Why is the voltage at both ends of each branch equal to the supply voltage in parallel circuit?

Why is the voltage at both ends of each branch equal to the supply voltage in parallel circuit?

In fact, this is only an ideal situation. If we assume that the internal resistance of the power supply is zero, the branch voltage will be equal to the power supply voltage. In fact, the power supply will have internal resistance, so it has to divide the voltage with the external circuit. However, the internal resistance is very small, so the voltage division is relatively small, which can be ignored, Therefore, when it is not strict, we say that the branch voltage is equal to the power supply voltage. As for why the voltage of each branch is equal, for the sake of simplicity and clarity, you can assume that each branch is a pure resistance circuit, and because each branch is in parallel, the resistance of each branch is in parallel to form an equivalent resistance, so the external circuit is equivalent to a resistance, So the voltage it gets is of course the power supply voltage (ignoring the internal resistance of the power supply)

Is the total voltage of the series circuit equal to the supply voltage?

This is true in junior high school
But it's not true in high school
Because the power supply has internal resistance, it should be equal to the road voltage