Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

Re: camera flash sound



I didn't know what causes this. Thank you! My dog finds it highly
irritating. He hears flash units that I can't hear, putting the frequencies
well above 12-14kHz.

Vickie

-----Original Message-----
From: John S. Denker [mailto:jsd@MONMOUTH.COM]
Sent: Wednesday, February 12, 2003 11:12 AM
To: PHYS-L@lists.nau.edu
Subject: Re: camera flash sound


Carl E. Mungan wrote:

As a camera flash charges up, one hears a whirr of increasing pitch.

Not on my camera, but I know what you mean.

What causes this? Is there enough stray inductance to cause some
oscillation and hence mechanical stress via a magnetic interaction

The inductance isn't what's stray. But yes,
it's a magnetic interaction with the inductor.

You've got a switching power supply.
Central to its operation is an inductor,
which is used to stuff charge onto a capacitor.

Ideally they would use a toroidal inductor, which
has no stray fields. But to cut costs they might
use an inductor with lots of stray fields. These
put a force proportional to B^2 on any magnetic
objects in the vicinity. And of course at those
frequencies any piece of metal will be diamagnetic
just due to its conductivity. Then assuming some
less-than-infinite rigidity, you've got a noisemaker.

As the output voltage ramps up, the "inertia" of
the current in the inductor is more quickly overcome,
so the thing has to cycle faster.

(vaguely light-bulb filament style)?

I don't know what that's alluding to.
It is prohibited for anyone to disclose, copy, distribute the contents of
this message. Benedictine University does not review, edit or censor
E-Mail communications sent out through their System. The University
maintains and enforces policies regarding the acceptable use of its
technology resources. All messages express views solely of the sender,
which are not to be attributed to Benedictine University, and may not be
copied or distributed without this disclaimer.