Measurement of Length

Convert $2$ angstrom into picometre.

"The definition of metre based on velocity of light is considered to be absolutely constant" why?

One Angstrom is equal to:

 In Fermi-Dirac Statistics, one energy state can be occupied by more than one particle.

To avoid the _____ error, while taking the measurements, the screw should be rotated in one direction only.

To avoid the backlash error, while taking the measurements, the screw should be rotated in one direction only.

Backlash error is observed that on reversing the direction of rotation of the thimble, the tip of the screw does not start moving in the opposite direction at once, but it remains stationary for a part of rotation.

How to avoid backlash error?

What is backlash error?

If the zero mark of circular scale above the base line of main scale, the screw gauge is said to be positive zero error.

If the zero mark of circular scale below the base line of main scale, the screw gauge is said to be positive zero error.

If the zero mark of circular scale coincides with the base line of main scale, the screw gauge is said to be free from zero error.

What is zero error of the screw gauge and how to identify the zero error?

The pitch of a screw is the distance moved along its axis by the screw in one complete rotation of its head.

Define the pitch of the screw gauge?

The pitch of a screw gauge is $0.5 \mathrm{mm}$ and the head scale is divided in $200$ parts. What is the least count of screw gauge?

What is zero error and types of zero errors in vernier scale?

The zero error is equal to the length between the zero mark of the main scale and the zero mark of the vernier scale.

A vernier callipers has its main scale graduated in $\mathrm{mm}$ and $10$ divisions on its vernier scale are equal in length to $9 \mathrm{mm}$. When the two jaws are in contact, the zero of vernier scale is ahead of zero of main scale and $4^{\mathrm{th}}$ division of vernier scale coincides with a main scale division. Find the zero error of the vernier callipers.

Figure given below shows the two scales of a vernier callipers. Find the least count.