PRACTICE COLLECTION / 39 PROBLEMS
Modern physics
Connect photons, matter waves and atomic energies. Each problem includes progressive hints, guided reasoning and a question to test the idea again. Problems marked “Free sample” are complete for everyone; membership opens the rest.
LEARN BEFORE YOU PRACTISE
Build the reasoning first.
Photons, photoelectric emission and matter waves
Separate energy per event from event rate, then connect particle momentum to wavelength.
10 worked examples · 8 checks →Hydrogen levels, spectra and ionization
Read negative bound energies correctly and distinguish a level gap, a threshold and a cascade.
6 worked examples · 7 checks →Radioactive decay, half-life and mean life
Connect survival probability to measured activity, then test the assumptions behind an inferred age.
9 worked examples · 9 checks →Nuclear size, binding and reaction energy
Balance the particles, match the mass convention and include recoil in the energy account.
11 worked examples · 9 checks →Semiconductor junctions, rectifiers and Zener regulation
Explain the carriers, choose a diode model and verify the operating state before trusting the output.
17 worked examples · 15 checks →Logic gates, complete truth tables and useful circuits
Translate the condition, follow intermediate signals and verify every input combination.
8 worked examples · 9 checks →CONCEPTS IN THIS COLLECTION
PRACTISE AT YOUR PACE
Problems in this collection
39 problems · Showing 12
Modern physics
Leave voltage for the current limiter
An LED is not a resistor whose value is V_f/I at all currents; the declared forward-drop model has a limited operating range.
Apply a principleModern physics
An alpha particle removes both proton and neutron counts
How many neutrons remain in the daughter nucleus?
Apply a principleModern physics
Beta decay changes identity without ejecting a nucleon
What is the proton number of the daughter nucleus?
Apply a principleModern physics
After three half-lives, what fraction remains?
What fraction of the parent nuclei remains undecayed on average?
Apply a principleModern physics
Both NAND inputs are high
What is its output?
Apply a principleModern physics
The dark current is not the light signal
What optical power is incident on the detector?
Read graphs & measurementsModern physics
Multiply values from the same load state
What is the largest electrical power demonstrated by these sampled points?
Read graphs & measurementsModern physics
The stopping line reaches zero at the threshold
A measured slope and one point can identify a physical threshold.
Read graphs & measurementsModern physics
Use energy gaps before naming spectral lines
What is λ4→2 divided by λ3→2?
Compare casesModern physics
A band gap sets an absorption energy threshold
What is the longest vacuum wavelength whose photon energy can bridge this gap?
Apply a principleModern physics
Compare complete rest masses in a fission channel
What energy is released in this channel?
Apply a principleModern physics
Account for the binding already present in the fuel
What is the reaction energy release under these rounded values?
Connect concepts12 of 39 shown