Electrostatics and Coulomb's Law Overview
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Questions and Answers

What did Priestly primarily infer from Franklin’s observation of a cork inside a charged metal can?

  • That neutral objects always experience electric forces.
  • That electric forces are shielded by metal.
  • That electric fields resemble gravitational fields within hollow objects. (correct)
  • That electric forces are stronger than gravitational forces.

What is the primary reason excess charges distribute themselves on the outer surface of a hollow conducting object?

  • To minimize the electrostatic repulsion between charges.
  • To ensure an even distribution of the charge across both the inner and outer surfaces.
  • To maximize the gravitational force acting on the charges.
  • To achieve static equilibrium and maximize the distance between charges due to repulsion. (correct)

What is the net electric field inside a hollow conducting object, regardless of its shape?

  • The vector sum of all individual electric fields is always greater than zero.
  • The net electric field is zero. (correct)
  • The electric field is always the same as the external field.
  • The electric field depends on the amount of charge on the outer surface.

Why is a person inside a Faraday cage protected from strong external electrical charges?

<p>Because the electric field inside the cage is zero. (D)</p> Signup and view all the answers

What is a key difference between the distribution of excess charges inside a hollow conducting object, and a solid conducting object?

<p>In a hollow object, excess charges migrate to the outer surface, while in a solid object, they also migrate to the outer surface. (D)</p> Signup and view all the answers

The work of which scientist was used by Charles Coulomb when he developed his law for electrostatic forces?

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

What was the key observation made by Franklin regarding a neutral cork near a charged metal can?

<p>That the cork was strongly attracted to the outer surface of the can. (A)</p> Signup and view all the answers

According to Coulomb's Law, how does the electrostatic force between two charged particles change with the distance between them?

<p>It is inversely proportional to the square of the distance. (B)</p> Signup and view all the answers

Which of the following is a key difference between electrostatic force (Fe) and gravitational force (Fg)?

<p>Fe can be attractive or repulsive, while Fg is always attractive. (D)</p> Signup and view all the answers

When calculating the magnitude of the electrostatic force, what should be considered regarding the charges?

<p>Ignore the positive or negative signs when calculating magnitude, use them to determine direction. (A)</p> Signup and view all the answers

What concept did Michael Faraday introduce to explain 'action at a distance'?

<p>The 'field' concept. (D)</p> Signup and view all the answers

Which statement best describes an electric field?

<p>It is the space surrounding a charge that exerts an electrostatic force on other charges. (B)</p> Signup and view all the answers

Which characteristic is NOT true of electric fields?

<p>They are scalar fields. (D)</p> Signup and view all the answers

What determines the direction of a gravitational field?

<p>The direction of gravitational force on a small test mass. (C)</p> Signup and view all the answers

How is the direction of an electric field determined?

<p>By the direction of the electric force on a small imaginary positive test charge. (A)</p> Signup and view all the answers

What does the spacing between field lines indicate about the strength of an electric field?

<p>The closer the field lines, the stronger the field. (A)</p> Signup and view all the answers

In an electric field, what indicates a stronger field strength?

<p>Field lines that are closer together. (D)</p> Signup and view all the answers

What is the direction of the electric force on a charge placed within an electric field?

<p>Tangent to the field line at that point. (C)</p> Signup and view all the answers

How does the spacing of electric field lines relate to the magnitude of the electric field for parallel plates?

<p>If the spacing is uniformly spread, the electric field is the same everywhere. (A)</p> Signup and view all the answers

What is the electric field strength inside a hollow conductor?

<p>There is no electric field inside a hollow conductor. (C)</p> Signup and view all the answers

What is the purpose of housing electronic devices in hollow conductors?

<p>To insulate devices from outside electric fields. (A)</p> Signup and view all the answers

If a charge is placed in an existing electric field, what does the charge experience?

<p>A force, the strength and direction of which depends on the magnitude and direction of the field (C)</p> Signup and view all the answers

Two charges, A and B, create fields at point P. If field A is 3.00 N/C [right] and field B is 2.00 N/C [down], what is the net electric field at P?

<p>3.61 N/C at 33.7 degrees below the right horizontal. (A)</p> Signup and view all the answers

A sphere with a diameter of 4.0 cm has 2.4 x 10^20 excess electrons. What is the distance (r) to use when calculating the electric field at 16 cm from the sphere's surface?

<p>18 cm (B)</p> Signup and view all the answers

A 60 µC charge experiences an acceleration of 1.25x10^4 m/s² in an electric field. If the mass of the charge is 0.25 mg, what is the electric field strength at that point?

<p>52.1 N/C (D)</p> Signup and view all the answers

What would be the key difference when picturing the electric fields lines around like charges, compared to those around unlike charges?

<p>The electric field lines do not connect to the other charge for like charges, but do connect to the other charge for unlike charges. (B)</p> Signup and view all the answers

If a positive charge moves perpendicular to an electric field, what happens to its electric potential energy (EPE)?

<p>The EPE remains unchanged. (D)</p> Signup and view all the answers

What is the correct definition of electrical potential difference?

<p>The change in electric potential energy per unit charge. (A)</p> Signup and view all the answers

An alpha particle is moved against the electric field. What is true of its electric potential energy (EPE)?

<p>The EPE increases. (B)</p> Signup and view all the answers

Which of the following accurately describes gravitational potential energy (GPE) when an object moves towards the Earth?

<p>The GPE decreases. (C)</p> Signup and view all the answers

What is the relationship between the work done against electric forces and the electric potential difference?

<p>The work done is equal to the electric potential difference times the charge. (D)</p> Signup and view all the answers

An electron accelerates across a potential difference of 2 volts. How much energy, in electron-volts (eV), does it gain?

<p>2 eV (A)</p> Signup and view all the answers

What unit is used to measure the change in gravitational potential energy per unit mass?

<p>m²/s² (B)</p> Signup and view all the answers

How is the gravitational potential difference calculated?

<p>The change in gravitational potential energy per unit mass. (A)</p> Signup and view all the answers

What is the key difference between electron-volts (eV) and Joules (J) in the context of energy?

<p>eV is the energy gained by an electron across 1V, J is a fundamental unit. (B)</p> Signup and view all the answers

Why is it crucial to use Joules instead of electron-volts (eV) in physics formulas?

<p>eV is not part of the SI metric system and causes inconsistencies in equations. (C)</p> Signup and view all the answers

What describes the electric field created between two parallel plates?

<p>It is uniform except at the edges. (A)</p> Signup and view all the answers

What happens to a proton when it is moved from point A to point B in an electric field?

<p>It gains potential energy due to work done against the field. (D)</p> Signup and view all the answers

How is electric potential difference (V) related to electric field strength (E) and distance (d)?

<p>V = E * d (B)</p> Signup and view all the answers

What is the appropriate unit of measurement for electric field strength?

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

Which statement regarding equipotential lines is true?

<p>They are perpendicular to electric field lines and indicate equal potential differences. (A)</p> Signup and view all the answers

Flashcards

Franklin's Observation

The observation that a neutral cork experiences attraction to the outside surface of a charged metal can, but no attraction when lowered inside the can.

Faraday's Cage

A hollow conducting object, where charges align themselves on the outer surface to create a zero net force inside.

Static Equilibrium in Conductors

The distribution of charges on a conductor, where repelling charges spread out and accumulate on the outer surface, resulting in a zero electric field inside.

Zero Electric Field Inside Hollow Conductors

The phenomenon where the electric field inside a hollow conductor is always zero, irrespective of the shape of the object.

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Torsion Balance

A device used by Coulomb to measure the relationship between electrostatic and gravitational forces, similar to Cavendish's device for measuring G.

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Coulomb's Law

The force of attraction or repulsion between charged objects, proportional to the product of the charges and inversely proportional to the square of the distance between them.

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Conductivity

The ability of a material to conduct electricity, determined by the ease with which charges can move through it.

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Electrostatic vs. Gravitational Forces

Electrostatic forces are much stronger than gravitational forces. They can be attractive or repulsive, while gravity is always attractive.

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Electric Field

The region surrounding a charged object where other charges experience a force.

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Vector Field

A field that has both magnitude and direction, like the electric force on a test charge placed in the field.

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Electric Field Lines

The strength of the electric field is represented by the density of field lines. Closer lines indicate a stronger field.

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Electric Field Strength and Distance

The electric field decreases in strength as the distance from the charge increases.

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Gravitational Field

A region where objects experience a force of attraction towards a mass.

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Scalar Field

A field that has only magnitude, like temperature, pressure, or density.

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Electric Field Direction

The electric force on a small positive test charge placed in an electric field indicates the direction of the field.

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Parallel Plate Capacitor

A uniform electric field between two parallel plates is created by connecting them to a battery, where the field strength (E) is constant except at the edges. This means the electric field is the same everywhere inside the plates.

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Equipotential Lines

Equipotential lines are lines of equal potential difference, perpendicular to the electric field lines, and parallel to the plates. The difference in potential is what matters.

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Proton Movement and Potential Energy

Moving a proton from a point of lower potential to a point of higher potential requires work to be done against the electric field, resulting in a gain of potential energy. The reverse movement results in a loss of potential energy.

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Electric Field Calculation

The electric field strength (E) can be calculated as the potential difference (V) across the plates divided by the distance (d) between the plates: E = V/d. This formula only applies if the electric field is uniform, such as between parallel plates.

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Voltmeter and Potential Difference

A voltmeter is used to measure the potential difference across two charged plates.

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Electric Field Strength

The strength of an electric field at a point is defined as the force per unit charge experienced by a small test positive charge placed at that point.

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Electric Field Lines Density

Electric field lines are closer together where the field is stronger and farther apart where the field is weaker.

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Electric Field in Conductors

A hollow conductor, such as a metal shell, shields the interior from external electric fields. No electric field exists inside the conductor.

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Direction of Electric Field

The electric field at any point is tangent (perpendicular) to the electric field line at that point.

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Net Electric Field

The net electric field from multiple charges is the vector sum of the individual electric fields created by each charge.

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Electric Field Between Plates

The electric field between two oppositely charged parallel plates is uniform, meaning the field strength is constant throughout the space between the plates.

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Sources of Electric Fields

Electric fields are created by electric charges, and the strength of the field depends on the magnitude and distribution of these charges.

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Force in an Electric Field

The force experienced by a charge placed in an electric field is proportional to the strength of the field and the magnitude of the charge.

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Calculating Electric Field Strength

The electric field strength at a point in space is calculated using Coulomb's law and the distance from the source charge.

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Electric Potential Energy (EPE)

The energy a charged object possesses due to its position in an electric field.

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Gravitational Potential Difference

The change in gravitational potential energy per unit mass. It is the work done against gravity to move an object from one point to another.

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Electrical Potential Difference (∆V)

The change in electric potential energy per unit charge. It is the work needed to move a charge through an electric field.

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Electron Volt (eV)

A unit of energy equal to the energy gained by an electron accelerating through a potential difference of one volt.

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Gravitational Potential Energy (GPE)

This is the energy an object has due to its position in a gravitational field.

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EPE in relation to Potential

If a positive charge is moved towards a point with a higher electrical potential, its EPE increases.

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EPE and Motion Perpendicular to Field

No work is done, and therefore no change in EPE occurs, if a charge moves perpendicular to an electric field.

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E = qV

The formula relating energy (E), charge (q), and potential difference (V), which is crucial for understanding potential energy and its applications.

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Charge Movement in Electric Field

If a positively charged object is released within an electric field, it will accelerate towards the lower potential region.

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Electron Volt (eV) Conversion

1 eV is equivalent to 1.60 × 10^-19 Joules.

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Study Notes

Electrostatics - Historical Development

  • Franklin noted that a neutral cork attracted to the outside of a charged metal can, but not the inside
  • Priestly reasoned that the lack of net force inside the metal can was similar to no net gravity inside a hollow planet
  • Shielding (Faraday's Cage): Charges align on the surface to balance repulsive forces, resulting in zero net force inside a hollow conductor
  • Excess charges move to achieve static equilibrium on the outer surface of a hollow conductor
  • No excess charge on the inner surface of a hollow conductor, regardless of shape

Coulomb's Law

  • Coulomb tested the relationship between electrostatic and gravitational forces using a torsion balance similar to Cavendish's device
  • Coulomb's Law: The electrostatic force is directly proportional to the charges and inversely proportional to the square of the distance between them

Coulomb's Law - Considerations

  • Electrostatic forces (F) can be attractive or repulsive, unlike gravitational forces (which are always attractive)
  • When calculating the electrostatic force, do not include positive/negative signs for charge (q)
  • Use vector addition to find the resultant force (considering attraction or repulsion)

Example 1

  • Two equally charged particles with an attractive force of 3.56 x 104 N, separated by 0.34 cm, are given.
  • Find the charge on each particle

Example 2

  • Multiple charges (given as μC) are arranged with distances (given in meters).
  • Determine the net electrostatic force on a specific charge.

Electric Fields

  • Faraday developed the field concept, solving the action-at-a-distance problem
  • A field is a region of influence around an object that causes a force on another object
  • Gravitational field: Space around a mass; other masses experience attraction
  • Electric field: Space surrounding a charge; other charges experience electrostatic force (attraction/repulsion)

Electric Field Characteristics

  • Can be produced by positive or negative charges
  • Strength decreases with distance
  • Vector field (like gravitational fields)

Picturing Electric Fields

  • Field strength indicated by spacing between field lines (closer = stronger)
  • Electric fields around like charges spread out
  • Electric fields around unlike charges point toward each other

Electric Field Lines and Conductors

  • No electric field inside a hollow conductor (shielding principle)

Electric Field Strength

  • Strength (intensity) used for radially outward fields around source charges

Example 3

  • Three charges are lined in a plane.
  • Charge A and Charge B are given,
  • Find the position of an unknown charge C in equilibrium.

Example 4

  • Multiple charges are given with details like position on plane, charge, distance etc...

Comparing Gravitational and Electrical Differences

  • Gravitational potential energy (GPE) changes with position in a gravitational field
  • Electrical potential energy (EPE) changes with position in an electric field
  • Potential difference (electrical/gravitational) is the change in energy per unit charge/mass between two points

Electric Potential

  • Potential difference is the work done per unit charge in moving a charge between two points in an electric field

Electron Volts (eV)

  • Unit of energy
  • Energy an electron gains or loses after accelerating across one volt.
  • 1 eV = 1.60 x 10-19 J

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Physics 30 Electrostatics Lesson 2 Coulomb's Law PDF

Description

Explore the historical development of electrostatics and understand Coulomb's Law through its defining principles. Delve into the concepts of charge distribution in conductors, shielding effects, and the relationship between electrostatic and gravitational forces. This quiz will test your knowledge on these fundamental principles of physics.

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