An ideal voltmeter has infinite resistance, ensuring that it does not draw any current from the circuit and provides an accurate voltage reading.
Explain the construction of a spherical wavefront by using Huygens' principle.
The slope of the tangent to the curve \( x = \sin\theta \) and \( y = \cos 2\theta \) at \( \theta = \frac{\pi}{6} \) is ___________.