If Lamp2 is disconnected, What will happen to the brightness of the Lamp3?
I think that the brightness will remain the same because Lamp2 is in parallel with the branch that contains Lamp3.
Let's assume that I3 passes in Lamp3. When Lamp2 is disconnected, The total current will be reduced to be equal to I3. So Lamp3 and Lamp4 will not be affected. That's why loads are connected in parallel at home.
This question is in my younger brother's scholar book. The answer was: "The brightness of Lamp3 will increase because the total current will pass through it."
I think I'm missing something but I don't know what it is.