Physics Flashcards: Apply Coulombs Law

What this deck covers

This deck focuses on Apply Coulombs Law, giving you a quick way to review the definitions, rules, and examples that matter most for Physics.

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Work through these flashcards in short sessions. Try to answer each prompt before flipping the card, then revisit any cards you miss until the explanation feels automatic.

Flashcard 1: Find $q_2$ if $F=0.90\ \text{N}$, $q_1=+1\times 10^{-6}\ \text{C}$, and $r=0.10\ \text{m}$.

Answer: $|q_2|\approx 1.0\times 10^{-6}\ \text{C}$. $|q_2| = \frac{Fr^2}{k|q_1|} = \frac{0.90 \times 0.01}{8.99\times10^9 \times 10^{-6}} \approx 1.0\times10^{-6}\ \text{C}$

Flashcard 2: What is the direction of the force between two charges with the same sign?

Answer: Repulsive; along the line joining the charges. Like charges repel each other directly along their connecting line.

Flashcard 3: State the inverse-square relationship between force and separation distance in Coulomb's law.

Answer: $F \propto \frac{1}{r^2}$. Force decreases with the square of the distance between charges.

Flashcard 4: Calculate $F$ for $q_1=+1\times 10^{-6}\ \text{C}$, $q_2=-1\times 10^{-6}\ \text{C}$, $r=0.10\ \text{m}$.

Answer: $F\approx 0.90\ \text{N}$ (attractive). $F = 8.99\times10^9 \times \frac{1\times10^{-12}}{0.01} \approx 0.90\ \text{N}$, opposite signs attract.

Flashcard 5: Calculate $F_{\text{net}}$ on $q_2$ if $q_1=+1\times10^{-6}\ \text{C}$ at $0.10\ \text{m}$ left and $q_3=+1\times10^{-6}\ \text{C}$ at $0.10\ \text{m}$ right.

Answer: $F_{\text{net}}=0\ \text{N}$. Equal charges at equal distances create equal but opposite forces that cancel.

Flashcard 6: Find the force ratio $\frac{F_2}{F_1}$ if the distance changes from $r_1$ to $r_2=3r_1$.

Answer: $\frac{F_2}{F_1}=\frac{1}{9}$. Since $F \propto 1/r^2$, tripling $r$ reduces force by factor of 9.

Flashcard 7: Find $r$ if $q_1=q_2=+1\times 10^{-6}\ \text{C}$ and the force magnitude is $F=1.0\ \text{N}$.

Answer: $r\approx 0.095\ \text{m}$. $r = \sqrt{\frac{k|q_1q_2|}{F}} = \sqrt{\frac{8.99\times10^{-3}}{1.0}} \approx 0.095\ \text{m}$

Flashcard 8: Identify whether the force is attractive or repulsive for $q_1=+2\ \mu\text{C}$ and $q_2=-5\ \mu\text{C}$.

Answer: Attractive. Opposite signs ($+$ and $-$) mean attractive force.

Flashcard 9: What is the direction of the Coulomb force on each charge relative to the line joining them?

Answer: Along the line connecting the charges. Electric forces act along the line between charges.

Flashcard 10: What is the SI value of Coulomb's constant $k$ used in Coulomb's law?

Answer: $k = 8.99\times 10^9\ \text{N}\cdot\text{m}^2/\text{C}^2$. This constant relates charge, distance, and force in SI units.

Flashcard 11: What is the net force magnitude if two forces of $5\ \text{N}$ and $3\ \text{N}$ act on a charge in opposite directions?

Answer: $2\ \text{N}$. Forces in opposite directions subtract: $5 - 3 = 2$ N.

Flashcard 12: Identify the vector direction of the force on $q_1$ due to $q_2$ in Coulomb's law problems.

Answer: Along the line from $q_1$ to $q_2$ (toward or away). Force acts along the line connecting the charges.

Flashcard 13: What is the net force magnitude if two forces of $3\ \text{N}$ and $5\ \text{N}$ act on a charge in the same direction?

Answer: $8\ \text{N}$. Forces in same direction add: $3 + 5 = 8$ N.

Flashcard 14: Calculate $F$ for $q_1=+4\times 10^{-6}\ \text{C}$, $q_2=+2\times 10^{-6}\ \text{C}$, $r=0.20\ \text{m}$.

Answer: $F\approx 1.8\ \text{N}$. $F = 8.99\times10^9 \times \frac{8\times10^{-12}}{0.04} \approx 1.8\ \text{N}$

Flashcard 15: What is the sign of the force between like charges (both $+$ or both $-$)?

Answer: Repulsive. Like charges repel each other.

Flashcard 16: What happens to $F$ if both charges change from $(q_1,q_2)$ to $(2q_1,3q_2)$ with $r$ unchanged?

Answer: $F\to 6F$. Force scales with product of charges: $2 \times 3 = 6$.

Flashcard 17: State the formula for the magnitude of the electric force between two point charges.

Answer: $F = k\frac{|q_1 q_2|}{r^2}$. Force is proportional to charge product and inversely proportional to distance squared.

Flashcard 18: What is the direction of the force between two charges with opposite signs?

Answer: Attractive; along the line joining the charges. Opposite charges attract each other directly along their connecting line.

Flashcard 19: What happens to $F$ if the separation distance changes from $r$ to $2r$ (charges unchanged)?

Answer: $F\to \frac{F}{4}$. Doubling distance reduces force by factor of $2^2 = 4$.

Flashcard 20: What is the value of Coulomb's constant $k$ in $\text{N}\cdot\text{m}^2/\text{C}^2$?

Answer: $k = 8.99\times 10^9\ \text{N}\cdot\text{m}^2/\text{C}^2$. This fundamental constant relates charge, distance, and force in SI units.

Flashcard 21: For three collinear charges, what principle tells you the net force on one charge is the vector sum of pairwise forces?

Answer: Superposition: $\vec{F}_{\text{net}}=\sum \vec{F}_i$. Vector sum of individual forces gives the net force on a charge.

Flashcard 22: What is the net force magnitude on $q_3$ if two equal forces of $5\ \text{N}$ act on it in opposite directions?

Answer: $0\ \text{N}$. Equal forces in opposite directions cancel out.

Flashcard 23: State Newton's third law relationship for the forces two charges exert on each other.

Answer: $\vec{F}_{12}=-\vec{F}_{21}$. Forces form an action-reaction pair with equal magnitude, opposite direction.

Flashcard 24: What happens to $F$ if the separation distance changes from $r$ to $2r$?

Answer: $F\rightarrow\frac{F}{4}$. Force decreases by factor of $r^2$, so doubling $r$ gives $F/4$.

Flashcard 25: Identify the SI unit of electric charge used in Coulomb's law calculations.

Answer: $\text{coulomb (C)}$. The standard unit for measuring electric charge in the SI system.

Flashcard 26: What is the sign of the force between opposite charges (one $+$ and one $-$)?

Answer: Attractive. Opposite charges attract each other.

Flashcard 27: State the formula for the magnitude of the electrostatic force between two point charges.

Answer: $F = k\frac{|q_1 q_2|}{r^2}$. Force is proportional to charge product and inversely proportional to distance squared.

Flashcard 28: Identify the SI unit of electric charge used in Coulomb's law.

Answer: $\text{coulomb (C)}$. Named after Charles-Augustin de Coulomb who discovered the law.

Flashcard 29: What happens to $F$ if the separation distance changes from $r$ to $\frac{r}{3}$ (charges unchanged)?

Answer: $F\to 9F$. Reducing distance by 3 increases force by factor of $3^2 = 9$.

Flashcard 30: Find the force ratio $\frac{F_2}{F_1}$ if $q_1$ is tripled and $q_2$ is halved while $r$ stays constant.

Answer: $\frac{F_2}{F_1}=\frac{3}{2}$. Force ratio equals charge product ratio: $(3)(1/2) = 3/2$.

Flashcard 31: What happens to $F$ if the separation distance changes from $r$ to $\frac{r}{3}$?

Answer: $F\rightarrow 9F$. Force increases by factor of $r^2$, so $r/3$ gives $9F$.

Flashcard 32: Identify the SI unit of electric force in Coulomb's law problems.

Answer: $\text{newton (N)}$. Force is measured in newtons in the SI system.

Flashcard 33: What happens to $F$ if $q_1$ is doubled while $q_2$ and $r$ stay the same?

Answer: $F\rightarrow 2F$. Force is directly proportional to each charge.

Flashcard 34: State Newton's third-law relationship for the forces between two point charges.

Answer: $\vec{F}_{12} = -\vec{F}_{21}$. Forces form an action-reaction pair with equal magnitude, opposite direction.