Electric Charge and Atomic Structure

Electric Charge

• Electric Charge (Q or q) is a measure of whether a body has more or less electrons than protons.
• The unit of electric charge is the coulomb (C).

Atomic Structure

• An atom is composed of three main particles: protons, neutrons, and electrons.
• Protons and neutrons are located in the nucleus (centre of the atom), while electrons orbit around it.

Forces between Charges

• Like charges (i.e., two positive charges or two negative charges) repel each other.
• Unlike charges (i.e., one positive charge and one negative charge) attract each other.

Charging by Friction

• Rubbing cloth against Polythene causes the Polythene to become negatively charged.
• Rubbing cloth against Perplex causes the Perplex to become positively charged.
• This method can be used to demonstrate the forces between charges.

Electric Charge

• Electric Charge (Q or q) is a measure of whether a body has more or less electrons than protons.
• The unit of electric charge is the coulomb (C).

Atomic Structure

• An atom is composed of three main particles: protons, neutrons, and electrons.
• Protons and neutrons are located in the nucleus (centre of the atom), while electrons orbit around it.

Forces between Charges

• Like charges (i.e., two positive charges or two negative charges) repel each other.
• Unlike charges (i.e., one positive charge and one negative charge) attract each other.

Charging by Friction

• Rubbing cloth against Polythene causes the Polythene to become negatively charged.
• Rubbing cloth against Perplex causes the Perplex to become positively charged.
• This method can be used to demonstrate the forces between charges.

Electric Charge and Conductors

• A conductor is a substance that allows electric charge to flow through it.
• An insulator is a substance that prevents electric charge from flowing through it.

Static Charge on Conductors

• Static charges are always found on the outer surface of a conductor.
• On a conductor, static charge tends to accumulate at the pointed regions.
• This is because the charge density is higher at pointed areas, resulting in a stronger electric field.

Point Discharge

• Point discharge occurs at very sharp points due to high charge density.
• At these points, a strong electric field is created, attracting and repelling ions.
• This ultimately neutralizes the object, as demonstrated by the 'electric wind' effect on a naked flame.

Gold Leaf Electroscope

• Used to detect small charges, estimate the size of a charge, identify the sign of the charge, and distinguish between a conductor and insulator.
• Consists of multiple components, including a thin gold leaf placed close to a metal rod.
• When the gold leaf and metal rod have the same sign of charge, they repel each other.

Coulomb's Law

• The force between two point charges is proportional to the product of their charges and inversely proportional to the square of the distance between them.
• The formula for Coulomb's Law is F = Q1Q2/4πEd^2, where F is the force in newtons (N).
• This formula is an example of an inverse square law.
• The size of the force is the same on each body, and the force is along the line between them.

Electrostatic Force

• One of the factors affecting the size of the electrostatic force is the permittivity (ε) of the medium surrounding the charges.
• The permittivity and force are inversely proportional.
• The force is greatest when the charges are in a vacuum, where the permittivity is low.

Electric Fields

• An electric field is a region of space where a static electric charge experiences a force other than gravity.

Key Characteristics

• An electric field line is the path a positive charge would follow if placed in the electric field.

Electric Field Strength

• Electric field strength (𝑬) is the force per unit positive charge at a point in the electric field.
• Measured in newton per coulomb (N C-1) or volt per meter (V m-1).

Note: 𝑬 is the symbol for electric field strength.