Model Electric and Magnetic Fields - Physics
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What is the direction of the electric field around a positive point charge?
What is the direction of the electric field around a positive point charge?
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Radially outward from the charge. Field lines point away from positive charges.
Radially outward from the charge. Field lines point away from positive charges.
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What is the formula for the electric force magnitude between two point charges?
What is the formula for the electric force magnitude between two point charges?
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$F = k\frac{|q_1 q_2|}{r^2}$. Coulomb's law: force is proportional to charge product and inversely to distance squared.
$F = k\frac{|q_1 q_2|}{r^2}$. Coulomb's law: force is proportional to charge product and inversely to distance squared.
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What is the value of Coulomb's constant $k$ in vacuum (to $3$ significant figures)?
What is the value of Coulomb's constant $k$ in vacuum (to $3$ significant figures)?
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$k = 8.99\times 10^9\ \text{N}\cdot\text{m}^2/\text{C}^2$. This constant relates charge, distance, and force in Coulomb's law.
$k = 8.99\times 10^9\ \text{N}\cdot\text{m}^2/\text{C}^2$. This constant relates charge, distance, and force in Coulomb's law.
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What is the definition of electric field magnitude $E$ in terms of force on a test charge?
What is the definition of electric field magnitude $E$ in terms of force on a test charge?
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$E = \frac{F}{q}$. Electric field is force per unit charge on a test charge.
$E = \frac{F}{q}$. Electric field is force per unit charge on a test charge.
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What is the electric field magnitude produced by a point charge $Q$ at distance $r$?
What is the electric field magnitude produced by a point charge $Q$ at distance $r$?
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$E = k\frac{|Q|}{r^2}$. Combines Coulomb's law with $E = F/q$ for a point charge field.
$E = k\frac{|Q|}{r^2}$. Combines Coulomb's law with $E = F/q$ for a point charge field.
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What is the direction of the electric field around a negative point charge?
What is the direction of the electric field around a negative point charge?
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Radially inward toward the charge. Field lines point toward negative charges.
Radially inward toward the charge. Field lines point toward negative charges.
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What is the formula for electric potential energy of two point charges separated by distance $r$?
What is the formula for electric potential energy of two point charges separated by distance $r$?
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$U = k\frac{q_1 q_2}{r}$. No $r^2$ in denominator; energy, not force.
$U = k\frac{q_1 q_2}{r}$. No $r^2$ in denominator; energy, not force.
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What is the definition of electric potential difference (voltage) in terms of work and charge?
What is the definition of electric potential difference (voltage) in terms of work and charge?
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$\Delta V = \frac{\Delta U}{q}$. Voltage is work per unit charge moved between points.
$\Delta V = \frac{\Delta U}{q}$. Voltage is work per unit charge moved between points.
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What is the relationship between uniform electric field and potential difference over distance $d$?
What is the relationship between uniform electric field and potential difference over distance $d$?
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$E = \frac{\Delta V}{d}$. In uniform fields, voltage drop is proportional to distance.
$E = \frac{\Delta V}{d}$. In uniform fields, voltage drop is proportional to distance.
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What is the equation for the electric force on a charge $q$ placed in an electric field $E$?
What is the equation for the electric force on a charge $q$ placed in an electric field $E$?
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$F = qE$. Force equals charge times field strength.
$F = qE$. Force equals charge times field strength.
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What is the definition of magnetic force on a moving charge $q$ with speed $v$ in field $B$?
What is the definition of magnetic force on a moving charge $q$ with speed $v$ in field $B$?
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$F = qvB\sin(\theta)$. Lorentz force depends on velocity, field, and angle between them.
$F = qvB\sin(\theta)$. Lorentz force depends on velocity, field, and angle between them.
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What is the direction rule for magnetic force on a positive charge moving in a magnetic field?
What is the direction rule for magnetic force on a positive charge moving in a magnetic field?
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Right-hand rule for $\vec{F} = q\vec{v}\times\vec{B}$. Fingers follow $\vec{v}$, curl to $\vec{B}$, thumb shows $\vec{F}$.
Right-hand rule for $\vec{F} = q\vec{v}\times\vec{B}$. Fingers follow $\vec{v}$, curl to $\vec{B}$, thumb shows $\vec{F}$.
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What is the magnetic force magnitude on a straight wire of length $L$ carrying current $I$ in field $B$?
What is the magnetic force magnitude on a straight wire of length $L$ carrying current $I$ in field $B$?
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$F = ILB\sin(\theta)$. Current $I$ is moving charge; replaces $qv$ in force formula.
$F = ILB\sin(\theta)$. Current $I$ is moving charge; replaces $qv$ in force formula.
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What is the magnetic field magnitude at distance $r$ from a long straight wire carrying current $I$?
What is the magnetic field magnitude at distance $r$ from a long straight wire carrying current $I$?
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$B = \frac{\mu_0 I}{2\pi r}$. Ampère's law result for infinite straight wire.
$B = \frac{\mu_0 I}{2\pi r}$. Ampère's law result for infinite straight wire.
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What is the value of the permeability of free space $\mu_0$ (exact in SI form)?
What is the value of the permeability of free space $\mu_0$ (exact in SI form)?
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$\mu_0 = 4\pi\times 10^{-7}\ \text{T}\cdot\text{m}/\text{A}$. Fundamental constant relating magnetic field to current.
$\mu_0 = 4\pi\times 10^{-7}\ \text{T}\cdot\text{m}/\text{A}$. Fundamental constant relating magnetic field to current.
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What is the direction of magnetic field lines around a straight current-carrying wire?
What is the direction of magnetic field lines around a straight current-carrying wire?
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Concentric circles given by the right-hand grip rule. Thumb along current, fingers curl in field direction.
Concentric circles given by the right-hand grip rule. Thumb along current, fingers curl in field direction.
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Identify the net electric field direction at the midpoint between equal positive charges $+Q$ and $+Q$.
Identify the net electric field direction at the midpoint between equal positive charges $+Q$ and $+Q$.
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Zero; the fields cancel at the midpoint. Equal charges create equal opposing fields at midpoint.
Zero; the fields cancel at the midpoint. Equal charges create equal opposing fields at midpoint.
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Identify the net electric field direction at the midpoint between charges $+Q$ (left) and $-Q$ (right).
Identify the net electric field direction at the midpoint between charges $+Q$ (left) and $-Q$ (right).
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To the right, toward $-Q$. Both charges' fields point right at midpoint, adding up.
To the right, toward $-Q$. Both charges' fields point right at midpoint, adding up.
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Which option gives the direction of force on an electron moving right in a magnetic field into the page?
Which option gives the direction of force on an electron moving right in a magnetic field into the page?
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Downward. Right-hand rule: $\vec{v}$ right, $\vec{B}$ in gives $\vec{F}$ up; electron reverses to down.
Downward. Right-hand rule: $\vec{v}$ right, $\vec{B}$ in gives $\vec{F}$ up; electron reverses to down.
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What is the magnetic force on a charge moving parallel to a magnetic field (any nonzero $v$)?
What is the magnetic force on a charge moving parallel to a magnetic field (any nonzero $v$)?
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$F = 0$. $\sin(0°) = 0$ when velocity is parallel to field.
$F = 0$. $\sin(0°) = 0$ when velocity is parallel to field.
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What is the relationship between electric potential difference and potential energy change?
What is the relationship between electric potential difference and potential energy change?
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$\Delta V = \frac{\Delta U}{q}$. Potential is energy per unit charge.
$\Delta V = \frac{\Delta U}{q}$. Potential is energy per unit charge.
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What is the electric potential energy of two point charges separated by distance $r$?
What is the electric potential energy of two point charges separated by distance $r$?
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$U = k\frac{q_1 q_2}{r}$. Energy is proportional to charge product, inversely to separation.
$U = k\frac{q_1 q_2}{r}$. Energy is proportional to charge product, inversely to separation.
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What is the definition of electric field at a point in terms of force and test charge?
What is the definition of electric field at a point in terms of force and test charge?
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$\vec{E} = \frac{\vec{F}}{q}$. Field is force per unit positive test charge.
$\vec{E} = \frac{\vec{F}}{q}$. Field is force per unit positive test charge.
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What is the direction of the electric force between two charges with the same sign?
What is the direction of the electric force between two charges with the same sign?
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Repulsive; each force points away from the other charge. Like charges repel according to Coulomb's law.
Repulsive; each force points away from the other charge. Like charges repel according to Coulomb's law.
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What is the electric force magnitude between two point charges separated by distance $r$?
What is the electric force magnitude between two point charges separated by distance $r$?
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$F = k\frac{|q_1 q_2|}{r^2}$. Coulomb's law: force is proportional to charge product and inversely to distance squared.
$F = k\frac{|q_1 q_2|}{r^2}$. Coulomb's law: force is proportional to charge product and inversely to distance squared.
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What is the direction of electric field lines relative to equipotential lines?
What is the direction of electric field lines relative to equipotential lines?
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Perpendicular to equipotential lines. Field points from high to low potential, perpendicular to constant potential surfaces.
Perpendicular to equipotential lines. Field points from high to low potential, perpendicular to constant potential surfaces.
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Which option gives the direction of magnetic force on a positive charge: $\vec{F} = q\vec{v}\times\vec{B}$?
Which option gives the direction of magnetic force on a positive charge: $\vec{F} = q\vec{v}\times\vec{B}$?
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Right-hand rule for $\vec{v}\times\vec{B}$; reverse for negative $q$. Cross product gives force direction; thumb points along $\vec{F}$ for positive charge.
Right-hand rule for $\vec{v}\times\vec{B}$; reverse for negative $q$. Cross product gives force direction; thumb points along $\vec{F}$ for positive charge.
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What is the magnetic force magnitude on a straight wire of length $L$ carrying current $I$ in field $B$ at angle $\theta$?
What is the magnetic force magnitude on a straight wire of length $L$ carrying current $I$ in field $B$ at angle $\theta$?
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$F = ILB\sin\theta$. Current is moving charge; force maximized when wire perpendicular to field.
$F = ILB\sin\theta$. Current is moving charge; force maximized when wire perpendicular to field.
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What is the magnetic field magnitude at the center of a single circular loop of radius $R$ carrying current $I$?
What is the magnetic field magnitude at the center of a single circular loop of radius $R$ carrying current $I$?
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$B = \frac{\mu_0 I}{2R}$. Biot-Savart law result for loop center.
$B = \frac{\mu_0 I}{2R}$. Biot-Savart law result for loop center.
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What is the magnetic flux through a flat area $A$ in uniform field $B$ at angle $\theta$ to the area normal?
What is the magnetic flux through a flat area $A$ in uniform field $B$ at angle $\theta$ to the area normal?
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$\Phi_B = BA\cos\theta$. Flux is field component perpendicular to surface times area.
$\Phi_B = BA\cos\theta$. Flux is field component perpendicular to surface times area.
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