8. Ultrasonic waves have frequencies too high to be detected by the human ear but can be produced and detected by vibrating crystals. Calculate the wavelength of an ultrasonic wave of frequency 5.0 x104 s-1 that is propagating through a sample of water at a speed of
1.5 x 103 m s-1. Explain why ultrasound can be used to probe the size and position of the fetus inside its mother's abdomen. Could audible sound with a frequency of 8000 s-1 be used for this purpose?
To calculate the wavelength, we must use the equation that states the speed of sound through a medium is a product of its wavelength and frequency.
c = wavelength x frequency
wavelength = c
= 1.5 x 103 m s-1
5.0 x 104 s-1
= 3.0 x 10-2 m
This is used for probing the uterus while within the mother because the frequency is so high that it penetrates through the body. The low wavelength and high frequency allows the wave to go through the cells and to map out the inside of the mother's abdomen. A sound wave with a frequency even high than the one used in the calculations would also work just as well.
15. Excited lithium atoms emit light strongly at a wavelength of 671 nm. This emission predominates when Li atoms are excited in a flame. Predict the color of the flame.
When the wavelength of a light is 671 nm, the color of that light is a yellowish orange. This is derived from the the visible spectrum of light.