Operating Principles of the NIST 4 Watt Balance Source

The video tutorial explains the concept of balancing forces, comparing gravitational and electromagnetic methods. It introduces the Watt balance, a device that measures mass indirectly by determining the strength of a magnetic field and the current through a coil. The Watt balance operates in two modes: velocity mode, which measures field strength, and weighing mode, which balances the weight of a test mass using electromagnetic force. NIST's design uses a wheel instead of a balance beam, with laser sensors and interferometry ensuring precise measurements.

What type of force does the Watt balance use to balance a mass?

• Electromagnetic force

• Gravitational force

• Frictional force

• Nuclear force

In Velocity Mode, what is the purpose of moving the coil through the magnetic field?

• To measure the weight of the coil

• To induce a voltage proportional to the field strength

• To create an upward force

• To generate heat

What happens when an electrical current is run through the coil in Weighing Mode?

• The coil stops moving

• The coil becomes a permanent magnet

• The coil generates heat

• The coil exerts an upward force

What is the role of laser sensors in the Watt balance setup?

• To track the coil's motion using interferometry

• To measure the weight of the test mass

• To generate the magnetic field

• To cool down the system

How is equilibrium achieved in the Weighing Mode of the Watt balance?

• By increasing the velocity of the coil

• By carefully adjusting the current to offset the test mass weight

• By changing the weight of the test mass

• By adjusting the magnetic field strength