7. A 2 C charge and a 8 C charge repel each other with 10 N of force. How much w

Question

7. A 2 C charge and a 8 C charge repel each other with 10 N of force. How much will a 4 C charge and a 4 C charge repel each other when placed the same distance apart?

A) 20 N B) 10 N** C) 8 N D) 40 N

9. Consider two identical insulated metal spheres, A and B. Sphere A initially has a charge of -6.0 units and sphere B initially has an initial charge of -2.0 units. The sphere are brought in contact with each other for a short time and then separated again. What is the charge on each sphere afterward?

A) Sphere A: -6.0 units; sphere B: -2.0 units B) Sphere A: -2.0 units; sphere B: -6.0 units C) Sphere A: -8.0 units; sphere B: -8.0 units D) Sphere A: -4.0 units; sphere B: -4.0 units **

10. If an object has a net negative charge of 4.0 coulombs, the object possesses A) 6.3 1018 more electrons than protons B) 2.5 1019 more electrons than protons** C) 6.3 1018 more protons than electrons D) 2.5 1019 more protons than electrons

11. A positively charged glass rod attracts object X. The net charge of object X

A) may be zero or negative** B) may be zero or positive C) must be negative D) must be positive

12. Electrons are accelerated to reach a kinetic energy of 250 eV (= 4.0 x 10-17 J). If the acceleration is done in a distance of 0.20 m, what is the magnitude of the electric field causing the acceleration?

A) 250 N/C B) 50 N/C C) 2500 N/C D) 1250 N/C

13. Consider a parallel-plate capacitor with area A and plate separation d. What will happen to the capacitance if the area is halved and the distance is doubled?

A) The capacitance will be four times the original capacitance. B) The capacitance will be twice the original capacitance. C) The capacitance will be half of the original capacitance. D) The capacitance will be a quarter of the original capacitance.**

14. Three capacitors with capacitances of 24 F, 36 F, and 48 F, respectively, are connected in series. This combination is then connected to a 12 V battery. What is the charge on the 36 F capacitor?

A) 1.3 mC B) 9.0 C C) 0.13 mC D) 11 C E) 0.43 mC**

15. A 240 F capacitor is connected to a 15 V power supply. What is the energy stored in the capacitor?

A) 1.8 J B) 27 mJ C) 27 J D) 1.8 mJ**

Explanation / Answer

(7) Option (B) 10N is correct.

Explanation: F is proportional to Q1*Q2/r^2

Put the values in both the conditions and get the result.

(9) Option (D) is the correct answer.

Explanation: When two conductors are brought in physical contact with each other, their charges redistribute themselves so that their potentials become equal.

(10) Option (B) is the correct answer.

Explanation: Q = 4 C, q = 1.602*10^-19 C
Net electrons = Q/q
With rounding down:
= 2E+19

(11) Option (A) is the correct answer.

(12) Option (A) is the correct answer.

Explanation: Kinetic energy attained by the electron = 4x10^-17 J

Equalize this with the loss in Potential energy.

(13) Option (D) is the correct answer.

Explanation: The capacitance of a PP capacitor with plate area "A" and plate separation "d" is given by the formula;

C = e(o)A/d

So if "A" is halved and "d" is doubled you get;

C' = e(o)(1/2)A/2d = e(o)A/4d = (1/4)e(o)A/d = (1/4)C

So the new capacitance will be 1/4 the original capacitance.

(14) Option (E) is the correct answer.

(15) Energy stored in a capacitor = (1/2)C*V^2

Now in your question, unit of capacitance is not clear, whether this is micro or nano. Whatever, put the value of volt and capacitance in the above expression and get the result.

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