# Electrostatic shielding

1. Jun 1, 2015

### Bhumanyu Arun

My question was was that though you don't have any charge on the inner surface of a metallic cavity but still there's a potential. Can't that potential electrocute someone?

2. Jun 1, 2015

### Geo louv

How you understand that there is no charge????...its metal....and a metal can be charged very easy

3. Jun 1, 2015

### Jeff Rosenbury

The OP is a little vague. But I'll assume this is about a conductive, hollow sphere.

Voltage is relative. So inside a conductive sphere (and lacking any other charges) the voltage is zero at all points referenced to the sphere. If the sphere has a high voltage (i.e. lots of charge) referenced to an outside point, it could indeed shock someone, but only someone who completed the circuit to a conductor outside the sphere. That is hard to arrange (impossible if the sphere is totally closed).

Usually this arises with static electric type equipment. Such equipment rarely has enough current to kill people, at least in demonstration type equipment. (It can give a painful shock though. ) Current kills, not voltage.

4. Jun 3, 2015

### jim hardy

Takes a potential difference to shock you.
A bird can sit on a wire that's at high potential . He could also sit inside a cage at high potential. That cage could be a metallic cavity...

5. Jun 3, 2015

### Jeff Rosenbury

Or "to find that gambling is going on here!" (Casablanca)

6. Jun 4, 2015

### Bhumanyu Arun

Sir what you said was fine. And I perfectly agree with that. But what if we have an arbitrary shaped conductor that's hollow but has a definite thickness. Then all the charges will be accumulated on it's surface. Electric field inside it would be 0 but the potential would be constant. If it's a fact that current shocks and not voltage then thank you a lot for getting my doubt clear.

7. Jun 4, 2015

### Jeff Rosenbury

It takes about 1 mA across the heart to cause cardiac arrest. However the skin has a resistance of several hundred kΩ when dry (much lower when wet) and current through the body often skips the heart. (Other organs can be affected, and sometimes destroyed at higher current levels as well.) So any amount of current is fine at low voltage levels. Your skin protects you. (Unless your skin is broken. Metallic medical needles used to be a common danger.)

Most high voltage demonstration equipment doesn't exceed the 1 mA level, but often experimental equipment does. Use with caution.

8. Jun 5, 2015

### Bhumanyu Arun

Thank you sir. It really helpedn