Diffraction refers to various phenomena which occur when a wave encounters an obstacle or a slit. Diffraction arises because of the way in which waves propagate; this is described by the Huygens–Fresnel principle and the principle of superposition of waves. The above shows a single-slit diffraction in a ripple tank, where the vibrations of the water were observed at positions \(P\) and \(Q\) but not at position \(R.\) If we want to observe the vibrations of the water at position \(R,\) which of the following methods should be used?
a) Make the slit narrower.
b) Make the water of the ripple tank deeper.
c) Increase the frequency of the water wave.