Practice Exam Problems (Chapter 21)

Last updated: November 2, 2008 PHY 2054 Discussion – Fall ‘08 Practice Exam Problems (Chapter 21)

1. Maxwell developed his theory of electromagnetism by combining previous discoveries. He added his own original hypothesis that: (Maxwell’s Prediction) a. electric charges produce electric fields b. moving electric charges produce magnetic fields c. changing electric fields produce magnetic fields c. changing magnetic fields produce electric fields

2. A radar pulse returns 3.0×10-4 seconds after it is sent out, having been reflected by an object. What is the distance between the radar antenna and the object? (Speed of Electromagnetic Wave) a. 9.0×104 m b. 4.5×104 m c. 6.0×104 m d. 1.0×104 m

3. An ultraviolet light wave has a wavelength of 300 nm and speed of 2.1×108 m/s through a transparent medium. What is the frequency of this wave in the medium? (Wave Equation) a. 6.3×10 2 Hz b. 9.0×102 Hz c. 7.0×1014 Hz c. 10×1014 Hz

4. The Earth is 1.49×1011 m from the Sun. If the solar radiation at the top of the Earth’s atmosphere is 1 340 W/m2, what is the total power output of the Sun? (Intensity of Spherical Waves) a. 7.48×10 27 W b. 2.34×1030 W c. 6.62×1026 W d. 3.74×1026 W

5. In order of increasing frequency, which of the following is correct? (Spectrum of Electromagnetic Waves) a. visible, radio, ultraviolet and x-ray b. infrared, visible, ultraviolet and gamma c. visible, gamma, ultraviolet and x-ray d. infrared x-ray, visible and gamma

6. An observer is moving in space toward a distant star at 100 km/s while the star is moving toward the observer at 200 km/s; the relative velocity being 300 km/s of approach. What relative change in frequency of the light from the star as seen by the observer? (Doppler Effect) a. 0.10 % increase b. 0.10 % decrease c. 0.067% increase d. 0.033% decrease

Answers: 1-c 2-b 3-c 4-d 5-b 6-a