3 passes straight through, its phase is unchanged. Ray 4 is reflected fro a ore dense surface, so its phase is inverted when it reflects fro the lens surface, but not inverted when it reflects fro the air. Since ray 4 has travelled a total of half a wavelength farther, the two rays are in opposite phase; however, the extra inversion af wave 4 brings the back into phase. Hence, constructive interference occurs. PROBLEM 1.

4 2. The speed is 18 /s, the wavelength is 5.3, and the frequency is 3.3 Hz. The axiu nuber of nodal lines in the pattern is 96 (48 on each side of the central axiu).

5 3. The screen is 1.30 away. 4. The reflection fro the air-fil interface will be 180 out of phase with the incident light. The reflection fro the fil glass interface will also be 180 out of phase with the incident light. (Both reflections occur at a less dense to ore dense boundary.) Therefore, the two reflected rays would be in phase if the path difference were zero. To produce destructive interference between these two rays, and hence iniize the glare, the path difference ust be. To achieve this, the fil thickness ust be, where is the wavelength of the light in the fil.

6 To iniize the glare, the fil thickness should be L = 25.0c = 2.50 # fringes = # x' s = 9 9 x = 1.06c x = λ = 6.38 λl x = 2T 7 (6.38 )(2.5 T = 3 2(1.178 ) T = ) The thickness of the hair is 67.7 µ.