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Answer: b
Explanation: The standard unit of charge is Coulomb. One coulomb is defined as the 1 Newton of force applied on 1 unit of electric field
Answer: a
Explanation: Coulomb law is applied to static charges. It states that force between any two point charges is proportional to the product of the charges and inversely proportional to square of the distance between them. Thus it is employed in electrostatics.
Find the force between 2C and 1C separated by a distance 1m in air(in newton).
Answer: b
Explanation: F = q1q2/(4∏εor^{2}) = 2 X 9/(10^{9} X 12) = 18 X 10^{9}.
Two charges 1C and 4C exists in air. What is the direction of force?
Answer: c
Explanation: Since the charges are unlike, the force will be attractive. Thus the force directs from 1C to 4C.
Find the force of interaction between 60 stat coulomb and 37.5 stat coulomb spaced 7.5cm apart in transformer oil(εr=2.2) in 10^{4} N,
Answer: d
Explanation: 1 stat coulomb = 1/(3 X 10^{9}) C
F = (1.998 X 1.2488 X 10^{16})/(4∏ X 8.854 X 10^{12} X 2.2 X (7.5 X 10^{2})^{2}) = 1.815 X 10^{4} N.
Find the force between two charges when they are brought in contact and separated by 4cm apart, charges are 2nC and 1nC, in μN.
Answer: c
Explanation: Before the charges are brought into contact, F = 11.234 μN.
After charges are brought into contact and then separated, charge on each sphere is, (q1 + q2)/2 = 0.5nC
On calculating the force with q1 = q2 = 0.5nC, F = 1.404μN.
Answer: b
Explanation: The Coulomb law can be formulated from the Gauss law, using the divergence theorem. Thus it is an implication of Gauss law.
Two small diameter 10gm dielectric balls can slide freely on a vertical channel. Each carry a negative charge of 1μC. Find the separation between the balls if the lower ball is restrained from moving.
Answer: c
Explanation: F = mg = 10 X 10^{3} X 9.81 = 9.81 X 10^{2} N.
On calculating r by substituting charges, we get r = 0.3m.
A charge of 2 X 10^{7} C is acted upon by a force of 0.1N. Determine the distance to the other charge of 4.5 X 10^{7} C, both the charges are in vacuum.
Answer: d
Explanation: F = q1q2/(4∏εor^{2}) , substituting q1, q2 and F, r2 = q1q2/(4∏εoF) =
We get r = 0.09m.
Answer: b
Explanation: The force of two charges with respect with each other is given by F1 and F2. Thus F1 + F2 = 0 and F1 = F2.
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