What causes auroras?
A. particles from the Sun colliding with and exciting atoms in our upper atmosphere
B. waves in the magnetic field creating an upper atmospheric laser-like effect
C. micro meteorites burning up as they sweep along Earth's magnetic field
D. fluorescence by upper atmospheric hydrogen atoms
E. sunlight reflected off meteor dust high in the atmosphere
Answer: A
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50) A 0.25-m string, vibrating in its sixth harmonic, excites a 0.96-m pipe that is open at both ends into its second overtone resonance. The speed of sound in air is 345 m/s. The common resonant frequency of the string and the pipe is closest to
A) 540 Hz. B) 360 Hz. C) 450 Hz. D) 630 Hz. E) 700 Hz.
Three resistors with values R1, R2 and R3, respectively, are connected in parallel. Which of the following expresses the total resistance, RT, of the three resistors when connected in parallel?
a. RT = R1 + R2 + R3 b. RT = (1/R1 + 1/R2 + 1/R3) c. RT = R1 = R2 = R3 d. RT = (1/R1 + 1/R2 + 1/R3)?1
A uniform solid sphere rolls without slipping along a horizontal surface. What fraction of its total kinetic energy is in the form of rotational kinetic energy about the CM?
Thermal neutrons are
A) neutrons that are hot. B) neutrons that are cold. C) neutrons with a kinetic energy of about 1/40 eV D) neutrons that are used for heating. E) neutrons that are used for cooling.