For the gray opaque surface having the spectral emissivity given in the figure, determine the spectral reflectivity.
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In an elastic collision between two bodies of mass m1 and m2, with m2 initially at rest, mass 1 moves off at angle ? relative to the direction of its initial velocity and mass 2 at angle ?. An exam paper shows the equations below: m1v1i 0 = m1v1f cos? + m2v2f sin? = m1v1f sin? + m2v2f cos? What error(s) has the student made?
a. In the first equation, m2v2f sin? should be m2v2f cos?. b. In the second equation, m2v2f cos? should be m2v2f sin?. c. In the second equation, the plus sign between the terms on the right should be a minus sign. d. All of the errors listed above. e. Only errors (a) and (b) above.
Neutron stars do NOT have:
A) masses greater than 1.4 solar masses. B) sizes comparable to large cities. C) strong magnetic fields. D) large surface gravities, compared to the Sun. E) rotation periods comparable to the Sun's.
The word LASER is an acronym for
A) Light Altered Spectra of Energy Radiated. B) Latent Source of Enhanced Radiation. C) Light Amplification by the Stimulated Emission of Radiation. D) Light Absorbed States of Energetic Resonance. E) none of the above answers.
An iron bolt is galvanized with a coating of zinc 0.03 cm (0.012 in) thick to protect the iron in a saltwater environment. The bolt has an area of 2 cm2 and is used to secure an iron plate with an area of 100 cm2 that is exposed to saltwater. In an experiment in seawater with a zinc coated iron anode of 2 cm2 and an iron plate cathode with an area of 100 cm2 a corrosion current of 2 mA is measured. Predict the expected lifetime in years or days of the zinc coating in this application assuming that the zinc coating is uniformly corroded and that the current efficiency is 100 %.
What will be an ideal response?