We can charge a metal sphere positively without touching it by:

1. Conduction

2. Induction

3. Friction

4. Both (1) and (2)

Subtopic:  Electric Charge |
 71%
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If 109 electrons move out of a body to another body every second, how much time approximately is required to get a total charge of 1on the other body?
1. 200 years
2. 100 years
3. 150 years
4. 250 years

Subtopic:  Electric Charge |
 58%
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The amount of positive and negative charges in a cup of water (250 g) are respectively:

1. 1.6×109 C, 1.4×109 C
2. 1.4×109 C, 1.6×109 C
3. 1.34×107 C, 1.34×107 C
4. 1.6×108 C, 1.6×107 C
Subtopic:  Electric Charge |
 69%
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The ratio of the magnitude of electric force to the magnitude of gravitational force for an electron and a proton will be:
(mp=1.67×1027 kgme=9.11×1031 kg)
1. 2.4×1039
2. 2.6×1036
3. 1.4×1036
4. 1.6×1039

Subtopic:  Coulomb's Law |
 60%
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A charged metallic sphere A is suspended by a nylon thread. Another identical charged metallic sphere B held by an insulating handle is brought close to A such that the distance between their centres is 10 cm, as shown in Fig.(a). The resulting repulsion of A is noted. Then spheres A and B are touched by identical uncharged spheres C and D respectively, as shown in Fig.(b). C and D are then removed and B is brought closer to A to a distance of 5.0 cm between their centres, as shown in Fig. (c). What is the expected repulsion on A on the basis of Coulomb’s law?

1. Electrostatic force on A due to B remains unaltered.
2. Electrostatic force on A due to B becomes double.
3. Electrostatic force on A due to B becomes half.
4. Can't say.
Subtopic:  Coulomb's Law |
 68%
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Consider three charges q1, q2, q3 each equal to q at the vertices of an equilateral triangle of side l. What is the force on a charge Q (with the same sign as q) placed at the centroid of the triangle, as shown in the figure?

     
1. 34πϵ0Qql2
2. 94πϵ0Qql2
3. zero
4. 64πϵ0Qql2

Subtopic:  Coulomb's Law |
 87%
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Consider the charges q, q, and q placed at the vertices of an equilateral triangle, as shown in the figure. Then the sum of the forces on the three charges is:

    

1. 14πϵ0q2l2
2. zero
3. 24πϵ0q2l2
4. 34πϵ0q2l2

Subtopic:  Coulomb's Law |
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An electron falls through a distance of 1.5 cm in a uniform electric field of magnitude 2×104 N/C [figure (a)]. The direction of the field is reversed keeping its magnitude unchanged and a proton falls through the same distance [figure (b)]. If te and tp are the time of fall for electron and proton respectively, then:

   
1. te=tp
2. te>tp
3. te<tp
4. none of these

Subtopic:  Electric Field |
 61%
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Two-point charges q1 and q2, of magnitude +10-8 C  and -10-8 C, respectively, are placed 0.1 m apart. The electric field at point  A (as shown in the figure) is: 

          

1. 3.6×104 NC-1
2. 7.2×104 NC-1
3. 9×103 NC-1
4. 3.2×104 NC-1

Subtopic:  Electric Field |
 56%
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Two charges ±10 μC are placed 5.0 mm apart. The electric field at a point P on the axis of the dipole 15 cm away from its centre O on the side of the positive charge, as shown in the figure is:

1. 2.7×105 NC1 2. 4.13×106 NC1
3. 3.86×106 NC1 4. 1.33×105 NC1
Subtopic:  Electric Dipole |
 58%
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