Are we free to call the potential of our reference point as + 100 V instead of zero?

A point charge Q is placed at point O as shown in the figure. is the potential difference V_A - V_B positive, negative or zero if Q is postive or negative?

Why do we often regard the potential of the earth to be zero?

What should be the capacitance of a capacitor capable of storing 1J of energy when potential difference of 100V is applied between the plates?

What should be the capacitance of a capacitor capable of storing 1j of energy when potential difference of 100V is applied between the plates?

A electron is accelerated through a potential difference of 100V. What is de-Broglie wavelength associated with it? To which part of the electromagnetic spectrum does this value of wavelength correspond?

A solid metal sphere of radius r has charge +Q. This charge is one the surface of the sphere but it may be considered to be a point charge at its centre. The sphere has radius 36 cm. Determine, for this sphere the capaciance the charge requried to raise the potential of the sphere form zero to 7.0 xx 10^5V .

In the circit show in the figure E_1 = 3V, E_2 = 2V, E_3 = 1V and the resistances R = r_1 = r_2 = r_3 = 1Omega . Find the potential difference between the points A and B and the current through each branch.