Two small spheres of masses M
1, and M
2 are suspended by weightless insulating threads of lengths L
1, and L
2. The spheres carry charges of Q
1, and Q
2 respectively. The spheres are suspended such that they are in level with one another and the threads are inclined to the vertical at angles of 8, and 0, as shown. Which one of the following conditions is essential, if q, = q
2?
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