A possible means for making an airplane radar-invisible is to coat the plane with an antireflective polymer. If radar waves have a wavelength of 6.00 cm, and the index of refraction of the polymer is n = 1.68, how thick would the coating be if a 180° phase change occurs at both surfaces?
a. 17.9 mm
b. 35.7 mm
c. 8.93 mm
d. 4.46 mm
e. 25.2 mm
c
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In an x-ray tube, high-speed electrons are slammed into a lead target, giving off x-rays. If the electrons are accelerated from rest through a potential difference of 160 000 volts, what speed do they have when they strike the target? (qe = 1.6 × 10^?19 C, me = 9.11 × 10^?31 kg, and c = 3.00 × 10^8 m/s)
a. 0.79c b. 0.65c c. 0.83c d. 0.49c e. 0.48c
Phase Angles: A 60.0-?F capacitor is in series with a 100-? resistor connected across an ac source of frequency 120 Hz. What is the phase angle?
A. -12.5° B. +12.5° C. -77.6° D. +77.6° E. 90.0°
The study of the origin, large-scale structure, and future of the universe is termed
Which of the following can actually escape a black hole?
A. visible light B. electrons C. very low energy radio waves D. very high energy gamma rays E. None of these choices is correct.