Physics, 15.10.2019 06:30 CeddHendrix

With the discovery of dark energy, what best defines critical density?

a) the correct amount of matter and energy to make the universe flat.

b) the density of dark energy needed to accelerate the universe's expansion.

c) the amount of matter needed to counteract dark energy.

d) the amount of matter and energy needed to hold galaxies together

Answers: 3

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The correct answer is A. According to the Friedmann Equations, critical density is the correct amount of matter and energy to make the universe flat.

Explanation:

In cosmology, the critical density is the energy density for which space-time is flat on a large scale. In other words, the critical density is the energy density for which the spatial curvature of a homogeneous, isotropic and expanding universe is zero.

The critical density of the Universe expresses the density that discriminates the closed universe from the open one, that is to say between the one dominated by gravity (density greater than the critical one) by the one dominated by the expansion (density lower than the critical one).

Answer from: Quest

scattering of light by tiny particles in air to produce the colors we see on sky, is dependent on the following factors:

(i) wavelength of light

(ii) size of the scattering particle

(iii) distance traveled by light through the atmosphere.

according to rayleigh's law of scattering, the amount of scattering is inversely proportional to the fourth power of its wavelength. shorter the wavelength, greater is its scattering. hence violet/blue light is scattered more than red.

sun's light is a composite light ( visible light) with wavelengths in the range 400 nm (violet) to 700 nm (red). as sunlight passes through our atmosphere, the molecules of air scatter light according to their wavelengths. during sunrise and sunset, the sun's position is below the horizon. hence light from the sun travels a greater distance in the atmosphere when compared to its position a noon.

as sunlight enters the earth's atmosphere, blue light is scattered away and at the end of its journey in the sky, only red and orange wavelengths remain in the beam.

hence at sunrise and sunset, the sky appears reddish orange.

Answer from: Quest

Answer: it will take 4.36 seconds to reach her average velocity 10.69 miles/hour.explanation: we have equation of motion $s=ut+\frac{1}{2} at^2$ ,where s is the displacement, a is the acceleration, u is the initial velocity and t is the time taken.average velocity = displacement/ time taken.average velocity = 10.69 miles/hr = 10.69*1.6*1000/(60*60) = 4.75 m/s4.75 = s/ts = 4. 1we also have acceleration = 2.18 m/s², initial velocity = 0 m/s $s=0*t+\frac{1}{2} *2.18*t^2$ $s=1.09t^2[/ 2equating equation 1 and 2 [tex]4.75t = 1.09t^2\\ \\ t=4.36 seconds.$ so it will take 4.36 seconds to reach her average velocity 10.69 miles/hour.

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With the discovery of dark energy, what best defines critical density?

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