Question

7. Radiowaves are about 1m long. Convert this to frequency, in MHz. 8. When sodium compounds are heated in a bunsen burner flame, they emit light at a wavelength of 5890 A. If 1.0 x 10 mole of sodium atoms each emit a photon of this wavelength, how many kilojoules of energy are emitted? 9. An alpha particle of mass 4.0026 amu has a velocity of 10.0% of the speed of light. What is its de Broglie wavelength (in m)? 10. The orientation in space of an orbital is designated by which quantum number? a) n b) m c) mi d) y e)

Answer 1

7.

Wavelength of radio wave, $\lambda$ = 1 m

Frequency,

$\nu = \frac{c}{\lambda }$

where,

c = speed of light in vacuum = 3 x 10⁸ m/s

Thus,

$\nu$ = 3 x 10⁸ m/s / 1 m

    = 3 x 10⁸ s^-1

    = 3 x 10⁸ Hz         ($\because$ 1 Hz = 1 s^-1)

    = 3 x 10² MHz      ($\because$1 MHz (megahertz) = 10⁶ Hz)