Question

1 metre can be defined as:

• A. Distance travelled by light in $\frac{1}{299792458}s$ in vacuum.
• B. Distance travelled by light in $\frac{1}{439898458}s$ in vacuum.
• C. Distance travelled by light in $\frac{1}{399792458}s$ in vacuum.
• D. Distance travelled by light in $\frac{1}{254792458}s$ in vacuum.

Answer 1

The correct option is A

Distance travelled by light in $\frac{1}{299792458}s$ in vacuum.

The speed of light is constant throughout the vacuum. Hence it is a suitable standard and can be taken as reference for measurement of distance. The speed of light is $299792458m{s}^{-1}$ in a vacuum.
We know, $speed=\frac{distance}{time}\Rightarrow time=\frac{distance}{speed}$
Given, distance $=1m$
$\therefore time=\frac{1}{299792458}s$
i.e., One meter is the distance travelled by light in $\frac{1}{299792458}s$ in vacuum.