Animals and Current Electricity

[Soaring Crane]

I was glancing at a physics book, and two questions in the electricity section caught my eye.

Why does a cow that touches an electric fence experience a mild shock?

Why can birds perch on high-voltage lines without being injured?

For the second one, I believe it is that their "feet" are better insulated. (Don't some die, however?) What about the first one?

Thanks.

 

[Blistering Peanut]

The one about the bird...

It can perch on one wire without being electrocuted as there is no reason why the electricity should flow through the bird. If the bird was touching the ground as well as the wire current would flow through the bird to be earthed in the ground. Standing on a single wire does not let this happen.

The same reason goes for the cow, current flows through his skin and down through his leg into the Earth and this stimulates the pain receptors and the muscles which give it a shock.

Interestingly I was reading that AC current supplied to our houses has a frequency of 50Hz for the opposite reason to the cow one. Apparently our muscles respond (would resonate be the right word here?) worst to this frequency so we experience a lot less pain and we should be able to release a grip from whatever was giving us the shock.

Please correct me if I'm wrong I haven't quite got onto university physics yet.