John Abbott College · 203-SN3-RE

John Abbott 203-SN3-RE: Waves and Modern Physics Tutoring

Wave questions often become easier once you decide what is oscillating, how it travels and which quantities stay fixed. Modern physics adds a different challenge: choosing when a wave description is useful and when photon energy matters. Nablio helps you connect these ideas to equations and work through the parts of your current 203-SN3-RE problems that you find difficult.

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What we can work on

Oscillations and travelling waves: interpret amplitude, period, frequency, wavelength and wave speed.
Waves on strings and in air: connect the physical setup to a wave model.
Optics: reason through interference and diffraction patterns.
Modern physics: connect photon and matter-wave ideas to introductory atomic and nuclear questions.

Choose the model before the formula

For a wave question, list the known quantities and ask whether the source frequency, medium or boundary conditions have changed. For a photon, use $E=hf=hc/\lambda$ , where $E$ is its energy, $f$ its frequency, $\lambda$ its wavelength in vacuum, $h$ Planck’s constant and $c$ the speed of light in vacuum. Light intensity measures energy arriving per unit area per unit time; it is not the energy of one photon.

Worked example: can this light eject an electron?

Light of wavelength 400 nm illuminates a metal with work function $\phi=2.20\,\mathrm{eV}$ . Find the maximum kinetic energy of emitted electrons and the magnitude of the stopping potential. Use $hc\approx1240\,\mathrm{eV\cdot nm}$ and the introductory single-photon photoelectric model.

Find the energy of one photon: $E=\frac{hc}{\lambda}=\frac{1240}{400}=3.10\,\mathrm{eV}$ .
Compare with the work function. Since 3.10 eV is greater than 2.20 eV, emission is possible.
Let $K_{\max}$ be the greatest kinetic energy of an emitted electron. Subtract the work function, the energy needed to leave the metal: $K_{\max}=E-\phi=3.10-2.20=0.90\,\mathrm{eV}$ .
Let $V_s$ be the positive magnitude of the stopping potential and $e$ the magnitude of the electron’s charge. Use $eV_s=K_{\max}$ . One electronvolt (eV) is the energy change of a charge of magnitude $e$ across one volt. Thus $0.90\,\mathrm{eV}$ corresponds to $V_s=0.90\,\mathrm{V}$ .
Check the threshold wavelength: $\lambda_0=\frac{hc}{\phi}=\frac{1240}{2.20}\approx564\,\mathrm{nm}$ . The incident 400 nm wavelength is shorter, consistent with emission.

At fixed wavelength, increasing intensity can increase the emission rate but does not increase $K_{\max}$ in this model. If each photon is below the work function, higher intensity alone does not overcome the threshold.

Try it yourself

For the same metal, compare light at 500 nm and 600 nm. Does either wavelength cause emission? When emission occurs, find $K_{\max}$ and the stopping-potential magnitude.

Show the explained answer

At 500 nm, $E=1240/500=2.48\,\mathrm{eV}$ , so $K_{\max}=0.28\,\mathrm{eV}$ and $V_s=0.28\,\mathrm{V}$ . At 600 nm, $E\approx2.07\,\mathrm{eV}$ , below 2.20 eV, so no photoelectrons are emitted in this model. Do not report a negative kinetic energy; the negative difference means the threshold was not reached.

Original Nablio example and practice, independent of the college. These are not course assessment questions. Follow your current section’s outline for the material to review.

Optional spring-oscillation practice

If you’re practising spring oscillations for John Abbott’s 203-SN3-RE, this optional worked lesson shows how initial position and velocity determine the motion.

Bring the question and the point of confusion

Bring your diagram, graph or attempted calculation. A session can focus on deciding which model applies, setting up the equation and checking units before moving to a similar problem that you solve yourself.

We use permitted practice without completing graded assignments or exams on your behalf.

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