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?

Because the electric field inside the cage is zero. 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?

In a hollow object, excess charges migrate to the outer surface, while in a solid object, they also migrate to the outer surface. Signup and view all the answers

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

Cavendish Signup and view all the answers

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

That the cork was strongly attracted to the outer surface of the can. 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?

It is inversely proportional to the square of the distance. Signup and view all the answers

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

Fe can be attractive or repulsive, while Fg is always attractive. Signup and view all the answers

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

Ignore the positive or negative signs when calculating magnitude, use them to determine direction. Signup and view all the answers

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

The 'field' concept. Signup and view all the answers

Which statement best describes an electric field?

It is the space surrounding a charge that exerts an electrostatic force on other charges. Signup and view all the answers

Which characteristic is NOT true of electric fields?

They are scalar fields. Signup and view all the answers

What determines the direction of a gravitational field?

The direction of gravitational force on a small test mass. Signup and view all the answers

How is the direction of an electric field determined?

By the direction of the electric force on a small imaginary positive test charge. Signup and view all the answers

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

The closer the field lines, the stronger the field. Signup and view all the answers

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

Field lines that are closer together. Signup and view all the answers

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

Tangent to the field line at that point. 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?

If the spacing is uniformly spread, the electric field is the same everywhere. Signup and view all the answers

What is the electric field strength inside a hollow conductor?

There is no electric field inside a hollow conductor. Signup and view all the answers

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

To insulate devices from outside electric fields. Signup and view all the answers

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

A force, the strength and direction of which depends on the magnitude and direction of the field 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?

3.61 N/C at 33.7 degrees below the right horizontal. 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?

18 cm 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?

52.1 N/C 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?

The electric field lines do not connect to the other charge for like charges, but do connect to the other charge for unlike charges. Signup and view all the answers

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

The EPE remains unchanged. Signup and view all the answers

What is the correct definition of electrical potential difference?

The change in electric potential energy per unit charge. Signup and view all the answers

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

The EPE increases. Signup and view all the answers

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

The GPE decreases. Signup and view all the answers

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

The work done is equal to the electric potential difference times the charge. 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?

2 eV Signup and view all the answers

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

m²/s² Signup and view all the answers

How is the gravitational potential difference calculated?

The change in gravitational potential energy per unit mass. Signup and view all the answers

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

eV is the energy gained by an electron across 1V, J is a fundamental unit. Signup and view all the answers

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

eV is not part of the SI metric system and causes inconsistencies in equations. Signup and view all the answers

What describes the electric field created between two parallel plates?

It is uniform except at the edges. 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?

It gains potential energy due to work done against the field. Signup and view all the answers

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

V = E * d Signup and view all the answers

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

N/C Signup and view all the answers

Which statement regarding equipotential lines is true?

They are perpendicular to electric field lines and indicate equal potential differences. Signup and view all the answers

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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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.