Electricity & Magnetism Class Notes

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Questions and Answers

What is the scalar product of two vectors ~a and ~b making a 90° angle with each other?

  • ab
  • 1
  • 0 (correct)
  • cos(90°)

If vectors ~a = (1, 2) and ~b = (-1, 3), what is the value of the scalar product ~a · ~b?

  • 3
  • 5 (correct)
  • 7
  • 0

In the formula for scalar product, what does the term 'cos(φ)' represent?

  • Magnitude of the result vector
  • Sum of the components of the vectors
  • Magnitude of the dot product
  • Angle between the two vectors (correct)

Which statement is true regarding the scalar product of two vectors?

<p>It is maximized when the vectors are parallel. (C)</p> Signup and view all the answers

Which of the following scenarios would yield a scalar product of zero?

<p>Vectors that are perpendicular (B)</p> Signup and view all the answers

When calculating the scalar product using components, which operation is performed?

<p>Multiplication of corresponding components followed by addition (C)</p> Signup and view all the answers

What happens to the work done when the force vector is perpendicular to the displacement vector?

<p>No work is done. (A)</p> Signup and view all the answers

In three-dimensional space, what is a key requirement for the coordinate system when calculating vector operations?

<p>It must allow rotation but not reflection. (D)</p> Signup and view all the answers

What does the ratio $F_0 / q_0$ represent in the context of electric fields?

<p>The electric field created by the primary charge (C)</p> Signup and view all the answers

Which of the following units is equivalent to the electric field strength $E$?

<p>N/C (A)</p> Signup and view all the answers

In the given expression for the force $F_0 = k rac{q imes q_0}{r^2}$, what does the variable $k$ represent?

<p>The electric constant (Coulomb's constant) (A)</p> Signup and view all the answers

What does the integration in the expression for $F_x$ ultimately demonstrate?

<p>The cumulative effect of all point charge forces (A)</p> Signup and view all the answers

What role does the angle $θ$ play in the expression for $dF_x$ in electric field calculations?

<p>It determines the direction of the force (B)</p> Signup and view all the answers

Which statement best describes the behavior of the electric field as given by the ratio $F_0/q_0$?

<p>It remains constant regardless of the probe charge. (A)</p> Signup and view all the answers

When deriving the electric field from the force equation, what does the notation $E$ represent?

<p>The electric field vector (D)</p> Signup and view all the answers

What is the significance of the integration limits in the expression for $F_x$?

<p>They define the range of theta values contributing to the force (C)</p> Signup and view all the answers

What does electric flux represent?

<p>The number of electric field lines crossing a surface (D)</p> Signup and view all the answers

How is the flux through a small surface element defined?

<p>Flux is determined by the electric field density and area vector (D)</p> Signup and view all the answers

What happens to the electric flux when multiple charges are present?

<p>Fluxes add together as scalars (B)</p> Signup and view all the answers

In Gauss's law, what does the term $Φ = \frac{q_{enc}}{\epsilon_0}$ signify?

<p>The electric flux through a closed surface equals the enclosed charge divided by the permittivity (B)</p> Signup and view all the answers

What is true about the nature of electric flux?

<p>Electric flux is a scalar quantity (D)</p> Signup and view all the answers

What is the expression for the electric flux Φ through a Gaussian surface centered at a charge?

<p>$4 ext{Ï€}r^2E$ (C)</p> Signup and view all the answers

What is necessary to evaluate the total electric flux through a closed surface?

<p>The net charge enclosed inside the surface (B)</p> Signup and view all the answers

Which of the following is NOT true regarding the flux through a surface?

<p>Flux is always a positive scalar value (D)</p> Signup and view all the answers

How does the field E outside a uniformly charged spherical shell compare to that of a point charge?

<p>E is the same as that of a point charge (B)</p> Signup and view all the answers

Which mathematical expression defines electric flux through a surface?

<p>Φ = E · A (B)</p> Signup and view all the answers

What role does symmetry play in applying Gauss' Theorem?

<p>It allows for the selection of an appropriate Gaussian surface. (A)</p> Signup and view all the answers

For a spherical shell with radius R and total charge Q, what is the charge enclosed when using a Gaussian surface with radius r inside the shell?

<p>0 (D)</p> Signup and view all the answers

What is the correct expression for the electric field E derived from Gauss' Theorem for a point charge q?

<p>$ rac{q}{4 ext{π} ext{ε}_0 r^2}$ (C)</p> Signup and view all the answers

What happens to the electric field E inside a uniformly charged spherical shell?

<p>E is zero (B)</p> Signup and view all the answers

What is necessary when applying Gauss' Theorem to ensure accurate results?

<p>Choosing the right Gaussian surface that reflects symmetry (B)</p> Signup and view all the answers

When can we postulate Gauss' Theorem as a fundamental law?

<p>By considering symmetry and field behavior (B)</p> Signup and view all the answers

What is the magnitude of the electric field from the dipole at the observation point when side a = 3.0 mm?

<p>$1.0 \times 10^6 \text{ N/C}$ (D)</p> Signup and view all the answers

How does the direction of the electric field from the dipole at the observation point compare to the arrangement of the charges?

<p>From positive to negative charges (C)</p> Signup and view all the answers

In the case of two identical positive charges, what form does the resulting electric field take?

<p>A vector pointing up (C)</p> Signup and view all the answers

What principle allows the reconstruction of electric fields from known charge distributions?

<p>Superposition principle (D)</p> Signup and view all the answers

What is the relationship between the distance from the charges and the magnitude of the electric field?

<p>Inversely proportional to the square of the distance (A)</p> Signup and view all the answers

What happens if both charges of the dipole are replaced by negative charges?

<p>The electric field inverts direction (B)</p> Signup and view all the answers

What happens to the electric field if the separation distance between the charges L decreases?

<p>Electric field strength increases (D)</p> Signup and view all the answers

What is the result of treating a distributed charge as a point charge?

<p>Allows integration to find the total field (A)</p> Signup and view all the answers

What is the electric field E for a point outside a uniformly charged non-conducting surface with charge density σ?

<p>$\frac{2σ}{\varepsilon_0}$ (C)</p> Signup and view all the answers

What value of the electric field E is obtained inside a uniformly charged non-conducting surface?

<p>$0$ (C)</p> Signup and view all the answers

According to Gauss's Law, what is the relationship between the electric flux Φ through a surface and the enclosed charge Q_enc?

<p>$Φ = \frac{Q_{enc}}{\varepsilon_0}$ (A)</p> Signup and view all the answers

What effect does the distance from the plane have on the magnitude of the electric field created by it?

<p>It remains constant regardless of distance. (A)</p> Signup and view all the answers

For two parallel charged plates, what is the resulting electric field between them?

<p>$\frac{2σ}{\varepsilon_0}$ (D)</p> Signup and view all the answers

What is represented by the variable A in the equations related to electric flux and enclosed charge?

<p>The area of the Gaussian surface. (D)</p> Signup and view all the answers

If the charge density σ is increased, how does it affect the electric field E created by a charged plane?

<p>E increases proportionally. (C)</p> Signup and view all the answers

In the formula $E = \frac{σ}{2\varepsilon_0}$ for a charged plane, what does the term ε₀ represent?

<p>The permittivity of free space. (D)</p> Signup and view all the answers

Flashcards

Scalar (dot) product of vectors

A mathematical operation that combines two vectors and results in a scalar value. It is defined as the product of the magnitudes of the two vectors and the cosine of the angle between them.

Scalar product of orthogonal vectors

The scalar product of two vectors is zero when they are perpendicular to each other. This is because the cosine of 90 degrees is zero.

Finding the angle between two vectors

The angle between two vectors can be calculated using the scalar product and the magnitudes of the vectors. The formula involves dividing the scalar product by the product of the magnitudes.

Work done by a force

The work done by a force on an object is equal to the scalar product of the force and the displacement of the object.

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Vector (cross) product of vectors

A vector product (also known as cross product) is a binary operation on two vectors in three-dimensional space that results in a vector perpendicular to both input vectors.

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Right-hand coordinate system

In a three-dimensional space, a right-hand coordinate system is defined as a system where the thumb points in the direction of the resulting vector when the fingers curl from the first vector to the second vector.

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Magnitude of the cross product

The magnitude of the cross product of two vectors is equal to the product of their magnitudes and the sine of the angle between them.

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Cross product of parallel vectors

The cross product of two parallel vectors is a zero vector. This is because the sine of 0 degrees is zero.

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Electric Field (E)

The force exerted by a primary charge (q) on a small probe charge (q0) divided by the value of the probe charge. It describes the electric influence of the primary charge at a specific point in space.

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Electric field due to a point charge

The electric field at a point in space due to a single stationary point charge is determined by Coulomb's Law and is directly proportional to the magnitude of the charge and inversely proportional to the square of the distance from the charge.

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Unit of Electric Field

The unit of electric field strength is Newton per Coulomb (N/C). This represents the force exerted on a charge of one Coulomb in the field.

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Coulomb's Law

The electric force between two point charges is directly proportional to the product of the charges and inversely proportional to the square of the distance between them.

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Force on a test charge in an electric field

A small test charge placed in an electric field will experience a force due to the field. This force is proportional to the magnitude of the test charge and the strength of the electric field.

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Vector nature of electric field

The electric field created by a point charge can be described by a vector quantity. This vector represents both the magnitude and direction of the electric force at a point in space.

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Electric field as a characteristic of the source charge

The ratio of the force experienced by a probe charge (q0) to the value of the probe charge (q0) is a characteristic of the primary charge (q) and independent of the probe charge. This ratio defines the electric field.

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Inverse square law in electric field

The electric field strength created by a point charge decreases with increasing distance from the charge. This inverse square relation is a result of the geometric spreading of the field.

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Electric Field of a Dipole (Axial)

The electric field produced by a dipole at a point a distance 'L' away from each charge and along the dipole's axis.

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Electric Field of a Dipole (Equatorial)

The electric field produced by a dipole at a point a distance 'L' away from each charge and perpendicular to the dipole's axis.

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Superposition Principle

A method to calculate the electric field generated by any charge distribution by treating each infinitesimally small element of the distribution as a point charge and summing the contributions of all these point charges.

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Charge Distribution (Continuous)

The process of dividing a continuous charge distribution into infinitesimally small elements, each acting as a point charge, to calculate the electric field generated by the distribution.

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Electric Field (Two Identical Charges)

The electric field due to two identical positive charges at a point equidistant from both charges.

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Displacement Vector (Electric Field)

A vector representing the change in position or displacement of a charged particle in an electric field.

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Net Electric Field

The electric field at a specific point in space due to a collection of charges, calculated by summing the electric fields produced by each individual charge.

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Electric Field (Dipole)

The electric field produced by a dipole, characterized by its unique directional and magnitude properties.

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Electric Flux

The number of electric field lines passing through a given surface. It's a scalar quantity measured in units of N⋅m²/C.

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Area Vector

The vector representing the area of a surface, with its direction perpendicular to the surface.

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Flux through a surface element

The change in electric flux through a small surface element. It's the product of the electric field component perpendicular to the surface and the area of the element.

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Total Flux through a closed surface

The total electric flux passing through a closed surface. Calculated by integrating the dot product of the electric field and the area vector over the entire surface.

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Gauss's Law

The electric flux through a closed surface is proportional to the net electric charge enclosed within the surface. The proportionality constant is 1/ε₀, where ε₀ is the permittivity of free space.

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Electric field line density

The electric field lines are denser in areas where the electric field strength is higher.

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Electric Field Strength

The force per unit charge experienced by a test charge placed in an electric field.

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Gaussian Surface

An imaginary surface used to calculate the electric flux. It can be any shape, but it's often chosen to simplify calculations.

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Electric Field Inside a Uniformly Charged Sphere

The electric field inside a uniformly charged sphere is zero. This is because the charges distribute symmetrically, canceling out the field at every point inside.

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Electric Field Outside a Uniformly Charged Sphere

The electric field outside a uniformly charged sphere is the same as if all the charge were concentrated at the center of the sphere.

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Electric Field Due to a Charged Plane

A non-conducting plane with uniform charge density (σ) creates an electric field that is perpendicular to the plane and has a constant magnitude of σ/(2ε0).

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Electric Field Between Parallel Plates

The electric field between two parallel charged plates is uniform and its magnitude is equal to the charge density (σ) divided by the permittivity of free space (ε0).

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Coulomb (C)

The unit of charge is the Coulomb (C). It's the fundamental unit for measuring the amount of electric charge.

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What is Gauss's Theorem (GT)?

Gauss's Theorem (GT) states that the total electric flux through a closed surface is proportional to the enclosed electric charge.

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How are Coulomb's Law and Gauss's Theorem related?

Coulomb's Law describes the force between two point charges, while Gauss's Theorem relates the electric flux through a closed surface to the enclosed charge. Both laws are fundamental to understanding electromagnetism.

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Explain Gauss's Theorem in simple terms using an analogy?

It is a mathematical relationship between electric flux and the enclosed charge in a closed surface. It's similar to saying the total amount of water flowing out of a pipe is determined by the amount of water inside the pipe.

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Why is Gauss's Theorem useful for calculating electric fields?

Gauss's Theorem can be used to calculate the electric field for continuous charge distributions with a high degree of symmetry, such as a sphere or a cylinder.

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Does GT derive Coulomb's Law or vice-versa?

The GT is used to derive Coulomb's Law, demonstrating that both concepts are strongly interconnected.

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What is the key to choosing a good Gaussian surface?

The Gaussian surface must be chosen such that the electric field is constant and perpendicular to the surface. This maximizes the simplicity of the calculations.

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What is the electric field inside a charged spherical shell?

The electric field inside a charged spherical shell is zero. This is because the enclosed charge is zero within the shell, according to Gauss's Theorem.

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What is the electric field outside a charged spherical shell?

For a charged spherical shell, the electric field outside the shell is the same as if all the charge was concentrated at the center of the sphere. This is a consequence of Gauss's Theorem and the radial symmetry of the charge distribution.

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Study Notes

Electricity & Magnetism Lecture Notes

  • These notes are supplementary to the in-class lectures, not a replacement.
  • They may contain less or more information than the lectures.
  • Not all formulas needed for exams are included.
  • No up-to-date administrative information (schedule changes, assignments, etc.) is included.
  • Typos should be reported to [email protected].
  • All notes will be in a single file.
  • Graphics may be intentionally unfinished for in-class discussion.
  • Preview topics can be skipped initially, but are beneficial for future learning.
  • Advanced topics will not appear on exams.

Contents

  • Introduction: Covers vectors (single, addition, scalar product, vector product), and fields.
  • Electric Charge: Discusses notations, units, superposition, quantization, conservation, Coulomb's Law, and superposition of forces.
  • Electric Field: Explains field due to a point charge (definition, units, vector fields, and field lines), field due to several charges (definition, force on a charge in a field, superposition of fields, electrostatic field lines (EFL), continuous charge distribution).
  • Gauss Theorem: Covers quantification of field lines, deformations of the Gaussian surface, definition of flux, Gauss theorem, applications (charged spherical shell, uniformly charged sphere, etc.), and a metal conductor analysis.
  • Electrostatic Potential (EP): Defines EP, units, work and energy in electrostatic fields, interaction of two charges, potential due to a point charge, and reactions of charges to electrostatic and other forces.
  • Properties of a Conductor in Electrostatics: Discusses properties of conductors in electrostatics (field, charge, potential).
  • Capacitance: Covers definitions, units, isolated sphere, spherical capacitor, parallel-plate capacitor, capacitor with a dielectric, a capacitor and a battery, energy, and connections of several capacitors.
  • Current: Introduces definitions, units, and resistance of a wire (including its relation to field).
  • Discusses various aspects of power
  • Circuits: Describes reduction methods, real batteries, the potential method, multiloop circuits, and Kirchhoff's equations.
  • Dielectrics: Detailed discussion of dielectric properties.
  • Provides examples with numerical calculations for different cases and situations showing how to apply the concepts learned from the previous chapters.

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