PLEASE HELP THIS IS URGENT!!!!! 50 POINTS!!!
2 answers:
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I attached the full question.
We know that for a parallel-plate capacitor the surface charge density is given by the following formula:
Where V is the voltage between the plates and d is separation.
Voltage is by definition:
Voltage is analog to the mechanical work done by the force.
Above formula is correct only If the field is constant, and we can assume that it is since no function has been given.
The charge density would then be:
Please note that elecric permittivity of air is very close to elecric permittivity of vacum, it is common to use them <span>interchangeably</span>.
We know that for a parallel-plate capacitor the surface charge density is given by the following formula:
Where V is the voltage between the plates and d is separation.
Voltage is by definition:
Voltage is analog to the mechanical work done by the force.
Above formula is correct only If the field is constant, and we can assume that it is since no function has been given.
The charge density would then be:
Please note that elecric permittivity of air is very close to elecric permittivity of vacum, it is common to use them <span>interchangeably</span>.
12 V is the f.e.m. 
of the battery. The potential difference that is applied to the motor is actually the fem minus the voltage drop on the internal resistance r:
this is equal to the voltage drop on the resistance of the motor R:
so we can write:
and using
and 
we can find the current I:
this is equal to the voltage drop on the resistance of the motor R:
so we can write:
and using