Resistance and Increase in Current

[Peter G.]

I was reading about resistance and it said that resistors are used to limit the current in a circuit. How does a resistor reduce the current in a series circuit? They lose energy therefore they move slower? Or does it simply prevent electron flow?

In addition to that, how does adding more batteries in a series circuit increase the current? Well, I mean: In the example there is a series circuit with an ammeter, and a resistor with a voltmeter connected to measure the potential difference across the resistor or across the battery I can't remember, but there was just one resistor anyway. The resistor was the same: Whenever batteries were added, the potential difference increased and the current increased. I am guessing the current was still the "same" but with more energy (voltage) a greater current was able to be pushed through the resistor.

 

[Delphi51]

Yes, the greater the potential the more current that goes through the resistance. The formula is I = V/R (current = voltage divided by resistance). The human body is similar to a resistance. If you touch your hands to a 12 Volt car battery, so little current goes through you that you don't even feel a shock. A 120 Volt source is quite different.

 

[Peter G.]

Ah ok, got it.

I am just having a bit of trouble with a more specific problem. Towards the end of the resistance video they portray a parachutist holding on with both his hands to a power line cable. It says that the parachutist does not experience a shock because the potential difference between both his hands is very small, not allowing current to run through his body. However, the charge, I believe, has quite a lot of energy, due to its high voltage, enabling a big potential difference if it goes through a resistor. So wouldn't that charge running through him, a resistance, allow a lot of current to run through him? I am thinking he does not get electrocuted because the electricity is being transported at very low current to avoid energy lost by heat so, no matter the potential difference, the current from a start is already pretty low.

Do you think you can help me clear this out?

 

[Delphi51]

The guy must be holding onto just one cable. If he had his hands on two cables with a few KV potential difference between them, he would indeed get roasted. But touching one, no current flows because their is no complete circuit.

Holding two hands on one wire with half a meter between them, there would be a tiny potential difference between hands. Power lines typically have a resistance of a few ohms per km, but the resistance between hands and the resulting V = I*R potential difference from one hand to the other would be too small to notice.