Physics 2

“Two charges are placed at different positions — what is the direction of the electric field at a point?”

• Draw a dot where the field is asked.

• For each charge:

  • Positive → field points away

  • Negative → field points toward

• Draw arrows from the point, one for each contribution.

• Break each arrow into x and y components.

• Add components:

  • Ex=∑ExE_x = \sum E_xEx​=∑Ex​

  • Ey=∑EyE_y = \sum E_yEy​=∑Ey​

• Combine into a final direction:

  • Quadrant tells you the answer

“Find the electric potential at a point from multiple charges.”

1. Use the scalar formula — no directions:

   V=∑kQrV = \sum k\frac{Q}{r}V=∑krQ​

2. Compute distance from the point to each charge.

3. Add all contributions with signs:

   • charge → + potential

   • – charge → – potential

4. Compare to answer choices.

“Find net electric force on a point charge from other charges.”

“Energy change when a charge moves from r₁ to r₂.”

“Gauss’s Law — find charge enclosed inside a spherical Gaussian surface.”

“Electric flux through a surface when E = Ax + By + Cz.”

“Find charge enclosed using divergence of E.”

“Circuit current relationship at a junction (KCL).”

“Inductor voltage long after switch closes.”

“Electric field from a uniformly charged rod at a point along its axis.”

“Capacitor attached to a resistor or battery — how does Q change when geometry changes?”

“Determine charge sign and magnitude from particle curvature in magnetic field.”

“Field from infinite sheet(s) of charge.”