Re: Pinhole Digest #929 - 05/25/02

Date view Thread view Subject view Author view Attachment view

From: Mark Lawton (markslawton@hotmail.com)
Date: Sat May 25 2002 - 09:16:37 PDT 

Date: Sat, 25 May 2002 09:16:37 -0700
Subject: Re: Pinhole Digest #929 - 05/25/02
From: Mark Lawton <markslawton@hotmail.com>
Message-ID: <B91506F5.23F1%markslawton@hotmail.com>

Geoff,

You raise a good question:

If the limiting factor is the resistance of the bulb then what is the
distinction between a bulb/battery and a flash/capacitor.

The main factor is the voltage. Typical batteries are in the tens of volts.
I believe the voltage of the charged capacitor in a flash is 1000's of
volts.

The capacitor discharges exponentially. When time elasped = Resistance of
circuit * Capacitance ... the voltage will have dropped to 37% of it's
initial value. So, the resistance & capacitance combination is chosen by
the designers so that the flash of light corresponds to the shutter speed.

Does this help?

I can't say much about the nature of the internal resistance other than to
say the all materials have resistance. If the charge passes through the
metals energy will be lost to heat.

-Mark

> From: "Pinhole Listserv" <pinhole@exploratorium.edu>
> Date: Sat, 25 May 2002 00:20:01 -0700
> To: "Pinhole Listserv" <pinhole@exploratorium.edu>
> Subject: Pinhole Digest #929 - 05/25/02
>
> Subject: Re: pinhole battery questions
> From: "Geoff Ruth" <gruth@leadershiphigh.org>
> Date: Fri, 24 May 2002 10:31:57 -0700
>
> Algis,
>
> This is very helpful. I'm confused about the distinction between a
> capacitor and a battery: it sounded like from what you wrote that the
> limiting factor was the resistance of the light bulb and not the
> galvanic cell. So in a flash, wouldn't the difference be in the
> resistance within the flash bulb, and not the resistance within the
> battery/capacitor?
>
> I guess I am also confused about why a battery has its own internal
> resistance. We made galvanic cells using zinc and copper metals and
> solutions in class, and I couldn't identify what item was increasing
> resistance and decreasing discharge. What would that be, if we used
> really heavy gauge wire to connect the metals?
>
> Thanks again for your help!
>
> - Geoff

Date view Thread view Subject view Author view Attachment view

This archive was generated by hypermail 2.1.3 : Mon Aug 05 2002 - 09:21:42 PDT