Question

Difficulty: MediumElectromagnetic Waves and Electromagnetic Spectrum

A marine navigational radar system emits electromagnetic pulses with a wavelength of 3.0 cm3.0\text{ cm}. Given that the speed of electromagnetic waves in air is 3.0×108 m/s3.0 \times 10^8\text{ m/s}, what is the frequency of the radar signal in gigahertz (GHz\text{GHz})?

Answer: 10 GHz

Answer

The frequency of the radar signal is 10 GHz10\text{ GHz}.
Converting 3.0 cm3.0\text{ cm} to meters gives λ=0.03 m\lambda = 0.03\text{ m}. Using f=c/λf = c / \lambda, f=(3.0×108 m/s)/0.03 m=1.0×1010 Hzf = (3.0 \times 10^8\text{ m/s}) / 0.03\text{ m} = 1.0 \times 10^{10}\text{ Hz}. Dividing by 109 Hz/GHz10^9\text{ Hz/GHz} yields 10 GHz10\text{ GHz}.

Step-by-Step Solution

1
Convert the given wavelength into fundamental SI units (meters).
λ=3.0 cm=3.0×102 m\lambda = 3.0\text{ cm} = 3.0 \times 10^{-2}\text{ m}
The speed of light cc is given in meters per second, so the wavelength must be expressed in meters to keep units consistent.
2
Rearrange the electromagnetic wave speed formula c=fλc = f \lambda to solve for frequency ff.
f=cλ=3.0×108 m/s3.0×102 m=1.0×1010 Hzf = \frac{c}{\lambda} = \frac{3.0 \times 10^8\text{ m/s}}{3.0 \times 10^{-2}\text{ m}} = 1.0 \times 10^{10}\text{ Hz}
Frequency is the ratio of wave propagation speed to wavelength.
3
Convert the frequency from hertz to gigahertz.
f=1.0×1010 Hz109 Hz/GHz=10 GHzf = \frac{1.0 \times 10^{10}\text{ Hz}}{10^9\text{ Hz/GHz}} = 10\text{ GHz}
The question explicitly asks for the answer in gigahertz (GHz\text{GHz}).

Key Concept

Electromagnetic wave propagation equation (c=fλc = f \lambda) and unit metric prefixes.
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