Help with some current and circuit concepts for Physics Question

TSOW

Basically we were given a physics question imagining a Professor demonstrating the ffects of current on the body.

A man has his hands 1.25m apart on a thin uninsulated current carrying cable.
Connected to conductor with max 6 Amps so that the potential difference between hands is not greater than 1.5 V.

My question is what ways are there to increase the current or voltage (not allowed to wet it) where it would reach the point that he would not be able to let go of the wire?
I'm just looking for help with the concepts.

If you need extra information I can elaborate...Thanks!

TSOW

Also, is there a way to make the voltage greater than 1.5 V without exceeding the 8 Amps?

TSOW

Anyone?

TSOW

Would cutting the cable help?

TSOW

Please help

TSOW

Also I meant 6 Amps...I can't edit my posts for some reason...

biketard

I'm not sure I understand the current (excuse the pun) setup. What/where is the power source at the moment? Can you draw a picture?

TSOW

biketard wrote: »

I'm not sure I understand the current (excuse the pun) setup. What/where is the power source at the moment? Can you draw a picture?

Sorry, I wasn't very clear, but my web is bugged so it's hard to edit.
The cable is the conductor and it's been set to have a current of 8 Amps. The power can't be altered, so I think it must be some alteration to the cable...just not sure what.

TSOW

I--O--I
P---H

---

H---


So P is the power source,
H = Hands

I, O attempts at arms and a head.

TSOW

biketard wrote: »

I'm not sure I understand the current (excuse the pun) setup. What/where is the power source at the moment? Can you draw a picture?

Also lol.

biketard

So after the cable passes your hands it then goes around and connects to the other side of the power source, right? (Just need to make sure.)

You say the power source is limited to 6 amps, but not what voltage it is. Are you getting the 1.5v potential difference purely from the distance between the hands and the 6 amps limit?

How about voltage passing through the body to ground? Is that taken into consideration at all, or should we assume that the body is completely isolated from the ground?

biketard

I think I'm SORT OF starting to understand the question. Undoubtedly cutting the cable would help (assuming the person is isolated from the ground). At the moment if the cable has less resistance that the person's body, then most or all of the current would go through that. Current will take the path of least resistance (literally in this case).

When you say "increase the current" you mean through the person's body, right?

TSOW

biketard wrote: »

So after the cable passes your hands it then goes around and connects to the other side of the power source, right? (Just need to make sure.)

You say the power source is limited to 6 amps, but not what voltage it is. Are you getting the 1.5v potential difference purely from the distance between the hands and the 6 amps limit?

How about voltage passing through the body to ground? Is that taken into consideration at all, or should we assume that the body is completely isolated from the ground?

Yes, it returns to the power source.

The 1.5 V is just from the distance and the Amps.
I think grounding can be taken into consideration.

TSOW

biketard wrote: »

I think I'm SORT OF starting to understand the question. Undoubtedly cutting the cable would help (assuming the person is isolated from the ground). At the moment if the cable has less resistance that the person's body, then most or all of the current would go through that. Current will take the path of least resistance (literally in this case).

When you say "increase the current" you mean through the person's body, right?

Yes..it is a weird question. We are basically being challenged to cause him to inflicted with a current of around 15 milliamps.

TSOW

Also parallel circuits was a term thrown around in class, not sure how helpful that could be. Is the overall resistance of the circuit lowered, because I was getting weird results assuming the man had a resistance of 10,000 Ohms and assuming a copper wire with a certain cross sectional diameter that gave 2.1 Ohms resistance where the total resistance was only 2.099 Ohms.

biketard

Well you'd need to work out the resistance of his body (R) from one hand to the other. Assuming he has to keep both hands 1.25m apart, then that's going to be a fixed value once you work it out. You already know that you need the current (I) to be 15 milliamps, so you basically have to up the voltage so that V=IR.

Of course you have to have cut that wire between his hands too.

TSOW

biketard wrote: »

Well you'd need to work out the resistance of his body (R) from one hand to the other. Assuming he has to keep both hands 1.25m apart, then that's going to be a fixed value once you work it out. You already know that you need the current (I) to be 15 milliamps, so you basically have to up the voltage so that V=IR.

Of course you have to have cut that wire between his hands too.

So, I guess if the wire was cut he would be in series and it would just be a matter or R1+R2, unless I count him as one big resistor.
Of course he would probably notice the cut wire...anything more inconspicuous? If not it's fine, any help is good at this point.

biketard

I assume the parallel circuit is referring to two resistors in parallel. One would be his body and the other would be the wire. As I said, the current will take the path of least resistance, or rather it will share the load between resistances. If the guy's body had the same resistance as the cable, then half of the current would go through him and the other half would go through the cable. If his body had a lot more resistance than the cable (undoubtedly the case here), then most of the current would go through the cable (again, I'm assuming he's isolated from the ground, which your teacher should've been specific about).

Cutting the cable will direct ALL of the current through his body, since there's no other route now.

Does that make sense?

This might help: http://www.regentsprep.org/regents/physics/phys03/bparcir/

TSOW

biketard wrote: »

I assume the parallel circuit is referring to two resistors in parallel. One would be his body and the other would be the wire. As I said, the current will take the path of least resistance, or rather it will share the load between resistances. If the guy's body had the same resistance as the cable, then half of the current would go through him and the other half would go through the cable. If his body had a lot more resistance than the cable (undoubtedly the case here), then most of the current would go through the cable (again, I'm assuming he's isolated from the ground, which your teacher should've been specific about).

Cutting the cable will direct ALL of the current through his body, since there's no other route now.

Does that make sense?

This might help:

Oh I see. I think given the circumstances that's probably the only thing that'll make sense.
When you say isolated from the ground, you mean that he is floating/electricity is blocked from reaching the ground (Rubber shoes or whatnot)?

biketard

TSOW wrote: »

So, I guess if the wire was cut he would be in series and it would just be a matter or R1+R2, unless I count him as one big resistor.
Of course he would probably notice the cut wire...anything more inconspicuous? If not it's fine, any help is good at this point.

Yes, you could also keep the wire intact and increase the voltage until the guy's share of the current still amounted to 15mA. It would require a bit more working out and would be a serious waste of electricity, but assuming the cable had SOME resistance, and could handle currents large enough to still give the guy his 40mA, it would work.

Is he not supposed to notice or something?

Are you allowed to swap out the wire for one with more resistance?

biketard

TSOW wrote: »

When you say isolated from the ground, you mean that he is floating/electricity is blocked from reaching the ground (Rubber shoes or whatnot)?

Yes, correct.

TSOW

biketard wrote: »

Yes, you could also keep the wire intact and increase the voltage until the guy's share of the current still amounted to 15mA. It would require a bit more working out and would be a serious waste of electricity, but assuming the cable had SOME resistance, and could handle currents large enough to still give the guy his 40mA, it would work.

Is he not supposed to notice or something?

Are you allowed to swap out the wire for one with more resistance?

The wire is left 'unguarded' so I could do that.

TSOW

It's supposed to look 'accidental' lol.

TSOW

I'm gonna go asleep now, thanks for all the help. I'll have another look in the morning with what you've said in mind.

TSOW

If you can think of anything else that might help please post it.
Thanks again!

I'll post the solution tomorrow or at least the gist of it if you're interested...I know I am lol.

biketard

TSOW wrote: »

The wire is left 'unguarded' so I could do that.

OK, well it's all about directing more of the current towards the guy. Since his resistance appears to be fixed, you either do that by increasing the voltage or increasing the other (parallel) resistance. Best way to do that is to cut the cable, but the next best thing would be to increase its resistance in some other way, such as replacing the cable (or reducing the diameter of the one you have now should increase its resistance: http://chemandy.com/calculators/round-wire-resistance-calculator.htm )

What year/grade is this for anyway?

biketard

TSOW wrote: »

I'm gonna go asleep now, thanks for all the help. I'll have another look in the morning with what you've said in mind.

TSOW wrote: »

If you can think of anything else that might help please post it.
Thanks again!

I'll post the solution tomorrow or at least the gist of it if you're interested...I know I am lol.

OK, cool.

TSOW

biketard wrote: »

OK, well it's all about directing more of the current towards the guy. Since his resistance appears to be fixed, you either do that by increasing the voltage or increasing the other (parallel) resistance. Best way to do that is to cut the cable, but the next best thing would be to increase its resistance in some other way, such as replacing the cable (or reducing the diameter of the one you have now should increase its resistance: )

What year/grade is this for anyway?

2nd Year in college...Physics yay...-.-

biketard

So how did you get on, OP?