Calculation of Electric Potential at the Centre of the Square
Electric potential at a point due to a charge is given by the formula:
\[V = \frac{kQ}{r}\]
where \(V\) is the electric potential, \(k\) is the electrostatic constant, \(Q\) is the charge, and \(r\) is the distance between the charge and the point.

Given Charges and Side Length of the Square
- \(Q_1 = 100 \mu C\)
- \(Q_2 = -50 \mu C\)
- \(Q_3 = 20 \mu C\)
- \(Q_4 = -60 \mu C\)
- Side length of the square = \(\sqrt{2} m\)

Calculating the Electric Potential at the Centre
1. First, calculate the distance from the center of the square to each charge (which is the half of the side length, i.e., \(\frac{\sqrt{2}}{2} m\)).
2. Next, calculate the electric potential due to each charge at the center using the given formula.
3. Now, take the sum of the electric potentials due to all the charges to get the total electric potential at the center.

Summarizing the Calculation
- Distance from the center to each charge: \(\frac{\sqrt{2}}{2} m\)
- Electric potential due to \(Q_1\): \(V_1 = \frac{kQ_1}{\frac{\sqrt{2}}{2}}\)
- Electric potential due to \(Q_2\): \(V_2 = \frac{kQ_2}{\frac{\sqrt{2}}{2}}\)
- Electric potential due to \(Q_3\): \(V_3 = \frac{kQ_3}{\frac{\sqrt{2}}{2}}\)
- Electric potential due to \(Q_4\): \(V_4 = \frac{kQ_4}{\frac{\sqrt{2}}{2}}\)
- Total electric potential at the center: \(V_{total} = V_1 + V_2 + V_3 + V_4\)
By calculating the above values using the given charges and side length, you can determine the electric potential at the center of the square.