1. A harmonic oscillator has a period of vibration of 4 second.a)what is the frequency of vibration?b)how many times does the harmonic oscillator pass its starting point in 1 minute?2. take a wave of infrared radiation of wavelength 1.0×10-3 cm. If the amplitude of the wave =0 at time t=0 . what fraction of the maximum amplitude the wave possess at time t= 16.68 second? (show calculation).3. radiation of wavelength 620 nm passes through 2 small slits that are 1 cm apart. Will waves that are diffracted by 60 dgree on the same direction from the two slits completely reinforce each other?(show calculation).4. calculate the velocity of photoelectrons ejected from a sodium metal surface. with work function of 2.46 eV by ultraviolet light of wavelength 250 nm ?