A bench supply has a transformer winding of rms at (sinusoidal

PHYSICS · Multi-part · Fermi University Physics · Electricity, Magnetism & Electromagnetism · Electromagnetic induction and alternating-current circuits · Electromagnetic induction and alternating-current circuits

Electricity, Magnetism and Electromagnetism, Ch Alternating current: peak and rms values, the oscilloscope and rectification

Problem

A bench supply has a transformer winding of

24.0\,\mathrm{V}

rms at

50\,\mathrm{Hz}

(sinusoidal, negligible winding resistance), a bridge of four ideal diodes (no forward voltage drop, no reverse current) and a smoothing capacitor

C = 4700\,\mu\mathrm{F}

. The load is a coil of constantan wire of resistivity

\rho_{\mathrm{r}} = 4.9\times10^{-7}\,\Omega\,\mathrm{m}

, length

12.0\,\mathrm{m}

and diameter

0.50\,\mathrm{mm}

, of temperature-independent resistance. ((a)) Find the resistance of the load. ((b)) Find the mean power the load would dissipate if it were connected directly across the winding. ((c)) With the rectifier and capacitor in place, and taking the load current as steady and equal to (peak output voltage)/(resistance), estimate the peak-to-trough ripple voltage. ((d)) The mains is now switched off at an instant when the capacitor is charged to the peak output voltage. How long after that does the output fall to half the peak voltage?

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