Point charges +Q and −2Q are fixed on the x-axis at x = 0 and x = 10 cm respectively. A small positive test charge q is placed at x = 4 cm and released.
a. (i) Without calculating any magnitudes, state the direction (towards +x or −x) of the force on q due to each fixed charge separately. Justify your answers.
b. (ii) Hence decide the direction of the net force on q.
c. (iii) If the charge −2Q at x = 10 cm were changed to +2Q, explain qualitatively how the direction and relative magnitude of the net force on q would be affected, giving reasons.