Velocity v = fλ constant for given medium. Ultrasound has higher frequency (>20 kHz) than audible sound, so wavelength λ = v/f is smaller. Typical ultrasound in MHz range, λ in mm.
Explanation:
An AC generator uses continuous 'slip rings' which allow the output polarity to reverse every half-rotation of the coil, generating alternating current. To produce direct current (DC), the slip rings must be replaced by a 'split-ring commutator'. This commutator reverses the connections to the external circuit at the exact moment the coil's current reverses, ensuring current flows in only one direction outside.
Explanation:
Time period T = 1/f = 1/200 = 0.005 s = 5 ms. Frequency is number of cycles per second. Relationship T = 1/f is fundamental. For 200 Hz, period is 5 milliseconds.
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