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GCE JAN 2008 : AS 2 Waves and Photons

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Centre Number 71 Candidate Number ADVANCED SUBSIDIARY (AS) General Certificate of Education January 2008 Physics assessing Module 2: Waves and Photons ASY21 Assessment Unit AS 2 [ASY21] WEDNESDAY 16 JANUARY, AFTERNOON TIME 1 hour. INSTRUCTIONS TO CANDIDATES Write your Centre Number and Candidate Number in the spaces provided at the top of this page. Answer all seven questions. Write your answers in the spaces provided in this question paper. INFORMATION FOR CANDIDATES The total mark for this paper is 60. Quality of written communication will be assessed in question 4(b). Figures in brackets printed down the right-hand side of pages indicate the marks awarded to each question or part question. Your attention is drawn to the Data and Formulae Sheet which is inside this question paper. You may use an electronic calculator. For Examiner s use only Question Number 1 2 3 4 5 6 7 Total Marks ASY2W8 3961 Marks If you need the values of physical constants to answer any questions in this paper, they may be found on the Data and Formulae Sheet. Examiner Only Marks Remark Answer all seven questions. 1 (a) A travelling wave passes through a medium. Fig. 1.1 is a graph showing how the displacement s of a particle at a certain point in the medium varies with time t. s A O B C D t Fig. 1.1 Four measurements on the graph are lettered A, B, C and D. Table 1.1 lists a number of quantities associated with the wave. Some or all of these quantities are equal to the measurements represented by the letters in Fig. 1.1. Table 1.1 Quantity Letter Amplitude Frequency Wavelength Period (i) Complete Table 1.1 with the appropriate letter A, B, C, D or N (meaning not represented ). For example, if you think that the frequency is equal to C, write the letter C in the table. If you can t find any measurement on the graph equal to the frequency, write the letter N. [2] ASY2W8 3961 2 [Turn over (ii) If you have used the letter N against any quantity in Table 1.1, show carefully how that quantity may be obtained from the measurements A, B, C or D in Fig. 1.1, together with any relevant definition or equation. Write your answers in the spaces below. Use the symbol v for the speed of the wave through the medium. You may not need to use all the spaces provided. [4] Quantity: ___________ Examiner Only Marks Remark Measurement required: ___________ How obtained from measurement: ______________________________________________________ ______________________________________________________ Quantity: ___________ Measurement required: ___________ How obtained from measurement: ______________________________________________________ ______________________________________________________ Quantity: ___________ Measurement required: ___________ How obtained from measurement: ______________________________________________________ ______________________________________________________ (b) A quantity called the phase difference is used to describe the relative positions of two or more waves. State the value of the phase difference between two waves which are exactly out of phase. Give the unit in which you have quoted this value. Phase difference = ___________________ Unit: ___________________ ASY2W8 ASY2W8 3961 [2] 3 [Turn over 2 (a) (i) A ray of light in air strikes the surface of a medium of refractive index n at an angle of incidence i. Write down the equation relating n, i and the angle of refraction r. Examiner Only Marks Remark ___________________________________________________ [1] (ii) State the two conditions which must apply if a ray of light, incident on the boundary between two media, is to be totally internally reflected. Condition 1: ___________________________________________ ______________________________________________________ Condition 2: ___________________________________________ ___________________________________________________ [2] (b) Fig. 2.1 shows a prism, made of glass of refractive index 1.52. Each of the angles of the prism is 60.0 . A ray of light strikes the face AB at point P at an angle of incidence of 45.0 . After refraction at P, the ray crosses the prism to Q, where it is refracted out of the prism. A 60 45 Q P i r 60 60 B C Fig. 2.1 (i) Calculate the angle of refraction r of the ray after it enters the prism at P. Angle of refraction = _____________ ASY2W8 3961 4 [2] [Turn over (ii) The refracted ray crosses the prism, striking face AC at Q. Calculate the angle of incidence i of this ray on face AC. Hint: angle r + angle i = the angle of the prism. Angle i = _____________ Examiner Only Marks Remark [1] (iii) In (a)(ii) you stated two conditions for total internal reflection. Show that one of these conditions is not satisfied when the ray meets face AC, so that the ray does emerge from the prism. Show your working clearly. [2] (iv) Calculate the angle the prism. to the normal at which the ray emerges from = _____________ ASY2W8 3961 [2] 5 [Turn over 3 (a) (i) Your Data and Formulae Sheet quotes the lens equation Examiner Only Marks Remark 1/u + 1/v = 1/f In this equation, what do the symbols u and v represent? u: ____________________________________________________ v: ____________________________________________________ What type of lens would have a negative value of f ? ___________________________________________________ [2] (ii) State very briefly how you could distinguish practically between a real image and a virtual image. ______________________________________________________ ___________________________________________________ [1] (b) Fig. 3.1 is a set of axes labelled 1/u and 1/v respectively. The scale used for the 1/v axis is the same as that for the 1/u axis. 1/v 0 0 1/u Fig. 3.1 On the axes of Fig. 3.1, draw a graph of 1/v against 1/u for a converging lens. Describe how an accurate value of the focal length of the lens can be deduced from this graph. _________________________________________________________ _________________________________________________________ _______________________________________________________ [3] ASY2W8 3961 6 [Turn over (c) A stamp collector holds a lens of focal length +20.0 cm at a distance of 12.5 cm from a postage stamp in order to study lettering. Examiner Only Marks Remark Find the numerical value of the linear magnification of the lens when used in this way. Magnification: ______________________ ASY2W8 3961 7 [4] [Turn over In part (b) of this question you should answer in continuous prose. You will be assessed on the quality of your written communication. 4 Examiner Only Marks Remark (a) A student is asked to state the principle of superposition. The response is: When two waves meet, the resultant amplitude is the algebraic (or vector) sum of their separate amplitudes. (i) The student has confused amplitude with another quantity associated with the waves. What is this quantity? ___________________________________________________ [1] (ii) In any case, it is wrong to talk about an algebraic (or vector) sum of two amplitudes. Why? ___________________________________________________ [1] ASY2W8 3961 8 [Turn over (b) A student sets up a demonstration of interference using a Young s slits arrangement. He uses separate filament lamps, with a colour filter to obtain monochromatic light, behind each slit. However, he is disappointed when he cannot observe any sign of an interference pattern on the screen. He then tries a similar experiment with sound. He uses two separate loudspeakers as sources, fed from the same variable frequency supply, and a microphone as detector. He is pleased to find that this demonstration works. Examiner Only Marks Remark Explain why the demonstration with light does not work, but that with sound does. Suggest how the light experiment should be modified to produce a visible interference pattern. _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _______________________________________________________ [3] Quality of written communication ASY2W8 3961 [1] 9 [Turn over (c) (i) In a laboratory demonstration of the Young s slit experiment with light from a helium neon laser (wavelength 6.33 10 7 m), it is desired to have a fringe separation of 12 mm. Give suitable values of the following quantities in this demonstration. Show any calculation clearly. Examiner Only Marks Remark 1. Slit screen distance: ____________ m 2. Slit separation: ____________ mm [4] (ii) State one safety precaution to be taken in carrying out the demonstration in (c)(i). ___________________________________________________ [1] ASY2W8 3961 10 [Turn over 5 (a) Laser light of wavelength 6.33 10 7 m strikes a diffraction grating normally, as shown in Fig. 5.1. Examiner Only Marks Remark first order incident light zero order first order grating Fig. 5.1 The angle between the two first-order diffraction directions is 33.1 . (i) Show that the grating has 4500 lines per centimetre. [3] (ii) Find the number of orders on one side of the zero-order direction that can be observed. Number of orders = _______________ [3] (b) Crystals contain regularly-spaced planes of atoms. In the early twentieth century it was suggested that these planes might act like the lines of a diffraction grating, so that incident electromagnetc radiation would be scattered strongly in certain directions. However, when visible light is directed at a transparent crystal, no pattern of orders of diffraction, such as is obtained with a laboratory grating, is observed. Explain this. _________________________________________________________ _________________________________________________________ _______________________________________________________ [2] ASY2W8 3961 11 [Turn over 6 (a) The work function of a metal is the energy required to remove an electron from the surface of a metal. Examiner Only Marks Remark (i) Suggest why energy is needed to remove an electron from a metal. ______________________________________________________ ______________________________________________________ ___________________________________________________ [1] (ii) In photoelectric emission, the energy needed to remove the electron is provided by a photon. What is a photon? ______________________________________________________ ______________________________________________________ ___________________________________________________ [2] (b) Your Data and Formulae Sheet gives the photoelectric effect equation 1 mv 2 = hf hf0 2 max (i) State what the following quantities represent: 1 mv 2 ________________________________________________ 2 max hf ____________________________________________________ f0 __________________________________________________ [2] ASY2W8 3961 12 [Turn over 1 (ii) Fig. 6.1 is a set of axes labelled mv 2 and frequency. 2 max Examiner Only Marks Remark 1 mv 2 2 max 0 0 frequency Fig. 6.1 1 On Fig. 6.1, draw a graph showing how mv 2 depends on 2 max frequency for photoelectric emission from a metal. State how you would use the graph to determine the following quantities: The Planck constant _____________________________________ The work function of the metal ____________________________ ___________________________________________________ [3] ASY2W8 3961 13 [Turn over 7 (a) Some physical phenomena indicate that light behaves as a wave, but others suggest that it behaves like a stream of particles. To understand any given phenomenon, either the wave or the particle idea must be used, but not both. Examiner Only Marks Remark Table 7.1 lists a number of phenomena associated with light. Table 7.1 Phenomenon Wave explanation Particle explanation Diffraction Fluorescence Line spectra Polarisation Complete the Table by adding a tick to the appropriate column to show whether the phenomenon is best understood using the wave or the particle approach. [2] (b) Moving electrons have wave-like properties. The wavelength of a moving electron is called the de Broglie wavelength. (i) Show that the momentum of an electron that has been accelerated from rest through a potential difference of 150 V is 6.6 10 24 kg ms 1. [2] (ii) Calculate the de Broglie wavelength of the electron in (b) (i). Wavelength = ________________ m ASY2W8 3961 14 [1] [Turn over THIS IS THE END OF THE QUESTION PAPER S 9/07 302-072-1 GCE Physics (Advanced Subsidiary and Advanced) Data and Formulae Sheet Values of constants speed of light in a vacuum c = 3.00 108 m s 1 permeability of a vacuum 0 = 4 10 7 H m 1 permittivity of a vacuum 0 = 8.85 10 12 F m 1 1 = 8.99 109 F 1 m 4 0 ( ) elementary charge e = 1.60 10 19 C the Planck constant h = 6.63 10 34 J s unified atomic mass unit 1 u = 1.66 10 27 kg mass of electron me = 9.11 10 31 kg mass of proton mp = 1.67 10 27 kg molar gas constant R = 8.31 J K 1 mol 1 the Avogadro constant NA = 6.02 1023 mol 1 the Boltzmann constant k = 1.38 10 23 J K 1 gravitational constant G = 6.67 10 11 N m2 kg 2 acceleration of free fall on the Earth s surface g = 9.81 m s 2 electron volt 1 eV = 1.60 10 19 J ASY21INS ASY2W8 3961.02 USEFUL FORMULAE The following equations may be useful in answering some of the questions in the examination: Thermal physics Mechanics Momentum-impulse relation mv mu = Ft for a constant force Average kinetic energy of a molecule 1 m<c2> 2 Power P = Fv Kinetic theory pV = 1 Nm <c2> 3 Conservation of energy 1 mv 2 2 1 mu 2 = Fs 2 for a constant force Simple harmonic motion Displacement x = x0 cos t or x = x0 sin t Velocity v = x 0 2 x 2 Simple pendulum T = 2 l / g Loaded helical spring T = 2 m / k Medical physics Sound intensity level/dB = 10 lg10(I/I0) Sound intensity difference/dB = 10 lg10(I2/I1) Resolving power sin = / D Waves Capacitors Capacitors in parallel 11 1 1 = + + C C1 C 2 C 3 C = C1 + C2 + C3 Time constant = RC Capacitors in series Electromagnetism Magnetic flux density due to current in (i)i long straight (i)i solenoid B= (ii) long straight (i)i conductor B= 0NI l 0I 2 a Alternating currents A.c. generator E = E0 sin t = BAN sin t Particles and photons Two-slit interference = ay/d Diffraction grating d sin = n Lens formula Stress and Strain Hooke s law F = kx Strain energy E = <F > x (= 1 Fx = 1 kx 2 2 2 if Hooke s law is obeyed) Electricity Potential divider 3961.02 Vout = R1Vin/(R1 + R2) A = N A = A0e t t1 = 0.693/ 2 Photoelectric effect 1 mv2 = max 2 de Broglie equation 1/u + 1/v = 1/ f Radioactive decay Half life Light ASY2W8 = 3 kT 2 = h /p Particle Physics Nuclear radius 1 r = r0 A3 hf hf0

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Additional Info : Gce Physics January 2008 Assessment Unit AS 2, Module 2: Waves and Photons
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