Explanation:
When there is no change in chemical composition of a substance then it is known as physical change.
When we say that mass is conserved during a physical change then it means that total mass of the substance or object will remain the same from beginning till the end.
For example, a metal box of mass 20 grams is beaten with hammer. Its shape will change which is a physical change and after beaten with the hammer its mass still remains 20 grams.
Because for that you need to build dams and other mega construction.. which is not possible for every country as they have many economical problems asli they have to be in large number to generate power which can feed the whole globe.. which is again difficult due to over population.
" <em>Energy is never created or destroyed.</em> "
All the rest is commentary.
(a) The capacitance of the capacitor is:
![C=4 \mu F=4 \cdot 10^{-6}F](https://tex.z-dn.net/?f=C%3D4%20%5Cmu%20F%3D4%20%5Ccdot%2010%5E%7B-6%7DF)
and the voltage applied across its plates is
![V=12.0 V](https://tex.z-dn.net/?f=V%3D12.0%20V)
The relationship between the charge Q on each plate of the capacitor, the capacitance and the voltage is:
![C= \frac{Q}{V}](https://tex.z-dn.net/?f=C%3D%20%5Cfrac%7BQ%7D%7BV%7D%20)
and re-arranging it we find the charge stored in the capacitor:
![Q=CV=(4 \cdot 10^{-6} F)(12.0 V)=4.8 \cdot 10^{-5} C](https://tex.z-dn.net/?f=Q%3DCV%3D%284%20%5Ccdot%2010%5E%7B-6%7D%20F%29%2812.0%20V%29%3D4.8%20%5Ccdot%2010%5E%7B-5%7D%20C)
(b) The electrical potential energy stored in a capacitor is given by
![U= \frac{1}{2}CV^2](https://tex.z-dn.net/?f=U%3D%20%5Cfrac%7B1%7D%7B2%7DCV%5E2%20)
where C is the capacitance and V is the voltage. The new voltage is
![V=1.50 V](https://tex.z-dn.net/?f=V%3D1.50%20V)
so the energy stored in the capacitor is