Electrical & Magnetic Fields Summary

Comprehensive question-and-answer revision flashcards covering electrostatics, Coulomb's law, electric fields and flux, magnetism, Ampère's law, Ohm's law, and Kirchhoff's laws.

What is the definition of electrostatic?

The study of the properties and interaction of electric charges which are fixed with respect to the internal frame of reference chosen for this study.

How is an electrical charge defined?

The property of matter that causes electricity.

When does an electrical discharge occur?

When static electricity moves from one object to another, removing charges.

What does the Law of Conservation of Electric Charge state?

The algebraic sum of the electric charges remains constant in a closed system.

How does the behavior of electrons and protons support the conservation of electric charge?

Electrons and protons remain constant; they neither increase nor decrease, and only move from one object to another, causing a transfer of charge.

What does Coulomb's Law state regarding point charges?

The force $F$ of electrostatic interaction between two point electric charges $q_1$ and $q_2$ in a vacuum is directly proportional to the product of the charges and inversely proportional to the square of the distance $r$ between them.

What is the mathematical equation for Coulomb's Law?

$$F = k\frac{q_1 q_2}{r^2} = \frac{q_1 q_2}{4\pi \varepsilon_0 r^2}$$

What is an electric field?

An invisible force field caused by an electric charge; an alteration in the space (air or vacuum) around the charge resulting in an electric force felt by electric charges placed close to one another.

What is electric field intensity and how is it defined?

The strength of the electric field in the space surrounding a source charge, defined as the electric force experienced by a unit charge.

What is the formula for the electric field $E$?

$$E = \frac{F}{q} = \frac{q}{4\pi \varepsilon_0 r^2} = \frac{k q}{r^2}$$

What are the SI units and dimensional formula of electric field intensity?

The SI units are volt/meter ($\text{V/m}$) or newtons/coulomb ($\text{N/C}$), and the dimensional formula is $[M\,L\,T^{-3}\,I^{-1}]$.

What are electric lines of force?

Imaginary lines drawn around a charge, the tangent at which gives the electric field vector, with arrows signifying the direction.

In an electric dipole, how do the field lines behave?

Lines come out of the positive charge and terminate into the negative charge.

How is the direction of an electric field defined?

The direction a positive charge moves under the influence of another charge.

What is the principle of superposition of electric fields?

The field at a point from several charges is the vector sum of the field of each charge on a unit charge: $E = E_1 + E_2 + E_3$.

What is electric field flux and its mathematical formula?

The number of field lines passing through a certain area in space, calculated as the dot product of the electric field and the area vector: $\Phi = \mathbf{E} \cdot \mathbf{A} = E A \cos(\theta)$.

Which materials can a magnet attract?

Objects made of iron, steel, cobalt, and nickel.

Which part of a magnet has the strongest attraction force?

The pole of the magnet.

Why does Earth have a magnetic field?

Due to the huge iron deep in its core.

What discovery was made by Oersted in 1820?

An electric current flowing in a straight wire affects a compass needle placed next to it, demonstrating that the current creates a magnetic field.

What does Ampère's Law state?

The circulation of the magnetic field around a closed path is proportional to the electric current enclosed by that path.

What is the formula for the magnetic field $B$ around a straight current-carrying wire derived from Ampère's Law?

$$\oint \mathbf{B} \cdot d\mathbf{l} = \mu_0 I \rightarrow B = \frac{\mu_0 I}{2\pi r}$$

What does Ohm's Law state and what is its equation?

The voltage across a component is equal to the product of the current flowing through it and the resistance of the component: $V = I \times R$.

Upon what conservation principles are Kirchhoff's Laws based?

The conservation of electric charge and energy in an electrical circuit.

What does Kirchhoff's Current Law (KCL) state?

The sum of currents entering a junction is equal to the sum of currents leaving the junction: $\sum I_{\text{in}} = \sum I_{\text{out}}$.

What does Kirchhoff's Voltage Law (KVL) state?

The sum of voltage in a loop is equal to zero: $\sum V = 0$.

What is the value and unit of the permittivity of free space ($\varepsilon_0$)?

$$8.85 \times 10^{-12}\,\text{C}^2\,\text{N}^{-1}\,\text{m}^{-2}$$

What is the value and unit of Coulomb's constant ($k$)?

$$k = \frac{1}{4\pi \varepsilon_0} = 8.99 \times 10^9\,\text{N}\cdot\text{m}^2/\text{C}^2$$

What is the value and unit of the permeability of free space ($\mu_0$)?

$$4\pi \times 10^{-7}\,\text{T}\cdot\text{m}/\text{A}$$