# The Physical World I

Spring 2005
MWF 11:30

Instructor: Dr. Bruce Law, CW 327, Tel: 532-1618.

# wavelengthA = speed/fA = speed/(2 x fB) = wavelengthB/2 where wavelengthB = speed/fB. Hence the wavelength of source A is half the wavelength of source B.

## E20.6. Wavelength = speed/frequency. The frequency is the same. The electromagnetic wave (light wave) has a higher speed and therefore longer wavelength than a sound wave.

E20.12. Light can travel through a vacuum. Sound needs a medium to travel in.

E20.16. The speed is the same. The wavelength = speed/frequency is halved.

E20.24. (1) Light travels faster than sound therefore you should see the explosion before you hear it and (2) sound cannot travel through a vacuum (i.e. space) therefore in fact you should not hear the explosion!

PROBLEMS OF Home Work 14

P20.1. Wavelength = speed/frequency = 340/340 = 1m.

Wavelength = speed/frequency = 340/34000 = 0.01m.

P20.3. Speed = 1530m/s. Time delay to the ocean floor and back = 6s, therefore, it takes 3s for the sound to reach the ocean floor and 3s for the sound to return. Speed = distance/time therefore distance = speed x time = 1530 x 3 = 4590m is the depth to the ocean floor.