Biology project help

[digitalrain]

Hello, I just registered here, and I hope you can bear with my extreme lack of knowledge.
Basically my project is this: testing the germination of seeds exposed to an electrical current.

My setup is extremely simple, but I seem to have run into a problem. What I expected to do was simply run a current through a sheet-like conductive medium, with the seeds resting on top of that medium. So, I connected a power supply to the ends of a sheet of aluminum foil, and I'm not reading any voltage.

This is where my lack of knowledge should become blatantly obvious...I'm pretty much stuck as to what to do. In all honesty, I'm not sure I'm even going about this the right way, and perhaps this project was a little ambitious given my level of competence in the subject. Anyway, I'm using this power supply:https://www.allelectronics.com/cgi-bin/item/PS-637/480/5V_8A,_3.3V_4A,_2.5V_2A_POWER_SUPPLY_.html
and I've tested it with LED's to make sure it's functioning, and it seems to be.
Any help on this would be greatly appreciated, thanks.

 

[j.p.bill]

You may need to redefine your experiment. Seeds resting on top of a sheet of foil aren't likely to be affected by any current running through the foil. This is beside the point that you may not have set up a circuit that makes a conduction path for the current through the sheet of foil. If you want to continue with this approach, use a resistor in series with the foil to control the current. Otherwise, your supply may burn up.

As a suggestion, perhaps exposure to curent while growing might demonstrate more of an effect. Line a pot with foil as the outer conductor, and introduce current by means of a wire inserted into the center of the soil in the pot. Planr seeds around the center conductor. Use a wall transformer and resistors to limit current (which will vary somewhat depending on the hydration of the soil).

 

[ericgibbs]

hi digitalrain,

If you have connected the ends of the power supply to the ends of an aluminium sheet. [ dont how long, wide,thick ].
Its most likely that the resistance of the sheet is so low, that your meter is reading about zero volts from one end of the sheet to the other end.
Or the PSU has started current limiting ?.

You havn't said what current is flowing in the sheet, do you have a current limiting resistor in circuit ?.

I would suggest that you connect the meter, set for amps/milliamps in series with one of the leads from your psu and the sheet, measure the current.

What sort of 'field' did you want to create near the seeds?

EricG

 

[JimB]

As inferred by others, the resistance of a sheet of aluminium foil will be very low and unless you put a large current through it, you will be hard pushed to measure any voltage across the sheet.

OK lets assume we have a voltage of 10mV across our ali sheet which is 100mm long, the area which each seed is in contact with the sheet is say 1mm long, the seed will experience at most 10mV/100 = 100uV. Not very much!

I suggest that you plant the seeds in some soil, and put electrodes at the ends of the seed tray and pass the current between the electrodes.
This way the seeds are more likely to experience some electric current.

JimB

 

[dknguyen]

If you just place the seed on the foil, the seed has such high resistance and the foil has such low resistance (and electricity takes the path of least resistance) that absolutely no current will ever bother trying to go through the seed. It doesn't matter very much (I don't think) about the surface area of the seed.

You might want to change your experiment to the germination of seeds in the presence of an electromagnetic field which is somewhat more relevant. Unless you can find some kind of conductive medium (like some kind of oil or something that will pass electricity but also allow the seed to germinate.)

 

[dknguyen]

Assuming you know how to use an ammeter, LEDs are not lightbulbs. They act as essentialy short circuits. What you did was use blew up your LED and now it won't light up whether you connect it up properly.

You need a resistor in series with the LED to limit the current flowing through it. This can be the same resistor mentioned in the earlier posts that limits the current through your foil sot he foil won't act as a short-circuit. Two birds (short circuits) with one stone (resistor).

 

[digitalrain]

Yeah, I was having doubts about the seeds getting any current (the most electronics I've learned was in 12th grade physics....not much). I think I shall scrap the idea of the seeds resting on a conductive medium, and instead take the advice of planting them in soil, and lining a pot with electrodes. That sounds like a much better idea.

By the way, I'm really sorry about creating this same topic again. After I created this one, I didn't see it show up, so I waited a day, and made it again, only to see that this one was already up. I probably didn't read something in the ToS or something. Anyway, sorry about that.

 

[stevez]

Let me ask a couple of questions -

1. Do you want the seeds to germinate with electrical current flowing thru them? If that is the case you will need to arrange for current to be conducted into one end, so to speak, then out the other end.

2. Is your experiment such that you want the seeds to germinate while in the very strong magnetic field that one might expect to see close to a current carrying conductor? If that is the case then the foil idea is a good place to start - we just need to work on some of the details.

In either case we'll need to be able to control the flow of current. Levels of current are likely to be very low or you'll roast rather than germinate the seeds. Sounds like an interesting experiment.

 

[digitalrain]

"2. Is your experiment such that you want the seeds to germinate while in the very strong magnetic field that one might expect to see close to a current carrying conductor? If that is the case then the foil idea is a good place to start - we just need to work on some of the details."

Yeah, that's pretty much what I was getting at, only I wasn't sure if that was a plausible idea. If you have any suggestions as to the setup regarding that I would really appreciate it.

 

[AllVol]

while in the very strong magnetic field that one might expect to see close to a current carrying conductor?

...was my first thought in connection with the experiment, yet that would involve the use of AC.

 

[Nigel Goodwin]

...was my first thought in connection with the experiment, yet that would involve the use of AC.

Why?, you get a magnetic field with DC as well.

 

[AllVol]

Why?, you get a magnetic field with DC as well.

Whoops! Musta been an Altizer's moment. Put me down for one in the BRaaaacccckkkk! (Wrong answer) column.

 

[digitalrain]

Well, what about a setup where I have coils wrapped around the seeds. Would that not create a electromagnetic field? I'll have to bring out my physics book for the equations to calculate the strength of the field though, I've forgot most of them.
How tightly would the coils need to be wrapped to create a strong enough field..of course that would depend on the type of seed and the conditions under which it's growing, but any rough estimates?
If there are other ways to produce a decent magnetic field, I'm open to those too. Thanks

 

[Hero999]

If you want to produce a magnetic field then permanent magnets are much better than a coil.

 

[Gaston]

but wouldn't an ac macgnetic feild induce a curent in the seed?however slight. i would say since its and experement. try ac and dc

 

[digitalrain]

Well, if possible, I'd like to stick with DC. I'd like to limit the variables as much as possible, since the experimental factor is simply whether it's in an electromagnetic field or not. I'm still kind of contemplating the setup though. I wonder if I should grow them in soil, or some other medium. I also have to take into account the amount of heat that could possibly be produced, and find a way to dissipate it so it doesn't confound the results.

 

[Hero999]

An electromagnetic field is exactly the same as a permanent magnetic field; the only difference is you can control and continuously vary the latter and not the former.