Electrokinetics and Electrostatics

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Questions and Answers

What phenomenon does electrokinetics primarily involve?

The thermal conductivity of materials

The motion of mass under gravity

The behavior of magnets in electric fields

The transport of electric charges (correct)

Which unit is commonly used to measure electric charge in the international system?

Ohm (Ω)

Ampere-hour (A h)

Volt (V)

Coulomb (C) (correct)

What happens to charges of the same sign when they interact?

They repel each other (correct)

They neutralize each other

They create a magnetic field

They attract each other

What term is used to describe the balance between positive and negative charges in ordinary matter?

Electrical neutrality Signup and view all the answers

Which of the following statements is true regarding the measurement of electric charge?

Charges can be measured using both positive and negative numbers Signup and view all the answers

Which material has the highest dielectric constant from the list provided?

Porcelain Signup and view all the answers

What type of materials are considered conductors?

Materials with a high number of free electrons Signup and view all the answers

Which of the following is a characteristic of insulating materials?

They prevent current flow. Signup and view all the answers

In metallic conductors, what causes the electric current to eventually stop?

The depletion of free electrons Signup and view all the answers

Which material is noted as the best conductor of electricity?

Silver Signup and view all the answers

In liquids, electric current consists of which types of particles?

Positive ions and negative ions Signup and view all the answers

What happens to charges +Q and -Q in a metallic conductor when placed at its ends?

Electrons will drift until reaching equilibrium Signup and view all the answers

What is the dielectric constant of air?

1.00059 Signup and view all the answers

What does Coulomb’s law describe about electric charges at rest?

The interaction is based on the product of the charges and inversely proportional to the square of the distance Signup and view all the answers

According to Coulomb's law, how do the electric forces exerted by two charges on each other behave?

They are equal and opposite forces Signup and view all the answers

What will the nature of the force be if two charges have the same sign?

The force will be repulsive Signup and view all the answers

What variable is included in the formula that is necessary to calculate the electric force between two point charges?

Distance of separation between the charges Signup and view all the answers

How is the resultant force calculated when a charge is subjected to multiple forces from two different charges?

By using vector addition based on the forces' directions and magnitudes Signup and view all the answers

What does the term 'vacuum permittivity' refer to in the context of Coulomb's law?

A constant that characterizes the strength of electric forces in vacuum Signup and view all the answers

In the context of Coulomb's law and electric fields, what is a test charge used for?

To determine the magnitude of the electric field at a point Signup and view all the answers

What happens to the force between two charges if the distance between them is doubled?

The force becomes one-fourth its original value Signup and view all the answers

What is the formula for calculating electrical power?

Power = Voltage x Current Signup and view all the answers

What does Joule’s Law relate to in an electrical context?

The heat produced by electric current Signup and view all the answers

In the context of Kirchhoff’s rules, what is defined as a closed path made up of successive network branches?

Loop Signup and view all the answers

According to the junction rule in Kirchhoff’s rules, what is a node?

The point where at least two branches meet Signup and view all the answers

Which of the following units is used to measure electrical power?

Watt Signup and view all the answers

When analyzing electric circuits, what does the branch refer to?

A set of dipoles carrying the same current Signup and view all the answers

What happens to electrical power as voltage increases while current remains constant?

Power increases Signup and view all the answers

What effect does power dissipation through a resistor primarily take the form of?

Heat energy Signup and view all the answers

What is the relationship between current density and the local electrostatic field in a conductor?

Current density is directly proportional to the electrostatic field. Signup and view all the answers

What does the term resistivity refer to in the context of a conductor?

A constant of proportionality unique to each material. Signup and view all the answers

Which equation relates the resistivity of a metallic conductor to its temperature?

$\rho(T) = \rho(T_0) + \alpha(T - T_0)$ Signup and view all the answers

How is conductivity defined in relation to resistivity?

Conductivity is the inverse of resistivity. Signup and view all the answers

What does the potential difference (p.d.d.) between the terminals of a generator measure?

The difference in positive and negative charges. Signup and view all the answers

According to Mathiessen's law, how does the resistance of a conductor change?

Resistance increases with temperature. Signup and view all the answers

Which of the following materials has a temperature coefficient of resistivity that is typically positive?

Copper Signup and view all the answers

What unit is used to express potential difference?

Volt Signup and view all the answers

What is the purpose of the balance condition in a galvanometer?

To ensure zero or null deflection Signup and view all the answers

Which equation represents the voltage across the resistor in the RC circuit?

$UR = R \frac{dq}{dt}$ Signup and view all the answers

When analyzing the charge of a capacitor at any instant, which variable is primarily affected by time?

Charge on the capacitor, q Signup and view all the answers

What method can be used to solve the first-order differential equation describing the capacitor's charge?

Separation of variables method Signup and view all the answers

What relationship is expressed by the balance condition for resistors in the bridge?

$\frac{R1}{R2} = \frac{R3}{R4}$ Signup and view all the answers

In a meter bridge configuration, the purpose of connecting resistors in loops is to apply which law?

Kirchhoff's loop rule Signup and view all the answers

What condition is used to derive the integration constants when solving the differential equation for an RC circuit?

Charge of capacitor when t = 0 Signup and view all the answers

In the context of capacitor charging, what does the term 'ddp' refer to?

Difference in potential Signup and view all the answers

Study Notes

Electrokinetics: Charges and Fields

Electrokinetics encompasses physicochemical and mechanical phenomena involving charge transport and effects of applied electric potentials.
Electric charges (symbol q) are fundamental to various phenomena. They are measured in Coulombs (C), and can have positive or negative signs.
Charges with the same sign repel, while opposite signs attract. Electrical neutrality describes a balance of positive and negative charges.
The elementary charge (e) is 1.6 x 10^-19 C.
Atoms comprise charged particles:
- Electrons (e) with charge -1.6 x 10^-19 C and mass 9.1 x 10^-31 kg.
- Protons (H+) with charge +1.6 x 10^-19 C and mass 1.67 x 10^-27 kg.

Electrostatics

Electrostatics studies stationary electric charges.
Electrification is the process of acquiring electric charge.
Point charges are dimensionless, like material points in mechanics.
Continuous charge distributions are macroscopic charges. Their infinitesimal charge (dq) is used in calculations.
Charge density (linear, surface, volume) quantifies charge per unit length, area, or volume respectively.

Coulomb's Law

Coulomb's law describes electrostatic force between stationary charges: Force is directly proportional to the product of the charges and inversely proportional to the square of the distance between them.
qq'/4πε₀r² (Force equation).
k = 1 / 4πε₀ = 9 x 10⁹ N⋅m²/C² (Coulomb's constant)
Force is attractive if charges have opposite signs and repulsive if charges have the same sign.

Electrical Field

The electrical field (E) is a vector quantity measuring the force on a positive test charge placed in the field. E = F/q.
Its SI unit is N/C.
The principle of superposition applies to electric fields, allowing calculation of net field from multiple charges.

Electric Potential

Electric potential (V), measured in volts (V), is scalar, representing electrical potential energy per unit charge (U/q)
The potential at a point due to a point charge Q is given by: V = Q / 4πε₀r.
The electrostatic potential energy (U_E) of a point charge q at a point in the electric field due to a point charge Q is given by U_E = qQ /4πε₀r.

Conductors in Electrostatic Equilibrium

Inside a conductor, the electric field is zero (E=0).
The potential inside is constant; it's an equipotential volume
All charges reside on the surface.

Capacitance

The capacitance (C) of an isolated conductor is proportional to its charge (Q) and inversely proportional to its voltage (V). Q = CV.
The SI unit of capacitance is the farad (F).

Capacitors

A capacitor is a device utilizing two conductors (armatures) separated by an insulator (dielectric). Its capacitance depends on the geometry.
Capacitance increases with the insertion of a dielectric medium (like glass, rubber, or air). C= kC_o, where k is the dielectric constant.

Electric Current and Current Density

Electric current (I) is the ordered movement of charged particles (e.g., electrons, ions, holes). Measured in amperes (A).
Current density (J). is the current per unit cross-sectional area of a conductor. J= I/A.
In a conductor, the current depends on the applied voltage (Ohm's Law: V = IR).

Resistors

Resistors oppose the flow of current within a circuit.
Resistors can be connected in series or parallel; series resistance add linearly Req= Σ R_i While parallel resistance are calculated as 1/Req= Σ (1/R_i)
The resistance depends on material characteristics .

Circuit Laws

Kirchhoff junction rule: Σ I = 0 at any junction,.
Kirchhoff's loop rule: Σ V = 0 around any closed loop.

Generators

Generators provide the electrical power supply within a circuit.
Voltage sources (e.g., batteries) provide a constant voltage regardless of current.
Current sources provide a constant current regardless of voltage.

Wheatstone Bridge

The Wheatstone bridge is a circuit for measuring unknown resistances.
It utilizes the balance condition R₁/ R₂ = R₃/ R₄ to determine the unknown resistance (R) based upon known values for the other three resistors.

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Description

This quiz explores the fundamentals of electrokinetics and electrostatics, including the nature of electric charges, their interactions, and the principles of charge transport. Learn about the properties of charges, their measurements, and the significance of electric neutrality in various phenomena.