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Why are there magnets around the DVD laser player? Answered


I just disassembled an old DVD player. The laser is 'suspended' between two fairly powerful small batteries. Any idea WHY the batteries are there?

The link below shows the laser and the magnets.
Video

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steveastrouk
steveastrouk

Best Answer 10 years ago

They are used to focus the laser

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kelseymh
kelseymh

Answer 10 years ago

I'm glad Frollard clarified your description, Steve! Otherwise, I would have posted something highly sarcastic about linear Maxwell's equations and the inability of magnetic fields to affect the propagation of light.

It does make a lot of sense to use non-mechanical actuators to adjust the laser position. Much faster response and tighter control.

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steveastrouk
steveastrouk

Answer 10 years ago

In the same spirit, I am honour bound to point out that moving a lens around has to count as mechanical actuation.....

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kelseymh
kelseymh

Answer 10 years ago

:-D Yeah, yeah. Though using a non-contact method (magnets) is generally better than gears and levers.

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kelseymh
kelseymh

Answer 10 years ago

Ah, stupid me, making the spherical cow approximation again.

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frollard
frollard

Answer 10 years ago

Yup, in conjunction with a small coil (electromagnet) the laser can be moved with insanely good precision - limited only by the accuracy of the circuit controlling the coil.

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lemonie
lemonie

10 years ago

magnets and coils of wire = movement. L

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steveastrouk
steveastrouk

Answer 10 years ago

Since we're on a picky kick today courtesy of Dr. K...magnets and coils = force. Movement is optional.

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lemonie
lemonie

Answer 10 years ago


level 3 pickyness:
magnets and energised coils.

L

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steveastrouk
steveastrouk

Answer 10 years ago

I'll see you and raise you to level 4. A shorted coil will also exhibit a force if moved.

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lemonie
lemonie

Answer 10 years ago


you excite it with the magnetic-field, so technically it would still be energised/excited?

L

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kelseymh
kelseymh

Answer 10 years ago

F = dp/dt = m dv/dt + v dm/dt. You could use force to change mass, but that's probably a lot more difficult than changing velocity :-)

Isn't pointless Talmudic debate fun?