A small isolated sphere A, with a mass of 0,2 g, carrying a charge of +7 x 10-9 C,
is suspended from a horizontal surface by a string of negligible mass. A second
sphere B, carrying a charge of -8 x 10-9 C, on an isolated stand, attracts sphere A so
that the string forms an angle of 20ยบ to the vertical. The horizontal distance between
the centres of the two spheres is 3 cm. Refer to the diagram below.
9.1 State Coulomb’s law in words. (2)
9.2 Draw a VECTOR DIAGRAM of the forces acting on sphere A. Indicate at least
ONE angle. (4)
9.3 Calculate the magnitude of the electrostatic force that sphere B exerts on
sphere A. (4)
9.4 Calculate the magnitude of the tension force in the string. (3)
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