The Physics of Waves: Light Waves, Sound Waves and Ultrasound
A Doppler ultrasound device produces ultrasound of frequency 5 MHz, and the echo from red blood cells has a frequency of 5 002 500 Hz. The beat frequency produced will be:
Inaudible
250 Hz
2500 Hz
0.25 MHz
2500 Hz
Beat frequency is the difference between the two frequencies. 5 000 000โ5 002 500 = 2500 Hz. The frequency of the beats is within the audible range so we can hear them.
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The term “refraction” may be applied to which of the following?A. The effect on light rays as they enter the cornea of the eye
B. Light rays from an object meeting at a point to form a sharp image
C. A light ray travelling away from a surface at the same angle that the light ray approached the surface
D. A light ray travelling through a glass with a faster speed than it would have in air
The unit called the decibel (dB) is used in the measurement of:
A. Sound frequency (pitch)
B. Sound intensity (energy)
C. Sound pressure
D. Sound level (loudness)
In a wave, what is the distance between two adjacent troughs called?
A. The period
B. The displacement
C. The amplitude
D. The wavelength
What will a sound of frequency 250,000 Hz be?
A. Audible
B. Painful to listen to
C. Ultrasonic
D. Close to the threshold of hearing
Visible light waves are examples of:
A. Electromagnetic waves
B. Mechanical waves
C. Longitudinal waves
D. Compressional waves
Which is the BEST definition of a wave?
A. The method by which the energy carried by visible light is propagated.
B. Travelling oscillations in the magnitude and direction of electric and mag-netic fields that do not require a material medium.
C. A periodic disturbance in some property of the medium, the medium itself remains (relatively) at rest.
D. A mechanism for the transfer of energy without the transfer of matter.
Which of the following sound levels, if prolonged, will damage the hearing mechanism of the ear without being perceived as painful?
A. 50 dB
B. 70 dB
C. 90 dB
D. 120 dB
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