19.3b FM19 P42 Q6 Smoothing of Voltage | A2 Capacitance | Cambridge A Level 9702 Physics

[@alijaved7636]

At 11:40 wont 4 be the final voltage and 7 the initial. Why did we use it the other way?

[@ETphysics]

You can also do that method, and get a negative change in energy for the capacitor! But since energy loss in capacitor = energy gain in resistor, we can ignore the negative sign and both ways work.