Using a Multimeter for Science Project

Reply

  #1  
Old 04-16-07, 09:50 AM
Member
Thread Starter
Join Date: Mar 2007
Posts: 6
Received 0 Votes on 0 Posts
Using a Multimeter for Science Project

Hi,

My son (read: with my help) is building a fruit battery (lemon, orange, etc) and inserting a piece of copper wire and a piece of steel wire (like a straightened-out paper clip) into the fruit and then using a multimeter to measure which fruit produces the most energy as measured by voltage.

So I purchased a $12 analog mutlimeter and just wondering how the heck do I actually hook up the red and black leads that are attached to the multimeter? Do I just make contact with the two wires, and if so, red to what and black to what?

BTW: are we even going to be able to measure this to a perceptible degree? E.g., I think the fruit is supposed to produce about 0.7 volts or so and the mutlimeter range is from 0 to 500 so I have my doubts...

We are open to any suggestions on the best way to do this. I can trade up the analog version for a digital if it makes a difference. Is there a different measure besides voltage that can be better measured for such a science project, without spending a ton, of course???

Thanks,

Joe
 
Sponsored Links
  #2  
Old 04-16-07, 10:53 AM
Member
Join Date: Mar 2007
Location: Norway
Posts: 281
Received 0 Votes on 0 Posts
Analog may give easier readings, but the range shold be 0-2.5 volts or so.
dsk
 

Last edited by DIYaddict; 04-16-07 at 11:33 AM. Reason: Removed unnecessary quote
  #3  
Old 04-16-07, 11:34 AM
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,944
Received 42 Votes on 40 Posts
> inserting a piece of copper wire and a piece of steel wire

You'll get a better reading using a copper and zinc plates or strips instead of a wire. The increased surface area will yield better results. You can get rolls of steel and copper perforated strapping in the plumbing section of the hardware store that should work well.

> how the heck do I actually hook up the red and black leads

Red to one of the metal strips, black to the other. It doesn't matter which. If the meter shows negative voltage, then reverse the black and red leads.

> are we even going to be able to measure this to a perceptible degree?

You might see a little bit of needle deflection with the analog meter, but a digital would probably produce more readable results in this case. Either meter can detect 1 volt, but you may not be able to notice it on the analog.

> Is there a different measure besides voltage

You could power a small flashlight bulb from the fruit battery. Look for a small pocket flashlight that only uses one AAA battery; the bulb should be designed to operate on 1.5V. Disassemble the flashlight and run wires from the fruit battery to the bulb holder -- I bet it will glow a little bit. I doubt a fruit battery can produce enough juice (ha ha) for a 12V automotive accessory lamp, but it would be something else inexpensive to try.
 
  #4  
Old 04-16-07, 11:41 AM
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,944
Received 42 Votes on 40 Posts
You could also put several fruit batteries in series to get a more readable voltage. If each fruit battery produces 0.7V, then two batteries would produce 1.4V, three 2.1V, etc.

To make series batteries, stick a copper and zinc plate in each fruit as if you were making individual batteries. Chain them together at the dissimilar metals like so:

copper--(lemon1)--zinc *wire* copper--(lemon2)--zinc *wire* copper--(lemon3)--zinc

Measure between the leftmost copper and rightmost zinc, and this should produce a 2.1V fruit battery which could power a flashlight bulb.
 
  #5  
Old 04-16-07, 11:47 AM
Member
Join Date: Sep 2000
Location: United States
Posts: 18,497
Received 0 Votes on 0 Posts
"using a multimeter to measure which fruit produces the most energy as measured by voltage".

This is not a valid scientific concept. You cannot measure energy production by measuring voltage--you can't even approximate it. For example, a car battery only produces 12 volts, but has a lot of energy. And even a small Van de Graaff generator produces 250,000 volts, but a miniscule amount of energy.

The fruit may not produce enough energy to light a bulb, but it might produce enough energy to make a small clock tick.
 
  #6  
Old 04-16-07, 01:34 PM
ray2047's Avatar
Group Moderator
Join Date: Mar 2006
Location: USA
Posts: 33,597
Received 13 Votes on 11 Posts
You might also want to do some research on galvanometers. He might be able to make one based on old fashioned pre twentieth century designs. IIRC my science correctly they are more sensitive to lower voltages. That might make it into a much more impressive science project.
 
  #7  
Old 04-16-07, 03:15 PM
Member
Join Date: Jan 2006
Location: Owen Sound Ontario Canada
Posts: 541
Received 0 Votes on 0 Posts
http://www.seed.slb.com/en/scictr/lab/fruit/index.htm
Interesting project you are doing.
The meter you bought might do the job or might not.
Digital meters are better for that but more expensive.
Do you have a neighbour or friend at work that you can borrow a digital meter from. Can you tell us the make and model of you multimeter so we can see how accurate it is and get back to you.
I think it is fantastic that you and your son are doing this project together.

One thing I want to say is that I have several millimeters and I hate them around large current. I am saying if you are not use to them do not play with them in 120 volt outlets. If the leads are wrong and connected to the outlet, bad things can happen. I have a Power Point Presentation that shows how dangerous it can be. I just want you and your son to know that measuring electricity in fruit and real electricity are 2 different things.

I suggest you Google the project and get ideas.
Anything you have questions about, let us know.
 
  #8  
Old 04-19-07, 12:03 PM
Member
Thread Starter
Join Date: Mar 2007
Posts: 6
Received 0 Votes on 0 Posts
Big Thank You to all who helped with the great advice. I did end up getting the digital mm...partly becuase the very next day a $35 version from Sears went on sale for $12 (nice mark up, eh???).

Anyway, the results are in:

Granny Smith Apple @ 0.92
Lemon @ 0.91
Grapefruit @ 0.85
Lime @ 0.85
Red Apple @ 0.83
Orange @ 0.82

These are the high voltage readings for each fruit, but they were all consistent within a 1/100 or two. We used a piece of copper from 12/2 wiring, plus steel from a cotter pin. We tested the mm against batteries to make sure it worked accurately enough and got a 9.5ish reading for a 9V battery and 1.6 for a AA battery listed at 1.5V, so maybe it was a little high.

My son had hypothesized that the lemon would win based on its acidity and juice content, but the sour granny smith apple apparently was ever more "sour" and was also quite juicy based on the juice that oozed out when we pricked it with the wires.

My son (4th grade) was most happy that it all worked and he really got into it. We might try lighting a flashlight using a serial circuit just for kicks.

Thanks again!
 
  #9  
Old 04-19-07, 12:11 PM
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,944
Received 42 Votes on 40 Posts
Glad to hear that it worked out well.
 
  #10  
Old 04-19-07, 12:45 PM
Member
Join Date: Sep 2003
Location: Central New York State
Posts: 13,973
Received 0 Votes on 0 Posts
"Granny Smith Apple @ 0.92
Lemon @ 0.91
Grapefruit @ 0.85
Lime @ 0.85
Red Apple @ 0.83
Orange @ 0.82"

0.92 WHAT? volts? millivolts? Something different?
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
Display Modes
 
Ask a Question
Question Title:
Description:
Your question will be posted in: