AP Physics Physics: Electricity & Magnetism 4

Question 1

An RC circuit has resistance R and capacitance C. The time constant τ represents the time for the capacitor to charge to approximately what fraction of its maximum charge?

Accepted Answer

63%

Answer

After one time constant τ = RC, the charge reaches Q₀(1 − e⁻¹) ≈ 0.632 Q₀, or about 63% of maximum.

Question 2

A uniform electric field E points in the +x direction. The electric potential V decreases most rapidly in the:

Accepted Answer

+x direction

Answer

The electric field points in the direction of greatest decrease in potential, so potential decreases most rapidly in the +x direction (direction of E).

Question 3

Which Maxwell equation describes the fact that magnetic monopoles do not exist?

Accepted Answer

∇·B = 0

Answer

∇·B = 0 (Gauss's Law for magnetism) states that the net magnetic flux through any closed surface is zero, implying no magnetic monopoles.

Question 4

A wire of length L carrying current I is placed in a uniform magnetic field B perpendicular to the wire. The magnitude of the force on the wire is:

Accepted Answer

BIL

Answer

The force on a current-carrying wire is F = BIL sin θ; with θ = 90°, F = BIL.

Question 5

Two capacitors C₁ = 3 μF and C₂ = 6 μF are connected in series. The equivalent capacitance is:

Accepted Answer

2 μF

Answer

For series capacitors: 1/C_eq = 1/3 + 1/6 = 1/2, so C_eq = 2 μF.

AP Practice Test

AP Practice Test

AP Physics Physics: Electricity & Magnetism 4