Advanced physics – AC circuits, medical imaging, quantum physics
PhysicsQuantum & Nuclear PhysicsAges 17–18
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Sign in to playThree physics topics in one simulation, chosen with the topic parameter. Alternating current: a series R, L, C circuit with out-of-phase u and i graphs, a phasor diagram, and the resonance curve of I versus frequency. Physics in medical diagnosis: an X-ray beam passing through soft tissue and bone to form a radiograph following the absorption law I = I₀e^(−μx), or an ultrasound pulse reflecting at a boundary to measure depth. Quantum physics: light of a chosen wavelength shines on a metal, showing whether the photoelectric effect occurs and the maximum initial kinetic energy of the ejected electrons.
Lesson: Alternating current; physics in medical diagnosis; quantum physics
What it shows
Three topics from applied and modern physics are modelled side by side. The AC topic is a series RLC circuit: inductive reactance ωL rises and capacitive reactance 1/(ωC) falls with frequency, and at f₀ = 1/(2π√(LC)) they cancel, so the impedance equals R and the current peaks in phase with the voltage. The medical topic applies exponential X-ray absorption, I = I₀e^(−μx), and ultrasound echo timing, t = 2d/v. The quantum topic shows the photoelectric effect: electrons are emitted only if the photon energy hc/λ exceeds the work function of the metal.
How to use
Pick a topic with the tabs. In Alternating current, drag across the graph to change the frequency while watching the phasor diagram and the I–f curve, then press Set to resonance frequency; change Circuit resistance R to compare peak shapes. In Medical diagnosis, use Switch to ultrasound and Switch to X-ray to compare the two methods. In Quantum physics, drag to change the wavelength and press Change metal to compare potassium, zinc and silver.
Parameters you can change
- Current topic 1. Alternating current (RLC circuit), 2. Physics in medical diagnosis, 3. Quantum physics (photoelectric effect)
- AC frequency 10–200 Hz
- Circuit resistance R 5–200 Ω
- Diagnostic method X-ray imaging (X-ray absorption), Ultrasound (sound wave reflection)
- Wavelength of light shone on the metal 200–700 nm
- Cathode metal Potassium (work function 2.25 eV), Zinc (work function 3.55 eV), Silver (work function 4.78 eV)
Questions to explore
- At the resonance frequency, what is the phase difference between u and i, and why is the current largest?
- How does increasing R change the height and sharpness of the peak on the I–f graph?
- For 400 nm light, which of potassium, zinc and silver emit electrons, and what is each threshold wavelength?
