Question 7

A very small graphite-coated sphere P is rubbed with a cloth. It is found that the sphere acquires a charge of + 0,5 μC.

7.1 Calculate the number of electrons removed from sphere P during the charging process. (3)

Now the charged sphere P is suspended from a light, inextensible string. Another sphere, R, with a charge of – 0,9 μC, on an insulated stand, is brought close to sphere P. As a result sphere P moves to a position where it is 20 cm from sphere R, as shown below. The system is in equilibrium and the angle between the string and the vertical is 7^o.

7.2 Draw a labelled free-body diagram showing ALL the forces acting on sphere P. (3)

7.3 State Coulomb’s law in words. (2)

7.4 Calculate the magnitude of the tension in the string. (5)

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