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Questions and Answers
What are the SI units for the electric field vector E?
What are the SI units for the electric field vector E?
- Newtons per coulomb (N/C) (correct)
- Joules per meter (J/m)
- Volts per meter (V/m)
- Coulombs per newton (C/N)
The electric field produced by a test charge is considered when determining the net electric field at a location.
The electric field produced by a test charge is considered when determining the net electric field at a location.
False (B)
A negative charge is placed in an electric field pointing due east. In what direction does the electric force on the charge point?
A negative charge is placed in an electric field pointing due east. In what direction does the electric force on the charge point?
West
The electric force on a charge is given by the formula F = q______
The electric force on a charge is given by the formula F = q______
If the electric field is known at a point, the force on any charged particle placed at that point can be calculated using which equation?
If the electric field is known at a point, the force on any charged particle placed at that point can be calculated using which equation?
The direction of the electric field created by a negative point charge is radially outward from the charge.
The direction of the electric field created by a negative point charge is radially outward from the charge.
What is an electric dipole?
What is an electric dipole?
The principle that the total electric field at a point is the vector sum of the electric fields of all the charges is called the ______ principle.
The principle that the total electric field at a point is the vector sum of the electric fields of all the charges is called the ______ principle.
Match the following definitions with the correct term:
Match the following definitions with the correct term:
Which of the following statements is true regarding conductors and insulators?
Which of the following statements is true regarding conductors and insulators?
Charging by induction requires physical contact between the charged object and the object being charged.
Charging by induction requires physical contact between the charged object and the object being charged.
Define the term grounding in the context of charging objects.
Define the term grounding in the context of charging objects.
The process of charging an object by bringing a charged object nearby and connecting a grounding wire is known as charging by ______.
The process of charging an object by bringing a charged object nearby and connecting a grounding wire is known as charging by ______.
Which of the following is an example of electrical conductors?
Which of the following is an example of electrical conductors?
The magnitude of the electric force increases as the distance squared increase between the two charges.
The magnitude of the electric force increases as the distance squared increase between the two charges.
State Coulomb's Law.
State Coulomb's Law.
The constant k in Coulomb's law is known as the ______ constant.
The constant k in Coulomb's law is known as the ______ constant.
Match the descriptions with the appropriate term:
Match the descriptions with the appropriate term:
What is the permittivity of free space?
What is the permittivity of free space?
The electric force is always attractive.
The electric force is always attractive.
State the relationship between the charge of a hydrogen atom's proton and electron.
State the relationship between the charge of a hydrogen atom's proton and electron.
Robert Millikan discovered that electric charge is ______.
Robert Millikan discovered that electric charge is ______.
In a region of space, there is more electrical field when...
In a region of space, there is more electrical field when...
It is possible for two field lines to cross each other.
It is possible for two field lines to cross each other.
An atom has 2 electrons, what results?
An atom has 2 electrons, what results?
The density of the lines are ______ where the electrical field is stronger.
The density of the lines are ______ where the electrical field is stronger.
Is the charge equal between molecules?
Is the charge equal between molecules?
True or False: if the charge has the same sign the force is attractive, otherwise is on the other direction.
True or False: if the charge has the same sign the force is attractive, otherwise is on the other direction.
Electrical field lines show the path that a charged molecule may take.
Electrical field lines show the path that a charged molecule may take.
A charge of +3 uC is put near a external field of 4x10^6 N/C being push to the right, is that situation afected if the charge is replaces wiht a -3uC?
A charge of +3 uC is put near a external field of 4x10^6 N/C being push to the right, is that situation afected if the charge is replaces wiht a -3uC?
Flashcards
Electric Field (E)
Electric Field (E)
A vector with SI units of newtons per coulomb (N/C) which represents the force a positive test charge experiences.
F = qE
F = qE
An equation that expresses the electric force (F) on an arbitrary charge (q) in an electric field (E).
Point Charge
Point Charge
A charged particle of zero size, used to simplify analysis of electric forces. Electrical behavior of electrons and protons are well described by this model
Coulomb's Law
Coulomb's Law
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Coulomb Constant (k)
Coulomb Constant (k)
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Permittivity of Free Space (ε₀)
Permittivity of Free Space (ε₀)
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Charge Quantization
Charge Quantization
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Electrical Conductor
Electrical Conductor
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Electrical Insulator
Electrical Insulator
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Charging by Induction
Charging by Induction
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Superposition Principle
Superposition Principle
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Electric Dipole
Electric Dipole
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Continuous Charge Distribution
Continuous Charge Distribution
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Volume Charge Density (ρ)
Volume Charge Density (ρ)
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Surface Charge Density (σ)
Surface Charge Density (σ)
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Linear Charge Density (λ)
Linear Charge Density (λ)
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Electric Field Lines
Electric Field Lines
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Motion in a Uniform Electric Field
Motion in a Uniform Electric Field
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Study Notes
- The vector E has the SI units of newtons per coulomb (N/C).
- The direction of E is the direction of the force a positive test charge experiences when placed in the field.
- E is produced by a charge or charge distribution separate from the test charge.
- The existence of an electric field is a property of its source; the presence of the test charge is not necessary for the field to exist.
- The test charge serves as a detector of the electric field.
- A test charge at a point experiences an electric force if an electric field exists at that point.
- If an arbitrary charge q is placed in an electric field E, it experiences an electric force given by F=qE.
- If q is positive, the force is in the same direction as the field.
- If q is negative, the force and the field are in opposite directions.
- This equation is the mathematical representation of the electric version of the particle in a field analysis model.
- Once the magnitude and direction of the electric field are known at some point, the electric force exerted on any charged particle placed at that point can be calculated from F=qE.
- To determine the direction of an electric field, consider a point charge q as a source charge.
- This charge creates an electric field at all points in space surrounding it.
- A test charge q₀ is placed at point P, a distance r from the source charge.
- The force exerted by q on the test charge is F=(ke q q₀/r²)r̂, where r̂ is a unit vector directed from q toward q₀.
- Because the electric field at P is defined by E = F/q₀, the electric field at P created by q is E = (ke q/r²)r̂.
- If the source charge q is positive, the source charge sets up an electric field at P directed away from q.
- If q is negative, the force on the test charge is toward the source charge, and the electric field at P is directed toward the source charge.
- To calculate the electric field at a point P due to a small number of point charges, calculate the electric field vectors at P individually using E = (ke q/r²)r̂ and then add them vectorially.
- At any point P, the total electric field due to a group of source charges equals the vector sum of the electric fields of all the charges E = Σ ke qi/r², i=1 to n.
- This superposition principle applied to fields follows directly from the vector addition of electric forces.
- An electric dipole is defined as a positive charge q and a negative charge -q separated by a distance 2a.
- The electric dipole is a good model for many molecules, such as hydrochloric acid (HCl).
- Neutral atoms and molecules behave as dipoles when placed in an external electric field.
- Many molecules, such as HCl, are permanent dipoles.
- An object with charge establishes an electric field E throughout space.
- Imagine a particle with charge q is placed in that field, it interacts with the electric field, and experiences an electric force given by F=qE.
- An electric dipole contains a positive charge and a negative charge separated by a distance.
- The electric dipole is a good model of many molecules such as hydrochloric acid.
- Neutral atoms and molecules behave as dipoles when placed in an external electric field.
- To calculate the electric field due to a small number of charges, first calculate each electric field vector, then add all the vectors.
- The vector E has the SI units of newtons per coulomb (N/C).
- The direction of E is the direction of the force a positive test charge experiences when placed in the field .
- Equation 23.10 is useful for calculating the electric field due to a small number of charges.
- In many cases, we have a continuous distribution of charge rather than a collection of discrete charges.
- The charge in these situations can be described as continuously distributed along some line, over some surface, or throughout some volume.
- To set up the process for evaluating the electric field created by a continuous charge distribution, let's first divide the charge distribution into small elements, each of which contains a small charge Δq.
- Next, use Equation E = (ke q/r²)r̂ to calculate the electric field due to one of these elements at a point P.
- Finally, evaluate the total electric field at P due to the charge distribution by summing the contributions of all the charge elements.
- The electric field at P due to one charge element carrying charge Δq is ΔE = ke (Δ q/r²)r̂.
- The integration in Equation E = k∫ (dq/r²)r̂ is a vector operation and must be treated appropriately.
- Volume charge density is defined as ρ = Q/V, where ρ has units of coulombs per cubic meter (C/m³).
- Surface charge density is defined as σ= Q/A, where σ has units of coulombs per square meter (C/m²).
- Linear charge density is defined as λ = Q/l, where λ has units of coulombs per meter (C/m).
- If the charge is nonuniformly distributed over a volume, surface, or line, the amounts of charge dq in a small volume, surface, or length element are dq = ρ dV, dq = σ dA and dq = λ dl.
- Electrical conductors are materials in which some of the electrons are free electrons that are not bound to atoms and can move relatively freely through the material.
- Electrical insulators are materials in which all electrons are bound to atoms and cannot move freely through the material.
- Materials such as glass, rubber, and dry wood fall into the category of electrical insulators.
- When such materials are charged by rubbing, only the area rubbed becomes charged and the charged particles are unable to move to other regions of the material.
- In contrast, materials such as copper, aluminum, and silver are good electrical conductors.
- When such materials are charged in some small region, the charge readily distributes itself over the entire surface of the material.
- Semiconductors are a third class of materials, and their electrical properties are somewhere between those of insulators and those of conductors.
- Charges of the same sign repel one another and charges with opposite signs attract one another.
- A metal atom contains one or more outer electrons, which are weakly bound to the nucleus.
- When many atoms combine to form a metal, the free electrons are these outer electrons, which are not bound to any one atom and move about the metal in a manner similar to that of gas molecules moving in a container.
- We use the term point charge to refer to a charged particle of zero size, so we can generalize the properties of the electric force between two point charges
- The magnitude of the electric force between two point charges is given by Coulomb's law, F=k (|q₁||q₂|/r²).
- The constant k is called the Coulomb constant and is k = 8.987 6 × 10º N. m²/C², the SI unit of charge is the coulomb (C), which depends on the choice of units.
- The constant k can also be written in the form k = 1/(4πε₀), where the constant ε₀ is known as the permittivity of free space and has the value ε₀ = 8.854 2 × 10⁻¹² C²/N. m².
- The smallest unit of free charge e known in nature, the charge on an electron (-e) or a proton (+e), has a magnitude e = 1.602 18 × 10⁻¹⁹ C.
- Therefore, 1 C of charge is approximately equal to the charge of 6.24 × 10¹⁸ electrons or protons.
- When calculating the electric force between two charges remembers that force is a vector quantity and must be treated accordingly.
- Coulomb's law expressed in vector form for the electric force exerted by a charge q₁ on a second charge q₂, written F₁₂, is F₁₂ = k (q₁ q₂/r² )r̂₁₂ (23.6) where r̂₁₂ is a unit vector directed from q₁ toward q₂
- if q₁ and q₂ are of the same sign as in Figure 23.6a, the product q₁q₂ is positive and the electric force on one particle is directed away from the other particle.
- Electric field lines provide a method of visualizing the field in three dimensions.
- They have a direction, as given by the force that a positive charge would experience when placed within the field.
- They are related to the electric field in the following manner:
- The electric field vector E is tangent to the electric field line at each point.
- The number of lines per unit area through a surface perpendicular to the lines is proportional to the magnitude of the electric field in that region.
- Some rules that can be followed when drawing electric field lines are:
- The lines must begin on a positive charge and terminate on a negative charge.
- The number of lines drawn leaving a positive charge or approaching a negative charge is proportional to the magnitude of the charge
- In addition a "Coulomb Mist"
- If the amount of charge transfer between objects is too great it will "leak" to the Earth.
- The total charge in an isolated system remains constant.
- Electric charge always occurs as integral multiples of a fundamental amount of charge e (q=±Ne).
- Conductors are materials in which electrons can easily move.
- Electric forces and fields may seem abstract to you. Once Fs is evaluated, however, it causes a particle to move according to our well-established models of forces and motion from Chapters 2 through 6.
- Given an electric field and a charge q the net force exerted can be calculated as F=qE.
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