# Tag Info

## Hot answers tagged electromagnetism

### Why can't current flow in a conductor with a potential/emf on one end and earth on the other? Is there a mathematical expression?

Let's say I have a wire with one end connected to earth and the other end floating. If one end is earthed, then the other end is not 'floating', but also connected to earth by the wire. Perhaps ...
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Accepted

### Significance of electric field for electromagnetic compatibility standards

EM wave will have both the fields while traveling in free space then why standards mention only electric field strength Because the amplitude of the E-field (the electric field strength in volts per ...
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### Doubling the length of a solenoid doubles its inductance. Two identical solenoids in series have up to four times the inductance due to M. Why?

Regarding the air solenoid described by your first formula: - An air solenoid will not have 100% coupling between successive turns. It might be about 95% for two fairly tightly wound turns The ...
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### Significance of electric field for electromagnetic compatibility standards

They're not -- IEC 61000-4-8 Power Frequency Magnetic Field Immunity Test for example is specified in terms of A/m. (Well, if I ignore the parenthetical specifier, anyway.) Most RF probably specs ...
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### Doubling the length of a solenoid doubles its inductance. Two identical solenoids in series have up to four times the inductance due to M. Why?

"Perfect coupling" doesn't mean quite what you think it means :) See this figure from Radiotron Designer's Handbook 4th ed.: For two solenoids butted end-to-end, S = 0 (top curve) and the ...
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### Significance of electric field for electromagnetic compatibility standards

In the far field, the electric field strength is directly linked to the magnetic field strength via the "free space impedance" of ~377 Ohms. So by specifying the electric field strength the ...
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### Doubling the length of a solenoid doubles its inductance. Two identical solenoids in series have up to four times the inductance due to M. Why?

You're cheating yourself in your simplifications. :-) You correctly write: \begin{align} L_{\text{tot}}&=L_1+L_2+2M \\ &\stackrel{L_1=L_2=L_0}{\Rightarrow} \\ L_{\text{tot}}&=2L_0+2kL_0 \...
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1 vote

### Lawn mower robot boundary wire magnetic field

Most likely the wire is not just creating a simple DC magnetic field, but alternating at some frequency, and the robot has a sensor tuned to the same frequency. Rejecting other frequencies greatly ...
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Accepted

### Why can't current flow in a conductor with a potential/emf on one end and earth on the other? Is there a mathematical expression?

why does current only flow in a closed loop? Is there a mathematical representation/symbolic equation that shows this electrical property? The full answer is "Maxwell's equations", but that ...
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