A capacitor consists of two metal surfaces separated by an electrical insulator with no electrically conductive path through it. Why does a current flow in a resistor-capacitor circuit when the switch is closed?

Displacement current flows in the dielectric material(insulated region)

Explanation:

Firstly a capacitor stores charge when a capacitor is charging (or discharging), current flows in the circuit. Also, there is no charge transfer in the dielectric material in the capacitor which is contradictory to the flow of current. Hence, displacement current is the current in the insulated region due to the changing electric flux.

Wavelength and frequency are inversely related, meaning that if you increase the frequency, the wavelength decreases, and if you decrease the frequency, the wavelength increases. This means that we only can think in of these two to change (because the other changes along with it) I will select the frequency.

Now, let's think about the sound, suppose you have a given wave if you increase the frequency, then the pitch of the sound also increases, and you have a "higher" sound, if you decrease the frequency, you have a "lower" sound, more bass.

For the visible light, if you decrease the frequency of a wave, the energy increases, and the light turns to the blue side of the spectrum if you increase the frequency, the light turns more reddish, and the energy decreases.