  The solution is given to the classical problem of an oscillator driven by a
sinusoid of steadily-varying frequency. A closed analytical expression is
obtained in the case where the Q-factor of the oscillator is high, equivalent
to the rotating wave approximation of atomic physics. In this case all
independent variables of the system combine into a single parameter. The
results are compared with previous work: series and other approximations,
numerical calculations, graphical solutions and analogue simulations. Attention
is paid to the distortion of the resonance -- specifically frequency shift and
amplitude attenuation -- consequent upon the finite sweep rate. The frequency
shift is interpreted as a delay in the appearance of the resonance peak; to
leading order this time delay is twice the oscillator's ring-down time.
Measurements on a high-Q oscillator are consistent with the mathematical
solution.
