Answer:
(a) Both the charges are positive or negative.
(b) Teh value of each charge is 1.53 x 10^-5 C.
Explanation:
Spring constant, K = 340 N/m
Natural length, L = 0.4 m
stretch, y = 0.033 m
(a) Let the charge on each sphere is q and they repel each other so the nature of charge of either sphere may be both positive or both negative.
(b) The electrostatic force is balanced by the spring force.

Answer:
It's convection
Explanation:
As the hot place transfers heat to the liquid substance, it becomes less dense and rises to the surface given rise for cooler molecules directly above to fall and so undergoes the same circle. In the process the less dense particles are so light that it's swayed into the atmosphere. In the process drying is ensued.
Complete Question
The complete question is shown on the first uploaded image
Answer:
The strain experienced by the specimen is 0.00116 which is option A
Explanation:
The explanation is shown on the second uploaded image
Not sure the precise concept of "normal observation", but I assume that is observed by "eyes".
Eye observation is basically macroscopic, but when you use a mark, which can be regarded as a point of mass, then it goes to microscopic.
Mark is a reference point which you can compare the relative position change, but with your eyes, first you cannot notice microscopic changes, second the eyes cannot precisely set a stable reference point.