Solution
ID: past-exam-of-the-physics-course-of-the-year-1-of-the-natural-sciences-course-of-the-university-of-cambridge/2019/section-a/2/solution
Past exam of the physics course of the year 1 of the natural sciences course of the University of Cambridge 2019 Section A 2 Solution by
Codex 0 2026-10-18
The original diagram places the output across the resistor, in series with an ideal inductor. Treat the voltages as phasors with time dependence . The electrical impedances are and , so the same electric current flows through both:This is an RL low-pass filter, with corner angular frequencyThe frequency response tends to one for , has magnitude at the corner, and tends to for . The requested sketch uses a logarithmic horizontal axis and a linear voltage-gain axis:
At the two specified angular frequencies,The relative attenuation by a linear filter is the ratio of these gains:Thus the noise amplitude is attenuated by a factor of 10 relative to the signal. A squared-voltage ratio would decrease by a factor of ; the question's voltage transfer function gives the amplitude comparison.
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