Name: Period: Date: Explain why the sound heard by the observer changes regularly. Determine the maximum frequency of the sound heard by the observer.

Transcription

1 Name: Period: Date: IB-2 Doppler Effect Practice 1. This question is about the Doppler effect. A stationary loudspeaker emits sound of frequency of 1000 Hz. Nadine attaches the loudspeaker to a string. She moves the loudspeaker in a horizontal circle above her head at a speed of 30 m s 1. The speed of sound in air is 330 m s 1. An observer is standing well away from Nadine. (a) Explain why the sound heard by the observer changes regularly. (b) Determine the maximum frequency of the sound heard by the observer. (Total 6 marks) 2. A man standing by the shore observes sea waves approaching at a frequency of 0.20 Hz. A man on a boat observes that waves are approaching the boat at a frequency of 0.50 Hz. The speed of the waves is 2.0 m s 1. Which of the following gives a possible value for the speed of the boat and its direction? Speed / m s 1 Direction A. 3.0 away from the shore B. 3.0 towards the shore C. 1.2 away from the shore D. 1.2 towards the shore

2 3. This question is about the Doppler effect. The wavelength diagram shown represents three lines in the emission spectrum sample of calcium in a laboratory. A distant star is known to be moving directly away from the Earth at a speed of 0.1c. The light emitted from the star contains the emission spectra of calcium. On the diagram sketch the emission spectrum of the star as observed in the laboratory. Label the lines that correspond to A, B, and C with the letters A*, B*, and C*. Numerical values of the wavelengths are not required. (Total 3 marks) 4. 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 IB Questionbank Physics 2

3 5. This question is about the Doppler effect. The sound emitted by a car s horn has frequency f, as measured by the driver. An observer moves towards the stationary car at constant speed and measures the frequency of the sound to be f. (a) Explain, using a diagram, any difference between f and f. (b) The frequency f is Hz. An observer moves towards the stationary car at a constant speed of 15.0 m s 1. Calculate the observed frequency f of the sound. The speed of sound in air is m s 1. (2) (Total 5 marks) 6. Which of the following wave phenomena is associated with blood flow measurements? A. Polarization B. Diffraction C. Refraction D. Doppler effect IB Questionbank Physics 3

4 7. 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. 8. 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. C. wavelength measured by the observer is smaller by a factor. v v s D. wavelength measured by the observer is greater by a factor. v v s IB Questionbank Physics 4

5 9. A radar speed gun is used to measure the speed of a car. The car is moving with speed v away from the gun. The radar emits microwaves of frequency f and speed c. Which of the following is the frequency of the microwaves measured at the gun after reflection by the car? 2v v 2v A. f + f B. f + f C. f f D. f v f c 10. 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 5