1. Q20. Electric Charge Force and Field

2. A small object has charge Q
A small object has charge Q. Charge q is removed from it and placed on a second small object. The two objects are placed 1 m apart. For the force that each object exerts on the other to be a maximum, q should be :
2 Q Q
Q / 2
Q / 4
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3. Q  q q 
( max )

4. Two identical conducting spheres A and B carry equal charge
Two identical conducting spheres A and B carry equal charge. They are separated by a distance much larger than their diameters. A third identical conducting sphere C is uncharged. Sphere C is first touched to A, then to B, and finally removed. As a result, the electrostatic force between A and B, which was originally F, becomes :
F / 2
F / 4
3F / 8
F / 16
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5. Spheres identical  Charges are shared equally after contact
A, Q
B, Q
C, 0
Spheres identical  Charges are shared equally after contact
After C touching A :
After C touching B :
Final force between A & B :

6. Particles 1, with charge q1, and 2, with a charge q2, are on the x axis, with particle 1 at x = a and particle 2 at x  –2a. For the net force on a third charged particle at the origin to be zero, q1 and q2 must be related by q2  :
2 q1
4 q1
– 2 q1
– 4 q1
– q1 / 4
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7. 2a q a q2 q1 

8. A particle with charge 2 C is placed at the origin
A particle with charge 2 C is placed at the origin. An identical particle, with the same charge, is placed 2 m from the origin on the x axis, and a third identical particle, with the same charge, is placed 2 m from the origin on the y axis. The magnitude of the force on the particle at the origin is
9.0  10–3 N
6.4  10–3 N
1.3  10–2 N
1.8  10–2 N
3.6  10–2 N
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9. y = 2 m
q = 2C
x = 0
q = 2C
x = 2 m
q = 2C

10. just use R for the distance just use 2R for the distance
A charge Q is spread uniformly along the circumference of a circle of radius R. A point particle with charge q is placed at the center of this circle. The total force exerted on the particle q can be calculated by Coulomb's law :
just use R for the distance
just use 2R for the distance
just use 2p R for the distance
result of the calculation is zero
none of the above
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11. Q q R
f  0 by symmetry.

12. A particle with charge Q is on the y axis a distance a from the origin and a particle with charge q is on the x axis a distance d from the origin. The value of d for which the x component of the force on the second particle is the greatest is : a
a  2
a / 2
a /  2
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13. Q r a f d q 

14. A particle with a charge of 5  10–6 C and a mass of 20 g moves uniformly with a speed of 7 m/s in a circular orbit around a stationary particle with a charge of 5  10–6 C. The radius of the orbit is :
0.23 m
0.62 m
1.6 m
Orbit is impossible
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15. Circular motion requires a centripetal force.
Q = 5  10–6 C
m = 20 g
v = 7 m/s
q = 5  10–6 C R
Circular motion requires a centripetal force.
Coulomb force between the particles is however repulsive, and hence centrifugal.