1. This question is about microwaves.

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1 1. This question is about microwaves. (a) Radiation from a microwave transmitter passes through a single narrow slit. A receiver is placed several metres beyond the slit. The receiver can be moved between point A and point B along a line parallel to the slit. (i) On the axes below, sketch a graph to show the variation of intensity of the microwave radiation with distance along line AB. The graph has been started for you. (3) IB Questionbank Physics 1

2 (ii) The width of the narrow slit is reduced. State and explain two effects on the intensity distribution you have shown in (a)(i). Effect:... Explanation:... Effect:... Explanation:... (4) (b) Standing waves are formed in microwave ovens. Suggest why it is desirable that food is rotated while being cooked in the microwave. (3) (Total 10 marks) IB Questionbank Physics 2

3 2. A source of sound approaches a stationary observer. The speed of the emitted sound and its wavelength, measured at the source, are v and λ respectively. Which of the following is the wave speed and the wavelength, as measured by the stationary observer? Wave speed Wavelength A. larger than v larger than λ B. equal to v larger than λ C. equal to v less than λ D. larger than v less than λ 3. This question is about microwave radiation. A microwave transmitter emits radiation of a single wavelength towards a metal plate along a line normal to the plate. The radiation is reflected back towards the transmitter. A microwave detector is moved along a line normal to the microwave transmitter and the metal plate. The detector records a sequence of equally spaced maxima and minima of intensity. (a) Explain how these maxima and minima are formed. (4) IB Questionbank Physics 3

4 (b) The microwave detector is moved through 130 mm from one point of minimum intensity to another point of minimum intensity. On the way it passes through nine points of maximum intensity. Calculate the (i) wavelength of the microwaves. (2) (ii) frequency of the microwaves. (2) IB Questionbank Physics 4

5 (c) Describe and explain how it could be demonstrated that the microwaves are polarized. (3) (Total 11 marks) 4. The wavelength of a standing (stationary) wave is equal to A. the distance between adjacent nodes. B. twice the distance between adjacent nodes. C. half the distance between adjacent nodes. D. the distance between a node and an adjacent antinode. IB Questionbank Physics 5

6 5. During a journey an observer travels at constant speed towards, and then goes beyond, a stationary emitter of sound. The frequency of the sound as measured at the emitter is f. The frequency according to the observer A. is always greater than f. B. is always equal to f. C. is always less than f. D. varies during the journey. 6. A parallel beam of monochromatic light of wavelength λ passes through a slit of width b. After passing through the slit the light is incident on a distant screen. The angular width of the central maximum is λ A. 2 radians. b λ B. radians. b λ C. 2 degrees. b λ D. degrees. b IB Questionbank Physics 6

7 7. Unpolarized light is shone through two identical polarizers whose axes are parallel. The ratio I I 0 is A. 100 %. B. 50 %. C. 25 %. D. 0 %. IB Questionbank Physics 7

8 8. This question is about diffraction and resolution. (a) Plane wavefronts of monochromatic light of wavelength λ are incident on a narrow slit. After passing through the slit they are incident on a screen placed a large distance from the slit. The width of the slit is b and the point X is at the centre of the slit. The point M on the screen is the position of the first minimum of the diffraction pattern formed on the screen. The path difference between light from the top edge of the slit and light from the bottom edge of the slit is l. Use the diagram to explain why the distance l is equal to λ. (3) IB Questionbank Physics 8

9 The wavefronts in (a) are from a monochromatic point source S 1. Diagram 1 is a sketch of how the intensity of the diffraction pattern formed by the single slit varies with angle θ. The units on the vertical axis are arbitary. Diagram 1 Another identical point source S 2 is placed close to S 1 as shown in diagram 2. Diagram 2 (b) The diffraction patterns formed by each source are just resolved. On diagram 1 sketch the intensity distribution of the light from source S 2. (2) IB Questionbank Physics 9

10 (c) Outline how the Rayleigh criterion affects the design of radio telescopes. (2) (d) The dish of the Arecibo radio telescope has a diameter of 300 m. Two distant radio sources are m apart. The sources are m from Earth and they emit radio waves of wavelength 21 cm. Determine whether the radio telescope can resolve these sources. (3) (Total 10 marks) 9. Which of the following statements is true for a standing wave on a string? A. No energy is transferred along the string. B. The maximum kinetic energy of each segment of the string is proportional to the amplitude of the segment. C. Each segment of the string oscillates with different phase and frequency. D. The amplitude along the string varies with time. IB Questionbank Physics 10

11 10. A siren at rest emits a sound of frequency f 0. The speed of sound in air is v. The siren moves away from an observer at rest relative to the siren in a straight line with constant speed v s. The observer measures a frequency lower than f 0 because the A. speed at which the sound moves relative to the observer is v v s. B. speed at which the sound moves relative to the observer is v s v. v C. wavelength measured by the observer is smaller by a factor s. v v D. wavelength measured by the observer is greater by a factor s. v 11. In an electron microscope, high energy electrons are used in order to increase the A. interference effects. B. diffraction effects. C. resolving power of the microscope. D. magnifying power of the microscope. IB Questionbank Physics 11

12 12. The diagram represents a beam of unpolarized light incident on a diamond. The refractive index of the diamond is n. At an angle θ p, the beam reflected from the diamond is plane polarized normal to the page. The angle θ p is A. tan 1 n. B. tan 1 1. n C. sin 1 1. n D. cos 1 1. n IB Questionbank Physics 12

13 13. Two polarizing sheets have planes of polarization that are initially parallel. The incoming light on sheet 1 is unpolarized. The intensity of the light transmitted is I. To I reduce the intensity to, which sheet must be rotated and through what angle? 2 Sheet to be rotated Rotation angle A. 1 only θ = cos B. 2 only θ = cos C. 1 or 2 θ = cos D. 1 or 2 θ = cos This question is about the diffraction of light. (a) (i) Describe what is meant by the diffraction of light. (2) IB Questionbank Physics 13

14 (ii) A parallel beam of monochromatic light from a laser is incident on a narrow slit. The diffracted light emerging from the slit is incident on a screen. (not to scale) The centre of the diffraction pattern produced on the screen is at C. On the axes sketch a graph to show how the intensity I of the light on the screen varies with the distance d from C. (3) (iii) The slit width is 0.40 mm and it is 1.9 m from the screen. The wavelength of the light is 620 nm. Determine the width of the central maximum on the screen. (3) IB Questionbank Physics 14

15 (b) (i) When two separate lasers are used as sources, the images of the slit formed by the light from each laser are resolved. State what is meant by the term resolved in this context. (1) (ii) A car, with its two headlights switched on, is approaching an observer who has good eyesight. Outline why, at a long distance from the observer, the images of the headlights of the car are not resolved by the observer. (4) (Total 13 marks) IB Questionbank Physics 15

16 15. Which of the following is a correct comparison between standing waves and travelling waves? Standing waves A. wave amplitude is constant at all points along the wave Travelling waves wave amplitude depends upon the position along the wave B. energy is always transferred energy is not transferred C. the wavelength is twice the distance between consecutive nodes D. phase varies continuously along the wave the wavelength is the distance between consecutive crests phase is constant between consecutive crests 16. Two galaxies with an angular separation at the observer of radians are observed with a radio telescope. Both galaxies emit radio waves of wavelength m. The images of the galaxies are just resolved by the telescope. The diameter of the circular collecting dish of the telescope is A. 61 m. B. 50 m. C. 30 m. D. 25 m. IB Questionbank Physics 16

17 17. The diagram shows sunlight reflected from a lake surface. The reflected sunlight is plane-polarized. The plane of polarization of the reflected sunlight is A. parallel to the lake surface. B. perpendicular to the lake surface. C. parallel to the direction of the reflected sunlight. D. in the plane of the diagram. IB Questionbank Physics 17

18 18. A tube is filled with water and a vibrating tuning fork is held above its open end. The tap at the base of the tube is opened. As the water runs out, the sound is loudest when the water level is a distance x below the top of the tube. A second loud sound is heard when the water level is a distance y below the top. Which of the following is a correct expression for the wavelength λ of the sound produced by the tuning fork? A. λ = y B. λ = 2x C. λ = y x D. λ = 2(y x) IB Questionbank Physics 18

19 19. A source S, moving at constant speed, emits a sound of constant frequency. The source passes by a stationary observer O, as shown below. Which of the following shows the variation with time t of the frequency f observed at O as the source S approaches and passes by the observer? IB Questionbank Physics 19

20 20. Unpolarized light of intensity I 0 is incident on a polarizer. The transmitted light is then incident on a second polarizer. The axis of the second polarizer makes an angle of 60 to the axis of the first polarizer. The cosine of 60 is A. I The intensity of the light transmitted through the second polarizer is I B I C I D Two binary stars emit radio waves of wavelength m. The waves are received by a radio telescope whose collecting dish has a diameter of 120 m. The two stars are just resolved if their minimum angular separation in radians is of the order of A B C D IB Questionbank Physics 20

21 22. 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) Point source B is covered. Using the axes below, sketch a graph to show how the intensity I of the light from point source A varies with distance along the screen. Label the curve you have drawn A. (2) (b) Point source B is now uncovered. The images of A and B on the screen are just resolved. Using the axes above, sketch a graph to show how the intensity I of the light from point source B varies with distance along the screen. Label this curve B. (1) IB Questionbank Physics 21

22 (c) 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. 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) 23. This question is about polarization and liquid crystals. (a) A liquid crystal has the property of being able to rotate the plane of polarization of light. Explain what is meant by the expression able to rotate the plane of polarization of light (2) IB Questionbank Physics 22

23 (b) The diagram below is a representation of a liquid crystal display. P 1 is a polarizer and P 2 is an analyser. The transmission axis of P 2 is at right angles to that of P 1. E is an electrode. G is a glass plate upon which a shaped electrode is etched. Unpolarized light is incident on P 1. (i) State, and explain, what the observer would see if the liquid crystal were not present (2) (ii) Outline how the application of a potential difference between E and the electrode etched on G enables the observer to see the shape of the electrode (3) (Total 7 marks) IB Questionbank Physics 23