Electric Charge & Electric Field - Lesson 1

Electric Charge & Electric Field - Lesson 1

• Electricity's discovery is a cumulative process, not attributed to one person. It spanned from ancient observations to advancements in electromagnetism.
• Thales of Miletus (620-550 BCE) is credited with the initial discovery of amber attracting fur in ancient Greece.
• This early observation predates any understanding of electrical currents being put to practical use by centuries.
• Benjamin Franklin experimented with lightning and electrical conductors. Though details are not precise, he sought to prove electrical nature of lightning.
• Franklin wasn't alone, a French experimenter named Thomas-François Dalibard also obtained electrical discharges from thunderclouds in 1752.
• A French experimenter, Dalibard, who read Franklin’s writings, successfully obtained an electrical discharge from a thundercloud using a metal pole.
• Electric charge is a fundamental property of subatomic particles, causing them to experience forces in electric and magnetic fields.
• Charged particles experience observable effects as a result of field interaction.

Types of Electric Charge

• Electric charge comes in two types: positive and negative.
• Protons carry positive charge (located in the nucleus of an atom). Represented by⁺.
• Electrons carry negative charge (orbiting the atomic nucleus). Represented by⁻.
• The distinction between charges, positive versus negative, is crucial for understanding their interaction.

Electric Attraction and Repulsion

• Opposite charges attract each other, positive and negative.
• Like charges repel each other, either positive and positive, or negative and negative.

Properties of Electric Charge

• Objects with equal positive and negative charges cancel out resulting in a neutral state.
• Electric charge is quantized. This means electric charges are discrete, only occur in integral multiples of a fundamental unit (e).
• The value of this fundamental unit of charge is 1.6 × 10⁻¹⁹ C which is the charge of a single electron or proton.

Measuring Electric Charge

• The unit of electric charge is the Coulomb (C).

• One coulomb is the quantity of charge transferred in one second.

• Mathematically: Q = It, where Q is the charge, I is the current, and t is the time in seconds.

• Ampere is the unit of electric current, equal to 1 Coulomb/second. named after Andre-Marie Ampere.

• One Ampere (A) represents 6.24×10¹⁸ charge carriers moving in one second.

• The relationship between ampere and coulomb is represented as: Ampere = 1 Coulomb/Second

• The total charge of a system is the algebraic sum of individual charges within it.

• For example, a positive charge of +3 units and a negative charge of -2 units would result in a net charge of +1 unit.

• In an isolated system, electric charge is conserved over time—not created or destroyed.

Coulomb's Law

• The force between two charges is directly proportional to the product of their magnitudes and inversely proportional to the square of their separation distance.
• Symbolically: F = k|q₁q₂|/r², where F is the electrostatic force, k is Coulomb's constant, q₁ and q₂ are the charges, and r is the separation distance between them. k has values of 8.988 × 10⁹ N⋅m²/C².
• The electrostatic force is a vector quantity.
• The force acts along the line joining charges.

Charging Objects

• There are three methods of charging objects:
  • Charging by friction: Rubbing two objects transfers electrons from one to the other.
  • Charging by conduction: Transferring charge through direct contact.
  • Charging by induction: Transferring charge through interaction without direct contact, using redistribution of charges.
• A charged item, interacts with an uncharged body; electrons transfer causing similar charges to accumulate.

Electric Field

• An electric field is a property associated with each point in space where a charge is present.
• This field describes how a force acting on a test charge placed at that point.
• Electric field intensity (E) is the force per unit charge at a given point in an electric field.
  • E = F/q₀, where E is the electric field intensity, F is the electrosatic force, and q₀ is the test charge.
• The unit of electric field intensity is Newton/Coulomb (N/C).
• The electric field lines always start from positive charges and end on negative charges. There are four key properties of electric field lines:
  • tangent to the direction of the field
  • greater the line density, greater the magnitude of the field
  • lines start at positive charges and end on negative charges
  • lines never cross
• The magnitude of an electric field is calculated as E = k|Q|/r², where k is Coulomb's constant, Q is the charge, and r is the distance from the charge.

Explore the historical development of electricity and electric charge in this quiz. From Thales of Miletus to Benjamin Franklin and beyond, learn how ancient observations laid the groundwork for our understanding of electromagnetism. Test your knowledge on key figures and events that shaped the field of electricity.