Modern Physics — Chapter quiz · Physics & Environmental Science, Grade 12

Compare wave–particle evidence, relativistic limits, and nuclear mass-energy accounting.

Problem 1

Which model of light best explains the photoelectric effect?
  1. the ray model
  2. the wave model
  3. the longitudinal model
  4. the particle (photon) model
Answer and explanation

the particle (photon) model

The photoelectric effect requires the particle model — light delivers energy in discrete photons.

Problem 2

A photon has a frequency of 2 × 10¹⁵ Hz. Using h = 6.63 × 10⁻³⁴ J·s, find its energy in joules.
Answer and explanation

1.326e-18 J

E = h f = (6.63 × 10⁻³⁴) × (2 × 10¹⁵) = 1.326 × 10⁻¹⁸ J.

Problem 3

Kmax=2.5 eV. Find electron stopping potential.
Hints

Write the relationship first; substitute with consistent units.

Answer and explanation

2.5 V

eVstop=Kmax.

Problem 4

What changes when above-threshold light intensity increases at fixed frequency?
Answer and explanation

More emitted electrons generally occur; maximum kinetic energy does not increase in the simple model.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the calculation or mechanism that supports it.
  • Include units, conditions, or limits where relevant.

Problem 5

Independent chapter check: A material has work function2.2 eV. Photons carry3.7 eV. Find Kmax in eV and joules, and stopping-potential magnitude.
Answer and explanation

Kmax=1.5 eV=2.403×10⁻¹⁹ J; stopping-potential magnitude=1.5 V. At fixed photon energy, increasing intensity changes available electron number rather than this maximum.

Kmax=1.5 eV=2.403×10⁻¹⁹ J; stopping-potential magnitude=1.5 V.

At fixed photon energy, increasing intensity changes available electron number rather than this maximum.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the physical or environmental mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

Problem 6

v=.80c gives√(1−v²/c²)=.60. Find γ.
Hints

Write the relationship first; substitute with consistent units.

Answer and explanation

1.6667

1/.60≈1.667.

Problem 7

What must be specified in a time-dilation calculation?
Answer and explanation

The events, proper-time clock, relative speed, and inertial reference frames.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the calculation or mechanism that supports it.
  • Include units, conditions, or limits where relevant.

Problem 8

Independent chapter check: A process has proper duration3.0 μs and moves at0.80c relative to a lab. Find γ and lab duration; a rest10 m object moving parallel at that speed has what lab length?
Answer and explanation

γ=1/√0.36=5/3. Lab duration=5.0 μs; length=10/(5/3)=6.0 m, with simultaneous endpoints in the lab.

γ=1/√0.36=5/3.

Lab duration=5.0 μs; length=10/(5/3)=6.0 m, with simultaneous endpoints in the lab.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the physical or environmental mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

Problem 9

A.005u rest-mass loss gives energy at 931.5 MeV/u. Find it.
Hints

Write the relationship first; substitute with consistent units.

Answer and explanation

4.6575 MeV

.005×931.5.

Problem 10

Why can different detectors register different counts from one source?
Answer and explanation

Geometry, efficiency, energy response, shielding, and background differ.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the calculation or mechanism that supports it.
  • Include units, conditions, or limits where relevant.

Problem 11

Independent chapter check: A supplied reaction releases0.0015 u of rest-mass equivalent per event. Estimate energy in MeV, then explain why a detector count rate cannot directly give absorbed dose.
Answer and explanation

Energy≈0.0015×931.5=1.397 MeV/event. Dose also needs energy deposited, exposed mass, radiation characteristics and geometry; count rate includes detector efficiency/background and is not dose.

Energy≈0.0015×931.5=1.397 MeV/event.

Dose also needs energy deposited, exposed mass, radiation characteristics and geometry; count rate includes detector efficiency/background and is not dose.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the physical or environmental mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

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