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>.
Nuclear fusion in the core tries to blow the star apart. Gravity holds it together. Whoever designed that system really knew what he was doing. I'm kinda grateful to him.
Yes that looks correct to me. good luck!!
The lens equation gives d relation between focal length, object distance n image distance.
1/f = 1/v + 1/u
seldon
ANSWER:
The easiest way to get a fairly accurate measure of your water flow rate is to time yourself filling up a bucket. So for example if you fill up a 10 litre bucket in 1.5 minutes, then your flow rate will be: 10/1.5 = 6.66 Litres per minute.