Physics education research, electronic materials, and the musings of Christopher Moore, Ph.D.

tamara wrote:

Thanks for the response about the birds and power lines, Martin.  I just have a few follow up questions if you wouldn't mind . 

I believe I read somewhere else on the internet that you would also become electricuted if you were hanging on to a power line were you to reach out and touch anything else (even if it weren't another power line), but even like the ground or another object---is this true?

The first requirement is that there be a potential difference between the two objects that you touch. If there is, current will flow through you (you are acting as a resistor connected between two terminals of a voltage source). The amount of current that flows is essentially determined by Ohm's Law. Will it be enough to electrocute you? Well, that depends on two key factors:

1. The total amount of energy delivered to your body. This is simply the potential difference (energy per unit charge) multiplied by the current (charge per unit time) multiplied by the length of time you remain in contact with the two objects.

2. The path that the current takes as it flows through—and delivers energy to—your body. In other words, does the current pass through any vital organs, which are more "fragile" than non-vital organs (e.g., if the path runs through your heart you're more likely to be killed than if it runs only through fat or muscle tissue)?

tamara wrote:

And, as for the household appliance electricutions, I know you would become electricuted if you touched two uninsulated wires at the same time (were there sufficient difference in potential), but since the wires to the electric appliances in our homes are insulated (chords), you wouldn't be able to become electricuted if you just grabbed two chords at the same time, would you?  The insulation is a non-conductor so it blocks the flow to us, right?  And since power lines aren't insulated, that's why they are so dangerous?

Correct. In fact, the three-pronged plugs and outlets that today are commonplace in homes and office buildings were introduced to help reduce the risk of electrocution should an appliance's internal wiring accidentally "short out" due to failed insulation (or otherwise somehow become loose) to the metal casing or handle that appliances often incorporate. The third prong serves as a "zero-resistance" connection ("shunt") from the internal metal casing/handle to the external (to your home/office) ground (zero potential), providing a least-resistance path for the electricity to flow. Without that path, an accidental short could (and often did) result in the current flowing through the unfortunate user as it tried to find its own way to a lower potential.

tamara wrote:

Why aren't power lines insulated?

No one expects that Tamara will be climbing power-line poles anytime soon.

tamara wrote:

One more question: Plastic is a non-conductor, right?  Yet I know that it is highly flammable.  I have pet rabbits and I have to cover the chords in my home with plastic tubing, so they won't chew through the wires.  Besides being a non-conductor and a barrier to chewing, why is plastic a good choice for covering a wire? Electricity can cause fires, right?  And plastic is highly flammable......isn't there some kind of risk here, like if there were already a break in the chord?

Insulation (such as plastic) needs to be "appropriate" to the application. That means that it must be (a) a "poor" conductor of electricity for the voltages and currents that the wires will be carrying; (b) a "good" thermal insulator, to be able to handle any heat that is dissipated by the metal wires as a result of electrical power loss due to the resistance of the wires; and (c) thick enough to withstand environmental stresses (such as gnawing bunny rabbits ).

tamara wrote:

I'm just curious...............thanks:)

Next time, post your follow-up question within the same thread as your original question. I had no idea you had posted this, and never would have known you had posted this, had I not decided to check the forum today. However, when you post a follow-up, the board automatically notifies all subscribers to the thread that a new reply has been posted.

tamara wrote:

Thanks for your responses, Martin.  Don't worry, I don't plan on hanging from power lines. (very funny)

Good. Now, just keep an eye on those bunny rabbits.