Question 1
(a) Three charges q1, q2 and q3 lie along the x-axis. Charge q1 = 2.5 µC is at x = 1.5 m, while charge q2 = 6.3 µC is at the origin. Where must the third (negative or positive) charge q3 be placed on the axis so that the resultant force on it is zero?
(b) An electron is released from rest in a uniform electric field and accelerates to the north at a rate of 12.5 m/s². Find
(i) the magnitude of the electric field and
(ii) show the direction of the electric field and acceleration on a well labelled diagram.
(c) An electric dipole consisting of charges of magnitude 1.50 nC separated by 6.20 µm is in an electric field of strength 1100 N/C. What is the magnitude of the electric dipole moment?
(d) A flat sheet of paper of area 0.250 m² is oriented so that the normal to the sheet is at an angle of 60° to a uniform electric field of magnitude 14 N/C.
(i) Find the magnitude of the electric flux through the sheet.
(ii) For what angle between the normal to the sheet and the electric field is the magnitude of the flux through the sheet largest? Explain your answer.
(e) A point charge q1 is held stationary at the origin. A second charge q2 is placed at point a, and the electric potential energy of the pair of charges is Ui = +5.4 x 10⁻⁸ J. When the second charge is moved to point b, the electric force on the charge does -1.9 x 10⁻⁸ J of work.
(i) What is the electrical potential energy Uf of the pair of charges when the second charge is at point b?
(ii) What is the electric potential at b, if charge q2 = 1.45 x 10⁻⁶ C?