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6.10 An Application Example of Fundamental Laws: The Barlow Wheel

In this section, we review a case study demonstrating the practical application of electrical machines that we discussed. Peter Barlow invented the Barlow wheel in 1822 to demonstrate the principle of a homopolar electric motor. The star-shaped wheel pivots for rotation and has points that dip into liquid mercury, which is contained within a wooden base. During operation, a horseshoe magnet is positioned on the wooden base, with its poles embracing the wheel. The wheel then rotates when an electric current passes between the hub of the wheel and contacts the mercury.

Now we analyze the Barlow wheel's operation as a motor to ascertain its rotational speed expression.

练习题

Who invented the Barlow wheel and in what year?

A. Michael Faraday in 1821

B. Peter Barlow in 1822

C. Zénobe Gramme in 1871

D. Nikola Tesla in 1888

What is the primary function of the liquid mercury in the Barlow wheel apparatus?

A. To lubricate the rotation of the star-shaped wheel

B. To cool the wheel during high-speed operation

C. To serve as an electrical contact for current flow between the hub and the wheel points

D. To amplify the magnetic field from the horseshoe magnet

Which of the following are components of the Barlow wheel apparatus as described in the text?

A. Star-shaped wheel that pivots for rotation

B. Liquid mercury contained within a wooden base

C. A horseshoe magnet with poles embracing the wheel

D. A segmented commutator for switching current direction

E. An electromagnet excited by alternating current

The Barlow wheel was invented to generate electrical power for practical applications.

In the Barlow wheel, the horseshoe magnet is positioned with its poles embracing the wheel to provide the magnetic field necessary for motor operation.

In the Barlow wheel, electric current flows between the hub of the wheel and the mercury contacts to produce rotation.

The Barlow wheel was invented by Peter Barlow in ___ to demonstrate the principle of a homopolar electric motor.

The Barlow wheel demonstrates the operating principle of a ___ electric motor, which uses a constant magnetic field from a permanent magnet.

Explain how the Barlow wheel converts electrical energy into mechanical rotation.

The Barlow wheel uses a horseshoe permanent magnet rather than an electromagnet. Which of the following statements correctly compare these two approaches for creating magnetic fields in electrical machines?

A. Permanent magnets provide a constant magnetic field without requiring external power

B. Electromagnets allow the magnetic field strength to be controlled by adjusting the current

C. The Barlow wheel's permanent magnet provides fixed flux density, unlike electromagnets where flux density depends on magnetomotive force (MMF)

D. Permanent magnets are always superior to electromagnets in all electrical machine applications

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