Question

For defining the standard metre, wavelength of which material is considered ?
1. Neon
2. Krypton
3. Helium
4. Xenon

Answer 1

Correct Answer - Option 2 : Krypton

Length

• The meter is the length of the path traveled by the light in a vacuum during a time interval of 1 / 299,792,458 of a second of light emitted from Krypton – 86.
• This has the effect of making the fundamental standard available to everyone.
• Since, 1983, One meter is defined as the distance traveled by light in a vacuum during  1 / 299,792,458 of a second.
• This effectively defines the speed of light as exactly 299 792 458 m/sec.
• For making calculation easy, we usually take the speed of light (c) as 3 × 10⁸ m/sec.
• The speed of light is different for different wavelengths or colors.