AP Physics Physics: Thermodynamics & Modern Physics 3

Question 1

According to de Broglie's hypothesis, what is the wavelength of a particle with momentum p?

Accepted Answer

λ = h/p

Answer

De Broglie's relation gives the matter wavelength as λ = h/p, where h is Planck's constant.

Question 2

In nuclear fission, when a heavy nucleus splits, the products have:

Accepted Answer

Less total mass than the original nucleus

Answer

Mass-energy equivalence (E=mc²) means the mass defect is converted to kinetic energy of the fragments.

Question 3

A gas expands adiabatically against zero external pressure (free expansion). What is true?

Accepted Answer

Both Q and W equal zero

Answer

In free expansion, no heat is exchanged (adiabatic) and no work is done (P_ext = 0), so Q = W = 0 and ΔU = 0.

Question 4

The Heisenberg Uncertainty Principle states that:

Accepted Answer

The position and momentum of a particle cannot both be precisely known simultaneously

Answer

Heisenberg's principle states Δx·Δp ≥ ℏ/2, meaning precise knowledge of position limits precision of momentum and vice versa.

Question 5

Which process results in a net decrease in entropy of the universe?

Accepted Answer

No real process can cause a net decrease in entropy of the universe

Answer

The Second Law of Thermodynamics prohibits any process from decreasing the total entropy of the universe.

AP Practice Test