MCAT Chemical and Physical Foundations of Biological Systems Flashcards: 4c Electrostatics Electric Fields

What this deck covers

This deck focuses on 4c Electrostatics Electric Fields, giving you a quick way to review the definitions, rules, and examples that matter most for MCAT Chemical and Physical Foundations of Biological Systems.

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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: What is the SI unit of electric potential $V$?

Answer: Volt (V) = $\text{J/C}$. The volt equals one joule of energy per coulomb of charge.

Flashcard 2: State the superposition principle for the net electric field from multiple charges.

Answer: $\vec{E}_{\text{net}} = \sum_i \vec{E}_i$. Electric fields obey vector addition, allowing the total field to be the sum of individual contributions.

Flashcard 3: Find the net electric field at the midpoint between charges $+Q$ and $-Q$ separated by $2d$ (direction only).

Answer: Toward the $-Q$ charge (from $+Q$ to $-Q$). Fields from opposite charges at the midpoint add constructively, pointing towards the negative charge.

Flashcard 4: State the formula for the electric field magnitude due to a point charge $Q$ a distance $r$ away.

Answer: $E = k\frac{|Q|}{r^2}$. The expression comes from dividing the Coulomb force on a test charge by its magnitude.

Flashcard 5: State the relationship between work done by the electric field and potential difference for charge $q$.

Answer: $W_{\text{field}} = -q\Delta V$. For conservative fields, work by the field equals the negative change in potential energy.

Flashcard 6: Identify the relationship between electric field magnitude and potential gradient in 1D along $x$.

Answer: $E_x = -\frac{dV}{dx}$. The electric field component is the negative rate of change of potential with position.

Flashcard 7: State the value of the elementary charge magnitude, $e$, in coulombs.

Answer: $e = 1.60 \times 10^{-19}\ \text{C}$. This magnitude represents the fundamental unit of charge carried by a proton or electron.

Flashcard 8: Identify the sign of $\Delta U$ when a positive charge moves in the direction of $\vec{E}$.

Answer: $\Delta U < 0$. Moving along the field decreases potential for positive charges, reducing potential energy.

Flashcard 9: State the definition of electric field in terms of force on a test charge.

Answer: $\vec{E} = \frac{\vec{F}}{q}$. The electric field is defined as the electrostatic force per unit positive test charge at a point.

Flashcard 10: State the formula for electric potential energy of two point charges separated by $r$ (zero at infinity).

Answer: $U = k\frac{q_1 q_2}{r}$. This represents the work to assemble the charges from infinite separation, positive for like charges.

Flashcard 11: What is the relationship between $k$, $\varepsilon_0$, and $\pi$?

Answer: $k = \frac{1}{4\pi\varepsilon_0}$. Coulomb's constant relates to the vacuum permittivity through this expression in electrostatics.

Flashcard 12: State the definition of electric potential difference in terms of potential energy change and charge.

Answer: $\Delta V = \frac{\Delta U}{q}$. Potential difference measures the change in potential energy per unit charge moved between points.

Flashcard 13: State the electric potential (voltage) due to a point charge $Q$ at distance $r$ (zero at infinity).

Answer: $V = k\frac{Q}{r}$. The potential is the work per unit charge to bring a test charge from infinity to that point.

Flashcard 14: Which direction does $\vec{E}$ point around an isolated positive point charge?

Answer: Radially outward from the charge. The field direction indicates the force on a positive test charge, repelling from a positive source.

Flashcard 15: What is the approximate value of Coulomb's constant, $k$, in vacuum?

Answer: $k \approx 9.0 \times 10^9\ \text{N·m}^2/\text{C}^2$. This value is derived from fundamental constants and used in Coulomb's law for vacuum.

Flashcard 16: Which direction does $\vec{E}$ point around an isolated negative point charge?

Answer: Radially inward toward the charge. The field points in the direction a positive test charge would be forced, attracting to a negative source.

Flashcard 17: State the magnitude of the uniform electric field between parallel plates with potential difference $\Delta V$ and spacing $d$.

Answer: $E = \frac{\Delta V}{d}$. In uniform fields, the field strength equals the potential gradient across the plate separation.

Flashcard 18: Identify the rule relating electric field lines to equipotential surfaces.

Answer: Field lines intersect equipotentials at $90^\circ$. The field direction is perpendicular to surfaces of constant potential, following the gradient.

Flashcard 19: State Coulomb's law for the magnitude of the electrostatic force between two point charges.

Answer: $F = k\frac{|q_1 q_2|}{r^2}$. The law states that the force is proportional to the product of charges and inversely proportional to the square of the distance.

Flashcard 20: How does the electrostatic force magnitude change if the separation doubles: $r \to 2r$?

Answer: $F \to \frac{F}{4}$. Coulomb's law's inverse square dependence on distance quarters the force when distance doubles.

Flashcard 21: What is the direction of the electric field between parallel plates: from $+$ plate to $-$ plate or the reverse?

Answer: From the $+$ plate toward the $-$ plate. The field points from higher to lower potential, consistent with force on positive charges.

Flashcard 22: Find the net electric field at the midpoint between equal charges $+Q$ and $+Q$ separated by $2d$.

Answer: $E_{\text{net}} = 0$. At the midpoint, fields from identical charges are equal in magnitude but opposite in direction, canceling out.

Flashcard 23: How does the electric field magnitude from a point charge change if distance triples: $r \to 3r$?

Answer: $E \to \frac{E}{9}$. The inverse square law reduces the field to one-ninth when distance increases by a factor of three.

Flashcard 24: What is the SI unit of electric charge?

Answer: Coulomb (C). The coulomb quantifies electric charge in the SI system as the charge transported by a constant current of one ampere in one second.

Flashcard 25: What is the SI unit of electric field magnitude $E$?

Answer: $\text{N/C}$ (equivalently $\text{V/m}$). The unit derives from force per unit charge or equivalently potential difference per unit distance.