Answer:
n = 756.25 giga electrons
Explanation:
It is given that,
If the charge on the negative plate of the capacitor, 
Let n is the number of excess electrons are on that plate. Using the quantization of charges, the total charge on the negative plate is given by :

e is the charge on electron

or
n = 756.25 giga electrons
So, there are 756.25 giga electrons are on the plate. Hence, this is the required solution.
The height difference is found by

Then the change in potential energy is
Answer:
Assuming there is no heat loss to the surrounding.
Heat lost by iron equals heat gained by water.
0.2(450)(50-x)=0.2(4200)(x-30)
x=31.94 °C
Explanation:
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If we will connect the resistors 2ohms, 3ohms, 5ohms in series and the 10ohms resistance parallel then we get equivalent resistance of 5 ohms.
The equivalent circuit is,
R equivalent for the series connection is,

The equivalent resistance is 5 ohms.
So your friend is saying true.