Question

The mean distance between the Earth and the Sun is referred to as one:
A. Light year
B. Fermi
C. Astronomical unit
D. Angstrom

Answer 1

Hint: Recall the definition of one astronomical unit. It is defined as roughly the distance between the Earth and the Sun.

Complete step by step answer:
The Astronomical Unit (symbolized as au or AU) is a measure of length, used usually in astronomy as the name suggests. It is the mean of the distance between the Earth and the Sun.
The absolute distance between the Earth and the Sun keeps on changing constantly since the Earth travels around the Sun in an elliptical orbit with the sun at one of its foci. The mean distance is found out by averaging the distance of the aphelion (position where Earth is farthest to the sun) and perihelion (position where the Earth is nearest to the Sun).
The value of 1 Astronomical unit is approximately 150 million kilometers. Thus,
$1au=1.5\times {{10}^{11}}m$
One light year is the distance travelled by light in a span of 1 earth year. It is equal to $9.46\times {{10}^{15}}m$.
One angstrom is equal to $10^{-10}$ m.
One Fermi is equal to $10^{-15}$ m.

Additional information:
Like the astronomical unit, there is another unit of length that is used in astronomy. It is usually used to measure distances outside our solar system. This unit is known as parsec (pc). Its value is 31 trillion kilometers or 210,000 astronomical units.

Note: Students must have a strong hold on the units and dimensions of various physical quantities since they form the basics of the subject. If not known properly, such knowledge-based questions can easily lead to the student not being able to attempt a quick and easy scoring question, or even worse to make a silly mistake in it and lose marks.
These kinds of questions give easy marks in less time in competitive exams and a student who can answer such questions will definitely have an edge over others.