GED Science Practice Test: Measuring Waves
A number of characteristics of waves can be measured. As we are mostly interested in infrared radiation as a type of heat transfer, we will focus on the characteristics of transverse waves. These characteristics of transverse waves tell us something about the energy within those waves. The following diagram shows some features of transverse waves:
The amplitude of a wave refers to the maximum amount of displacement of a particle on the medium from its rest position. In a sense, the amplitude is the distance from rest to crest. Similarly, the amplitude can be measured from the rest position to the trough position. The higher the amplitude, the more energy a wave contains.
The wavelength of a wave is simply the length of one complete wave cycle. A wavelength is measured from crest to crest, or from trough to trough. The shorter the wavelength, the more energy a transverse wave has.
The frequency and period of a wave are different, but related quantities that can be measured for a wave. Frequency refers to the rate at which something happens. Period refers to the time it takes something to happen. The period of a wave is the time for it to make one complete vibrational cycle – e.g. from the crest of one wave to the crest of the next. The frequency is the rate at which waves pass a given point. Frequency is the number of cycles/second, and is measured in Hertz (Hz), where 1 cycle/second = 1Hz. Conversely, period is the number of seconds/cycle. The higher the frequency of a wave, the more energy it has.
To imagine the distinction and the relatedness of frequency and period, think about a woodpecker that drums upon a tree at a periodic rate. If the woodpecker drums upon a tree 2 times in one second, then the frequency is 2 Hz. Each drum must endure for one-half a second, so the period is 0.5 s. If the woodpecker drums upon a tree 4 times in one second, then the frequency is 4 Hz; each drum must endure for one-fourth a second, so the period is 0.25 s. If the woodpecker drums upon a tree 5 times in one second, then the frequency is 5 Hz; each drum must endure for one-fifth a second, so the period is 0.2 s. Do you observe the relationship? The period is the reciprocal of the frequency and vice versa. In equation form, this is expressed as follows.
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