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electric field between capacitors

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puffylover

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aamc 4 problem 41 on the ps section

which of the following changes to the circuit will decrease the electric field between the electrodes by the greatest amount.

the circuit consists of a resistor and capacitor (resistor is a at a higher potential/before the capacitor)

answer: increasing d (distance between plates) by a factor of 2

explanation: for a fixed voltage between the cathode and anode, the electric field is inversely proportional to the distance between them. increasing the circuit resistance for a fixed current will decrease the electric field, but not by as much as does the length change

E= (V-IR)/L

so my question is: how come the current is considered constant. doesn't the current go down if the resistance of the circuit goes up?
 

lorenzomicron

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aamc 4 problem 41 on the ps section

which of the following changes to the circuit will decrease the electric field between the electrodes by the greatest amount.

the circuit consists of a resistor and capacitor (resistor is a at a higher potential/before the capacitor)

answer: increasing d (distance between plates) by a factor of 2

explanation: for a fixed voltage between the cathode and anode, the electric field is inversely proportional to the distance between them. increasing the circuit resistance for a fixed current will decrease the electric field, but not by as much as does the length change

E= (V-IR)/L

so my question is: how come the current is considered constant. doesn't the current go down if the resistance of the circuit goes up?


yes, the current will go down as the resistance goes up if the voltage is fixed. However, if the current is fixed, then other things can happen.
however, in the capacitor case, the electrical field is changed most by the distance between the plates because E is supposed to be constant and if the voltage does not increase between the plates, increasing the distance will largely decrease the field to conserve the voltage.

also...i am not clear as to what your circuit looks like....clarify?
 
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