Magnetic Fields and Loudspeakers

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Questions and Answers

What is the primary difference between the radial field in a loudspeaker magnet and a current meter?

Loudspeaker magnets produce a stronger, more uniform radial field, whereas current meters produce a weaker, more fluctuating radial field.
The fields are the same, they are both radial but they are created by different mechanisms.
The loudspeaker magnet's radial field is designed to exert a force on a moving coil while the current meter's radial field is designed to exert a force on stationary charge carriers.
The radial field in a current meter is used to rotate a coil, while the radial field in a loudspeaker is used to vibrate a coil. (correct)

If a loudspeaker magnet is used without armatures, what shape will the magnetic field lines take, especially in the region inside the ring?

The field will be a uniform field with parallel lines pointing directly outwards from the ring.
The field will be a complex shape with no axis of symmetry and varying strength.
The field will be a series of concentric circles inside the ring aligned to the poles.
The field will be along a defined axis of symmetry from North to South, with field lines curving from the outer edge towards the center of the ring. (correct)

What is the purpose of soft iron keepers when storing magnets and why do they work?

Keepers add additional unpaired electrons, increasing the magnetic strength.
Keepers prevent temperature changes that might affect magnets.
Keepers form closed chains with the magnet's domains, canceling free poles and resisting demagnetization. (correct)
Keepers provide a barrier that prevents magnetic fields from interacting with other objects.

Which of the following actions is LEAST likely to demagnetize a permanent magnet?

Storing the magnet with another magnet. (D) Signup and view all the answers

Why do magnets weaken over time if not stored correctly?

The 'free' poles at the ends repel each other, causing domains to misalign. (B) Signup and view all the answers

How is a radial magnetic field primarily used within the construction of a loudspeaker?

It is used to interact with current in a coil attached to the cone, producing the force that moves the diaphragm. (D) Signup and view all the answers

How is a radial magnetic field used within the construction of a current meter?

To cause a pointer to move in proportion to the current through a coil. (B) Signup and view all the answers

Which of the following is NOT a method of demagnetizing a magnet?

Storing a magnet with a soft iron keeper. (B) Signup and view all the answers

Flashcards

Radial fields in current meters

In current meters, radial fields ensure that the needle deflects proportionally to the current, regardless of its position. This leads to consistent and accurate measurements.

Radial fields in loudspeakers

In loudspeakers, radial fields help to focus the magnetic force on the voice coil, maximizing its movement and efficiency. This leads to clear and powerful sound.

Soft iron keeper function

A soft iron keeper placed around a magnet helps to prevent its demagnetization by creating a closed magnetic circuit. This is similar to how closing an electrical circuit helps to maintain power flow.

Demagnetization by heat

Keeping a magnet at a high temperature can cause its magnetic domains to become misaligned, leading to a decrease in magnetic strength. This is similar to how heat can weaken a metal object.