The velocity of $\alpha-$rays is approximately

Chlorophyll in green plants absorbs light of frequency $4.620 \times 10^{14} \ Hz$. Find the wavelength and the region in the electromagnetic spectrum.

Explain the visible spectrum and the continuous spectrum.

The work functions $(W_0)$ of $K, Na, Li, Mg$ and $Cu$ are $2.25, 2.30, 2.42, 3.70$ and $4.80 \ eV$ respectively. How many of these metals do not undergo photoelectric effect when a radiation of wavelength $450 \ nm$ is allowed to fall on them? $(1 \ eV = 1.602 \times 10^{-19} \ J)$

Explain emission and absorption spectra.

The frequency of an electromagnetic radiation is $2 \times 10^6 \ Hz$. What is its wavelength in metres? (Velocity of light $= 3 \times 10^8 \ m \ s^{-1}$)