1) a hot, bright star would appear in which section of an h-r diagram ? a) lower left b) upper right c) upper left d) lower right 2) all stars remain on the main sequence a) until they stabilize b) for about 90% of their lifetimes c) until they become protostars d) for about 10 billion years

Answer 1) Option C) Upper Left

Explanation : Hertzsprung-Russell (or H-R) diagrams are a graphical tool used to classify the stars according to their brightness (luminosity), spectral type and hotness (temperature) . In this diagram the stars which are found to be hot and bright are placed on the top left upper corner. Stars which are in the stable phase of hydrogen burning lie along the Main Sequence according to their mass.

Answer 2) Option B) for about 90% of their lifetimes

Explanation : It is found that the main sequence stars spend their 90% of lifetime fusing hydrogen into helium. These main sequence stars burns the hydrogen present in its core, until it reaches the end of its life cycle. At this point, it leaves the main sequence.

Hence, It spends 90% of its lifetime in the main sequence.

increase masses, decrease separation

speed of light in vacuum is 300,000 km/s

speed of light in other mediums is given by the expression v = c/n, where c is the speed of light in vacuum and n is the refractive index of medium.

for the first medium v = 200,000 km/s

  so, refractive index of medium = 300000/200000 = 1.5

    1.5 refractive index is usually for glass. so first medium is glass.

for the second medium v = 250,00 km/s

so, refractive index of medium = 300000/250000 = 1.2

    1.2 refractive index is usually for water. so second medium is water.

for the third medium v = 0 km/s

so, refractive index of medium = 300000/0 = ∞

    ∞ refractive index is usually for opaque mediums. so third medium is opaque medium.