Electrostatics | Jamb(UTME)

Existence of Positive and Negative Charges in Matter

1. Matter is made up of atoms, which contain protons, neutrons, and electrons.
2. Protons have a positive charge, while electrons have a negative charge.
3. Neutrons are neutral and do not carry any charge.
4. The charges of protons and electrons are equal in magnitude but opposite in nature.
5. In an atom, the number of protons equals the number of electrons, making the atom electrically neutral.
6. If an atom loses or gains electrons, it becomes charged, forming an ion.
7. A positively charged ion forms when an atom loses electrons.
8. A negatively charged ion forms when an atom gains electrons.
9. Opposite charges (positive and negative) attract each other.
10. Like charges (positive-positive or negative-negative) repel each other.
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Charging a Body by Friction

11. When two objects are rubbed together, electrons can transfer from one object to the other.
12. The object that gains electrons becomes negatively charged.
13. The object that loses electrons becomes positively charged.
14. Materials like rubber and wool can easily exchange electrons during friction.
15. This process is called charging by friction.
16. For example, rubbing a plastic comb against dry hair charges the comb.
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Charging a Body by Contact

17. A charged object can transfer its charge to a neutral object by direct contact.
18. In this process, electrons move from the charged object to the neutral object.
19. The neutral object takes on the same type of charge as the charged object.
20. For instance, touching a charged metal rod to a neutral metal sphere transfers the charge.
21. The total charge is conserved during the process.
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Charging a Body by Induction

22. Charging by induction occurs without direct contact between objects.
23. A charged object is brought near a neutral object, causing a redistribution of charges in the neutral object.
24. The side closer to the charged object gains an opposite charge, while the farther side gains a like charge.
25. If the neutral object is grounded, charges of one type can escape, leaving it charged.
26. For example, bringing a negatively charged rod near a metal sphere induces a positive charge on the sphere.
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Electroscope

27. An electroscope is a device used to detect the presence of charge on an object.
28. It consists of a metal rod connected to thin metal leaves inside a glass container.
29. When a charged object touches or is brought near the rod, the leaves repel or attract each other, indicating a charge.
30. The degree of movement of the leaves depends on the magnitude of the charge.
31. Electroscopes can be used to determine the type of charge using induction.
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Coulomb’s Inverse Square Law

32. Coulomb's law explains the force between two charged objects.
33. The force between charges is directly proportional to the product of their magnitudes.
34. It is inversely proportional to the square of the distance between them.
35. The formula is $F = k \cdot \frac{q_1 q_2}{r^2}$, where $F$ is the force, $q_1$ and $q_2$ are charges, $r$ is the distance, and $k$ is Coulomb's constant.
36. The force is attractive for opposite charges and repulsive for like charges.
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Electric Field and Potential

37. An electric field is a region around a charged object where another charged object experiences a force.
38. The direction of the electric field is away from positive charges and toward negative charges.
39. Electric potential is the work done in bringing a unit positive charge from infinity to a point in the field.
40. Electric potential is measured in volts (V).
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Electric Field Intensity, Potential, and Potential Difference

41. Electric field intensity is the force experienced by a unit positive charge in the electric field.
42. It is measured in newtons per coulomb (N/C).
43. Potential difference is the difference in electric potential between two points in an electric field.
44. It is also measured in volts (V).
45. A higher potential difference causes a stronger electric field.
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Electric Discharge and Lightning

46. Electric discharge is the sudden release of static electricity from one object to another.
47. It occurs when the potential difference between objects is high enough to overcome resistance.
48. Lightning is a natural example of electric discharge.
49. It happens when charged clouds discharge to the ground or to other clouds.
50. Lightning is accompanied by light, heat, and sound energy.
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Additional Key Points

51. Static electricity refers to charges that remain at rest on an object’s surface.
52. Conductors allow charges to flow freely, while insulators do not.
53. Grounding allows excess charges to safely flow into the earth.
54. The electric field lines around a positive charge point outward.
55. The electric field lines around a negative charge point inward.
56. Electric field strength decreases with distance from the charge.
57. Potential energy in an electric field depends on the charge and its position.
58. Lightning rods are used to safely direct lightning to the ground.
59. A spark is a visible electric discharge caused by ionization of air.
60. Static electricity has practical uses, such as in photocopiers and air purifiers.

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