Electric Potential Energy

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AP Physics C: Electricity and Magnetism › Electric Potential Energy

Questions 1 - 8
1

Based on the scenario, calculate the change in electric potential energy for a $+1.5,\mu\text{C}$ charge moved through a battery from 0 V to 12 V.

$+1.8\times10^{-5},\text{J}$

$+18,\text{J}$

$-1.8\times10^{-5},\text{J}$

$+12,\text{J}$

Explanation

This question tests AP Physics C skills in understanding electric potential energy within electric fields. Electric potential energy (U) is the energy a charge has due to its position in an electric field, calculated by U = qV. In this scenario, the positive charge moved through a battery from 0 V to 12 V experiences a potential difference of ΔV = 12 - 0 = 12 V. The correct answer, A, is derived by applying ΔU = qΔV = (1.5×10⁻⁶ C)(12 V) = 1.8×10⁻⁵ J. A common distractor, B, arises from incorrect unit conversion, treating microCoulombs as Coulombs. To assist students, emphasize careful unit conversion (1 μC = 10⁻⁶ C) and practice dimensional analysis to ensure energy units (Joules) result from charge (Coulombs) times potential (Volts).

2

In the context of the electric field, calculate the change in electric potential energy for a $-1.0,\mu\text{C}$ charge moving 0.40 m along a uniform $300,\text{V/m}$ field.

$+1.2\times10^{-4},\text{J}$

$-1.2\times10^{-4},\text{J}$

$+1.2\times10^{-5},\text{J}$

$-120,\text{V}$

Explanation

This question tests AP Physics C skills in understanding electric potential energy within electric fields. Electric potential energy (U) is the energy a charge has due to its position in an electric field, calculated by U = qV. In this scenario, the negative charge moving 0.40 m along a 300 V/m field experiences a potential difference of ΔV = -Ed = -300 × 0.40 = -120 V. The correct answer, B, is derived by applying ΔU = qΔV = (-1.0×10⁻⁶ C)(-120 V) = 1.2×10⁻⁴ J. A common distractor, A, arises from forgetting that negative charges gain energy when moving along field lines (toward lower potential). To assist students, emphasize that negative charges behave oppositely to positive charges in terms of energy changes, gaining energy when moving in the field direction.

3

Based on the scenario, calculate the change in electric potential energy for a $+4.0,\mu\text{C}$ charge moving from 120 V to 60 V in a circuit.

$-2.4\times10^{-6},\text{J}$

$-2.4\times10^{-4},\text{J}$

$+2.4\times10^{-4},\text{J}$

$-60,\text{V}$

Explanation

This question tests AP Physics C skills in understanding electric potential energy within electric fields. Electric potential energy (U) is the energy a charge has due to its position in an electric field, calculated by U = qV. In this scenario, the positive charge moving from 120 V to 60 V experiences a potential difference of ΔV = 60 - 120 = -60 V. The correct answer, A, is derived by applying ΔU = qΔV = (4.0×10⁻⁶ C)(-60 V) = -2.4×10⁻⁴ J. A common distractor, B, arises from incorrectly assigning the sign, thinking that moving to lower potential should increase energy. To assist students, emphasize that positive charges naturally move toward lower potentials, losing potential energy in the process, similar to objects falling in gravitational fields.

4

In the context of the electric field, calculate the change in electric potential energy for a $-2.0,\mu\text{C}$ charge moving from 5 V to 25 V.

$-4.0\times10^{-5},\text{J}$

$+4.0\times10^{-5},\text{J}$

$-40,\text{J}$

$+20,\text{V}$

Explanation

This question tests AP Physics C skills in understanding electric potential energy within electric fields. Electric potential energy (U) is the energy a charge has due to its position in an electric field, calculated by U = qV. In this scenario, the negative charge moving from 5 V to 25 V experiences a potential difference of ΔV = 25 - 5 = 20 V. The correct answer, B, is derived by applying ΔU = qΔV = (-2.0×10⁻⁶ C)(20 V) = -4.0×10⁻⁵ J. A common distractor, A, arises from forgetting that negative charges lose potential energy when moving to higher potentials. To assist students, emphasize that the sign of ΔU depends on both the charge sign and the direction of potential change, and practice interpreting physical meaning of energy changes.

5

In the context of the electric field, calculate the change in electric potential energy for a $+2.5,\mu\text{C}$ charge moving from 10 V to 6 V.

$+1.0\times10^{-5},\text{J}$

$-1.0\times10^{-5},\text{J}$

$-1.0\times10^{-6},\text{J}$

$-4,\text{V}$

Explanation

This question tests AP Physics C skills in understanding electric potential energy within electric fields. Electric potential energy (U) is the energy a charge has due to its position in an electric field, calculated by U = qV. In this scenario, the positive charge moving from 10 V to 6 V experiences a potential difference of ΔV = 6 - 10 = -4 V. The correct answer, A, is derived by applying ΔU = qΔV = (2.5×10⁻⁶ C)(-4 V) = -1.0×10⁻⁵ J. A common distractor, B, arises from sign confusion when potential decreases. To assist students, emphasize that positive charges lose energy when moving to lower potentials, and practice calculating potential differences as final minus initial values.

6

In the context of the electric field, calculate the change in electric potential energy for a $+1.0,\mu\text{C}$ charge moved 0.50 m across a uniform $200,\text{V/m}$ field.

$+2.0\times10^{-4},\text{J}$

$-1.0\times10^{-4},\text{J}$

$+1.0\times10^{-4},\text{J}$

$+100,\text{V}$

Explanation

This question tests AP Physics C skills in understanding electric potential energy within electric fields. Electric potential energy (U) is the energy a charge has due to its position in an electric field, calculated by U = qV. In this scenario, the charge moved 0.50 m across a 200 V/m field, experiencing a potential difference of ΔV = -Ed = -200 × 0.50 = -100 V (negative because moving along field direction). The correct answer, B, is derived by applying ΔU = qΔV = (1.0×10⁻⁶ C)(-100 V) = -1.0×10⁻⁴ J. A common distractor, A, arises from sign confusion about field direction. To assist students, emphasize that "across" typically means along the field direction (high to low potential), and practice visualizing field lines and equipotential surfaces.

7

Based on the scenario, calculate the change in electric potential energy for a $+2.0,\mu\text{C}$ charge moving 0.30 m along a uniform $400,\text{V/m}$ field between capacitor plates.

$+240,\text{J}$

$+2.4\times10^{-4},\text{J}$

$+0.24,\text{J}$

$-2.4\times10^{-4},\text{J}$

Explanation

This question tests AP Physics C skills in understanding electric potential energy within electric fields. Electric potential energy (U) is the energy a charge has due to its position in an electric field, calculated by U = qV. In this scenario, the charge moving 0.30 m along a 400 V/m field experiences a potential difference of ΔV = -Ed = -400 × 0.30 = -120 V (negative because moving along the field direction decreases potential). The correct answer, D, is derived by applying ΔU = qΔV = (2.0×10⁻⁶ C)(-120 V) = -2.4×10⁻⁴ J. A common distractor, A, arises from forgetting the negative sign when moving along the field direction. To assist students, emphasize that positive charges lose potential energy when moving along electric field lines, and practice identifying the sign of potential changes based on movement direction relative to the field.

8

Based on the scenario, calculate the change in electric potential energy for a $+6.0,\mu\text{C}$ charge moved through a $-8,\text{V}$ potential difference.

$-8,\text{J}$

$-4.8\times10^{-6},\text{J}$

$+4.8\times10^{-5},\text{J}$

$-4.8\times10^{-5},\text{J}$

Explanation

This question tests AP Physics C skills in understanding electric potential energy within electric fields. Electric potential energy (U) is the energy a charge has due to its position in an electric field, calculated by U = qV. In this scenario, the positive charge experiences a potential difference of ΔV = -8 V (given directly). The correct answer, A, is derived by applying ΔU = qΔV = (6.0×10⁻⁶ C)(-8 V) = -4.8×10⁻⁵ J. A common distractor, B, arises from misunderstanding that a negative potential difference means the charge moves to a lower potential. To assist students, emphasize that potential difference signs indicate direction of change, and positive charges lose energy when experiencing negative potential differences.