Question 7

7.1 A small sphere, Y, carrying an unknown charge, is suspended at the end of a   light in extensible string which is attached to a fixed point. Another sphere, X, carrying a charge of +6 x10-6 C, on an insulated stand is brought close to sphere Y.

Sphere Y experiences an electrostatic force and comes to rest 0,2 m away from sphere X, with the string at an angle of 10° with the vertical, as shown in the diagram below.

7.1.1 What is the nature of the charge on sphere Y? Choose from POSITIVE or NEGATIVE. (1)

7.1.2 Calculate the magnitude of the charge on sphere Y if the magnitude of the electrostatic force

acting on it is 3,05 N.       (3)

7.1.3 Draw a labelled free-body diagram for sphere Y.           (3)

7.1.4 Calculate the magnitude of the tension in the string.      (3)

7.2 2 Two small charged spheres, A and B, on insulated stands, with charges  +2 x10-5 C and -4 x10-5 C
respectively, are placed 0,4 m apart, as shown in the diagram below. M is the midpoint between
spheres A and B.

7.2.1 Define the term electric field at a point.     (2)

7.2.1 Calculate the net electric field at point M.            (6)

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