A level physics helpWatch

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#1
This is just a 1 mark question so it's probably me being an idiot, but I don't understand this at all

So there's a transmission cable, of +200kV surrounded by equipotentials at 195,190 and 185kV.

The 195kV equipotentials is 5mm away from the surface of the 200kV transmission cable. Use this information to choose the best estimate of the electric field strength on the surface of the cable.
The options are: 40V/m, 1x10^-3 V/m, 1x10^6V/m, 4x10^7V/m.

Now my answer was the last option, because I assumed that the field would be uniform over that 5mm, and so I did 200kV divided by 5mm..... Why is this wrong? The answer is apparently 1x10^6.

Thanks!
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#2
Anyone?
0
5 years ago
#3

which would be 200kv - 195kv = 5kv

therefore using the formula E=v/d

5x10^3 divided by 5x10^-3 (which is the seperation)

=1x10^6
0
5 years ago
#4

which would be 200kv - 195kv = 5kv

therefore using the formula E=v/d

5x10^3 divided by 5x10^-3 (which is the seperation)

=1x10^6

Think of it like energy levels when an electron moves from one orbit to another to find the frequency of the photon emitted you have to find the energy difference in eV
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5 years ago
#5
(Original post by topgun41)
Now my answer was the last option, because I assumed that the field would be uniform over that 5mm, and so I did 200kV divided by 5mm..... Why is this wrong? The answer is apparently 1x10^6.

Thanks!
The field strength has dropped (200kV - 195kV) = 5kV over 5mm.

i.e. the field strength is reducing at the rate of:

5x103V / 0.005m

= 1x106 Vm-1
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