Physics Chapter: Acceleration and Electric Fields

Chapter One: Electric Charges and Fields

• Introduction: Students experience electric sparks and crackling sounds when taking off synthetic clothes in dry weather; lightning is another common example. These are caused by the discharge of static electricity, which arises from the accumulation of charges due to rubbing insulating surfaces. Electrostatics studies stationary charges.

1.1 Introduction

• All students experience static electricity, like sparks or crackling, on taking off synthetic clothes.
• Lightning during thunderstorms is another common example.
• These experiences are due to the discharge of electric charges accumulated through rubbing insulating surfaces.
• Static electricity refers to phenomena where charges do not move with time.
• Electrostatics is the study of stationary electrical charges.

1.2 Electric Charge

• Thales of Miletus (600 BC) discovered static electricity (amber rubbed with wool).
• Substances acquire an electric charge when rubbed together. 
• Like charges repel, unlike charges attract.
• Electric charges can be positive or negative.
• Neutral objects have balanced charges, and are not electrified.

1.3 Conductors and Insulators

• Conductors allow charges to move freely; Examples include metals, human bodies.
• Insulators hinder charge movement: Examples include glass, plastic, wood.
• Charges on conductors spread out over the entire surface.
• Charges on insulators remain localized.

1.4 Basic Properties of Electric Charge

• Additivity: Electric charges add algebraically.
• Quantization: All free charges are integral multiples of the elementary charge (e).
• Conservation: In an isolated system, the total charge is constant; charges aren’t created or destroyed, just transferred.

1.4.3 Quantisation of charge

• Experimentally, it has been established that the charge (q) on any body is always an integral multiple of a fundamental unit of charge (e). This fundamental unit of charge is the charge carried by a proton or an electron given by the following equation

• q=ne

• where n is any integer, which can be positive or negative.

• The charge of an electron is -1.602192 × 10-19 C.

• and that on a proton, is + 1.602192 × 10⁻¹⁹ C.

1.5 Coulomb's Law

• Coulomb's law gives the magnitude of the force between two point charges.
• Force is proportional to the product of the magnitude of the two charges and inversely proportional to the square of the distance between them.
• Force acts along the line joining the charges.
• Coulomb's Law is represented by
• F =k(q1q2)/r^2, where k is coulomb's constant

1.7 Electric Field

• A charge creates an electric field that exerts a force on any other charge placed nearby.
• The electric field vector (E) at a point in space is defined as the force per unit positive charge at that point.

1.8 Electric Field Lines

• Electric field lines are continuous curves that indicate the direction and strength of an electric field.
• Field lines originate from positive charges to negative charges, or extend to infinity.
• The density of field lines is proportional to the strength of the electric field.

1.9 Electric Flux

• Electric flux is a measure of how much electric field passes through a given surface
• Flux is the product of the component of the electric field perpendicular to the surface and the area.

1.10 Electric Dipole

• An electric dipole consists of two equal and opposite charges (q and –q) separated by a distance (2a).
• The dipole moment is the product of either charge and the distance separating them.
• The electric field due to an electric dipole is inversely proportional to the cube of the distance from the centre of the dipole; this varies much more rapidly than the electric field due to a single charge.

1.11 Dipole in a Uniform External Field

• When a dipole is placed in a uniform electric field, it experiences a torque that tends to align the dipole with the field.
• However, the dipole experiences no net force.
• Torque=(dipole moment x electric field).

1.12 Continuous Charge Distribution

• Charges can be considered continuously distributed, rather than discrete points.
• Linear charge density (λ) is charge per unit length.
• Surface charge density (σ) is charge per unit area.
• Volume charge density (ρ) is charge per unit volume.

1.13 Gauss's Law

• Gauss's law relates the total electric flux through a closed surface to the total charge enclosed by the surface.
• It is a useful tool for calculating the electric field when dealing with symmetrical charge distributions.

This quiz focuses on the concepts of acceleration in electric fields and free fall under gravity, specifically involving electrons and protons. You will calculate acceleration values, explore the influence of electric fields, and examine the relationship between mass and gravitational effects. Test your understanding of these fundamental physics concepts!