How does the interstellar medium obscure our view of most of the galaxy?
A) The small mixture of dust grains in the interstellar medium absorbs visible light.
B) Dust reflects most light from distant regions of the galaxy back towards the source.
C) Hydrogen gas produces so much visible light that the interstellar medium is opaque, blocking our view of anything beyond it.
D) Molecules in the interstellar medium absorb all wavelengths of light.
E) all of the above
A
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The half-life of a radioactive element is the time it takes for:
A) half of the radioactive atoms to double themselves. B) half of the radioactive atoms to decay into isotopes. C) the radioactive atoms to increase by half of its initial quantity. D) the radioactive atoms to increase to 1.5 times of its initial quantity.
Which would have the lower average molecular kinetic energy?
(i) a sample of hydrogen gas, H2, at 0°C (ii) a sample of oxygen gas, O2, at 100° C
1.(i) 2.(ii) 3.They have the same average molecular kinetic energy. 4.It is impossible to tell.How have astronomers discovered planets orbiting a star beyond the Sun?
A. They can see the planet brighten as it passes in front of its parent star. B. They have bounced radar off them. C. They can be detected by the slight gravitational tug that they exert on their parent stars. D. So far, no planets have been discovered around any other stars.
An object moves in a direction parallel to its length with a velocity that approaches the velocity of light. The width of this object, as measured by a stationary observer,
A) approaches infinity. B) approaches zero. C) increases slightly. D) decreases slightly. E) does not change.