Igcse Model Questions Vol1 2025 Physics Question 40

Three point charges are placed at the vertices of a right‑angled triangle \(ABC\) with the right angle at \(B\). The sides have lengths \(AB = 0.30\ \text{m}\), \(BC = 0.40\ \text{m}\) and \(AC = 0.50\ \text{m}\). The charges are \(q_A = +2.0\ \mu\text{C}\), \(q_B = -3.0\ \mu\text{C}\) and \(q_C = +4.0\ \mu\text{C}\). (a) Determine the magnitude and direction of the net electric field at point \(B\) due to the other two charges. (b) A test charge of \(+1.0\ \mu\text{C}\) is moved from \(B\) to a point \(D\) that is \(0.10\ \text{m}\) directly above \(B\). Assuming the electric field is uniform along this short path and equal to the field at \(B\), calculate the work done on the test charge. (c) Taking the electric potential at \(B\) as zero, find the electric potential at \(D\) due to all three charges. (d) Explain whether the work found in part (b) equals the change in electric potential energy between \(B\) and \(D\), and discuss any discrepancy.