16-115sp13-elect3.pdf
16-115sp13-elect3.pdf
16-115sp13-elect3.pdf
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Shielding effect in a conducting shell<br />
We know that, due to mobility of electrons in conducting materials<br />
1. E inside a conductor must be zero<br />
2. All excess charge resides on surface<br />
3. External field lines stop (and start again) at right angles<br />
4. A cavity inside the conductor will be shielded against external fields<br />
• External field may cause separation of charge on surfaces, but<br />
net Q = 0, so E inside cavity is 0 also<br />
• Internal charge is not the same!<br />
– Induced Q extends E field outside: Shielding only works one-way<br />
4/29/13 10
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