Fiveable
💡AP Physics C: E&M
​

💡AP Physics C: E&M

FRQ 4 – Qualitative/Quantitative Translation
​
Unit 8: Electric Charges, Fields, and Gauss's Law
​
FRQ Types & Units

Each FRQ type tests specific skills taught in particular units. Here's why certain units appear for each question type:

This mapping reflects College Board's exam structure - each FRQ type tests specific skills that are taught in particular units.

Practice FRQ 1 of 201/20

4. A solid, nonconducting (insulating) sphere of radius R=0.050 mR=0.050\ \text{m}R=0.050 m is centered at the origin. The sphere has a uniform volume charge density ρ=+6.0×10−6 C/m3\rho=+6.0\times10^{-6}\ \text{C/m}^3ρ=+6.0×10−6 C/m3. The region r<Rr<Rr<R is filled with a dielectric material of permittivity ε1=2.0ε0\varepsilon_1=2.0\varepsilon_0ε1​=2.0ε0​, and the region r>Rr>Rr>R is vacuum with permittivity ε0\varepsilon_0ε0​. A small test particle of mass m=2.0×10−4 kgm=2.0\times10^{-4}\ \text{kg}m=2.0×10−4 kg and charge q=−3.0×10−9 Cq=-3.0\times10^{-9}\ \text{C}q=−3.0×10−9 C is placed at rest at point PPP on the +x-axis at r=0.030 mr=0.030\ \text{m}r=0.030 m. Gravitational effects are not negligible. Figure 1 shows the experimental setup.

Figure 1. Uniformly charged insulating sphere with dielectric interior; test particle at point P inside the sphere; concentric Gaussian surface of radius r.

Figure 1
A.

At point PPP, the magnitude of the electric force on the test particle is FEF_EFE​ and the magnitude of the gravitational force on the test particle is FgF_gFg​.

Indicate whether FEF_EFE​ is greater than, less than, or equal to FgF_gFg​ by writing one of the following.

  • FE>FgF_E > F_gFE​>Fg​
  • FE<FgF_E < F_gFE​<Fg​
  • FE=FgF_E = F_gFE​=Fg​

Justify your answer.

B.

Derive an expression for the magnitude EPE_PEP​ of the electric field at point PPP (where r=0.030 m<Rr=0.030\ \text{m} < Rr=0.030 m<R) in terms of ρ\rhoρ, rrr, ε1\varepsilon_1ε1​, and physical constants, as appropriate. Begin your derivation by writing a fundamental physics principle or an equation from the reference information. Your final expression should be valid for any point inside the sphere (any r<Rr<Rr<R).

Figure 2. Modified interior permittivity; same geometry and point P; Gaussian surface at r = 0.030 m.

Figure 2
C.

Indicate whether FE, newF_{E,\,new}FE,new​ is greater than, less than, or equal to FEF_EFE​ by writing one of the following. Later, the dielectric material inside the sphere is replaced with a different dielectric with permittivity ε2=4.0ε0\varepsilon_2=4.0\varepsilon_0ε2​=4.0ε0​, while the charge density remains uniform at ρ=+6.0×10−6 C/m3\rho=+6.0\times10^{-6}\ \text{C/m}^3ρ=+6.0×10−6 C/m3 and the radius remains R=0.050 mR=0.050\ \text{m}R=0.050 m. The test particle is again placed at rest at the same point PPP (still at r=0.030 mr=0.030\ \text{m}r=0.030 m). Let FE, newF_{E,\,new}FE,new​ be the new magnitude of the electric force on the test particle at PPP.

  • FE, new>FEF_{E,\,new} > F_EFE,new​>FE​
  • FE, new<FEF_{E,\,new} < F_EFE,new​<FE​
  • FE, new=FEF_{E,\,new} = F_EFE,new​=FE​

Briefly justify your answer by referencing your derivation in part B. Figure 2 shows the modified setup.

Timed

00:00

Response auto-saves






Pep

essential ap study content awaits..

Features
Testimonials
Testimonials
start studying →
FRQ Directions
Free Response Question Practice

This practice environment simulates the AP AP Physics C: E&M Free Response Questions section. Here are some guidelines:

  • Read each question carefullybefore responding. Pay attention to command verbs like "identify," "explain," "analyze," or "evaluate."
  • Use the timer to practice time management. You can pause, restart, or hide the timer as needed.
  • Mark for Review if you want to come back to a question later.
  • Your responses are saved automatically as you type. You can also use the drawing tool for questions that require diagrams or graphs.
  • Use the toolbar for formatting options like bold, italic, subscript, and superscript.
  • Navigate between questions using the Previous and Next buttons at the bottom of the screen.

Tip: Answer all parts of each question. Partial credit is often available, so even if you are unsure, provide what you know.