AP Physics 2 practice questions and exam guide

A point charge +Q sits at the center of a Gaussian sphere of radius r. By Gauss's law, the flux through the sphere is:

1. Q/(4πε₀)
2. kQ/r²
3. Zero
4. Q/ε₀ — independent of r

Answer: D — Q/ε₀ — independent of r

D) Gauss: Φ = Q_enc/ε₀, independent of r. A/B) Mix up potential or field formulas. C) Only if Q_enc = 0.

Resistors R₁ and R₂ in PARALLEL combine to:

1. 1/R = 1/R₁ + 1/R₂ (parallel always gives R less than smallest individual)
2. R = R₁ + R₂
3. R = R₁·R₂
4. R = √(R₁·R₂)

Answer: A — 1/R = 1/R₁ + 1/R₂ (parallel always gives R less than smallest individual)

Series: R_total = R₁ + R₂ + ... (current shared, voltage divided). Parallel: 1/R_total = Σ 1/R_i (voltage shared, current divided). Two-resistor parallel shortcut: R = R₁R₂/(R₁+R₂). Add a parallel resistor → total R drops.

A submerged object experiences a buoyant force equal to:

1. Its own weight
2. The weight of the fluid displaced — Archimedes' principle. If buoyancy > weight: floats. If less: sinks. If equal: neutrally buoyant.
3. Atmospheric pressure
4. Zero

Answer: B — The weight of the fluid displaced — Archimedes' principle. If buoyancy > weight: floats. If less: sinks. If equal: neutrally buoyant.

F_buoy = ρ_fluid · V_displaced · g. Floats when ρ_object < ρ_fluid. Ice floats on water (ρ_ice ≈ 0.92 g/cm³). Submarines change buoyancy by flooding/blowing ballast. AP-favorite numerical setup.

Two streamlines pass through a horizontal pipe. The one going through a constriction has a:

1. Higher pressure and higher speed
2. Lower pressure and lower speed
3. Higher pressure and lower speed
4. Lower pressure and higher speed — Bernoulli + continuity

Answer: D — Lower pressure and higher speed — Bernoulli + continuity

D) Continuity: narrower ⇒ faster. Bernoulli: faster ⇒ lower P. A) Both wrong. B) Wrong on speed. C) Static-fluid intuition incorrect for flow.

A solid object weighs 50 N in air and 30 N when fully submerged in water. The buoyant force on it is:

1. 80 N
2. 30 N (the apparent weight)
3. 50 N (the actual weight)
4. 20 N — the difference (apparent weight loss)

Answer: D — 20 N — the difference (apparent weight loss)

D) Buoyant force = weight in air − apparent weight in water = 50 − 30 = 20 N. A) Wrong sign. B/C) Confuse buoyancy with weight values.

A ray strikes a plane mirror at 35° from the normal. The reflected ray makes:

1. 55° with the mirror surface
2. 35° with the normal — half-right ray-tracing if measured from surface
3. 35° from the mirror's surface (common ray-tracing slip)
4. 70° from the normal

Answer: B — 35° with the normal — half-right ray-tracing if measured from surface

B) Law of reflection: equal angle from the normal. A) Equivalent statement (the complement) — accept partial credit conceptually but C is the common slip. C) Mistakes 'from surface' for 'from normal' — a half-right ray-tracing error. D) Doubles the angle.

The second law of thermodynamics implies that, for an isolated system:

1. Energy is destroyed
2. Heat moves from cold to hot reservoirs spontaneously
3. The entropy of the universe never decreases — heat flows from hot to cold spontaneously and no heat engine can be 100% efficient
4. Pressure stays constant

Answer: C — The entropy of the universe never decreases — heat flows from hot to cold spontaneously and no heat engine can be 100% efficient

C) Standard formulation. A/B/D) Each contradicts the second law.

Coulomb's law: the electric force between two point charges q₁ and q₂ separated by r is:

1. F = k·|q₁q₂|/r², with k ≈ 8.99 × 10⁹ N·m²/C² — attractive if opposite, repulsive if same sign
2. F = mg
3. F = qE only
4. F = q²

Answer: A — F = k·|q₁q₂|/r², with k ≈ 8.99 × 10⁹ N·m²/C² — attractive if opposite, repulsive if same sign

Coulomb's law: inverse-square (analog of gravity), but charges can repel as well as attract. k = 1/(4πε₀). Vector quantity — superposition for multi-charge systems. Foundation for electric field (E = F/q).

An ideal gas at fixed volume is heated. Its internal energy:

1. Decreases
2. Becomes zero
3. Stays the same
4. Increases — for ideal gas U depends only on T

Answer: D — Increases — for ideal gas U depends only on T

D) Ideal gas: U ∝ T. Heat at constant V goes entirely to ΔU. A/B/C) Contradict ideal gas.

Kirchhoff's voltage law (KVL) states:

1. Current is conserved at nodes (that's KCL)
2. Voltage equals current
3. Resistors must be in parallel
4. Sum of voltage changes around any closed loop equals zero (conservation of energy applied to circuits)

Answer: D — Sum of voltage changes around any closed loop equals zero (conservation of energy applied to circuits)

Kirchhoff's two laws: KCL (current in = current out at any node — charge conservation) and KVL (sum of ΔV around any loop = 0 — energy conservation). Used to solve complex circuits via simultaneous equations.

For the image in the previous problem, magnification is:

1. +2 (upright, enlarged)
2. −2 — inverted, twice the height (M = −d_i/d_o)
3. +0.5
4. Undefined

Answer: B — −2 — inverted, twice the height (M = −d_i/d_o)

B) M = −60/30 = −2 (inverted, 2× height). A) Misses inversion. C) Inverted ratio. D) Defined.

In a nuclear fission reaction (e.g., U-235 + neutron → Ba + Kr + neutrons + energy), the mass of the products is:

1. Equal to the reactants
2. LESS than the reactants — the missing mass is converted to energy via E = Δm·c² (mass defect)
3. Greater than the reactants
4. Half the reactants

Answer: B — LESS than the reactants — the missing mass is converted to energy via E = Δm·c² (mass defect)

Nuclear binding energy: total mass of nucleus < sum of individual proton/neutron masses. Mass defect Δm corresponds to binding energy. In fission: heavy nuclei split, releasing the difference. In fusion: light nuclei combine, releasing the difference. Both: E = Δm·c² is enormous (millions of times chemical reactions).

Boyle's Law?

P₁V₁ = P₂V₂ at constant T.

Hydrogen electron transition n=3 → n=1. Photon energy?

E = E_3 − E_1 = (−13.6/9) − (−13.6) = 13.6(1 − 1/9) ≈ 12.1 eV.

Mirror/lens equation?

1/f = 1/d_o + 1/d_i.

What is polarization?

Restricting wave oscillation to one direction. Light from sunlight, screens, glare often polarized.

Conversion: Celsius to Kelvin?

K = °C + 273.15.

Parallel circuit: what's same throughout?

Voltage. Current divides among branches.