2 Marks Questions

Question 12 Marks

What is the advantage of using a polygonal mirror with larger number of faces in Michelson method of measuring the speed of light?

Answer

The advantage of using a polygonal mirror with larger number of faces in the Michelson method is it gives the value that is very near to the accurate value and minimises the error.

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Question 22 Marks

In a Michelson experiment for measuring speed of light, the distance travelled by light between two reflections from the rotating mirror is $4.8\ km.$ The rotating mirror has a shape of a regular octagon. At what minimum angular speed of the mirror $($other than zero$)$ the image is formed at the position where a non$-$rotating mirror forms it?

Answer

In the given Michelson experiment, $D = 4.8\ km = 4.8 \times 10^3m \ N = 8$
We know, $\text{c}=\frac{\text{D}\omega\text{N}}{2\pi}$
$\Rightarrow\omega=\frac{2\pi\text{c}}{\text{DN}}\text{rad/sec}=\frac{\text{c}}{\text{DN}}\text{rev/ sec}$
$=\frac{3\times10^8}{4.8\times10^3\times8}$
$=7.8\times10^3\text{rev/sec}$

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