24.3 The Electromagnetic Spectrum

The correct ordering from least to greatest wavelength is:

1. ELF, FM radio, microwaves, infrared, red, green, ultraviolet, x-ray, gamma ray
2. ELF, FM radio, microwaves, infrared, green, red, ultraviolet, x-ray, gamma ray
3. gamma ray, x-ray, ultraviolet, red, green, infrared, microwaves, FM radio, ELF
4. gamma ray, x-ray, ultraviolet, green, red, infrared, microwaves, FM radio, ELF

(a) Two microwave frequencies are authorized for use in microwave ovens: 900 and 2560 MHz. Calculate the wavelength of each. (b) Which frequency would produce smaller hot spots in foods due to interference effects?

A radio station utilizes frequencies between commercial AM and FM. What is the frequency of a 11.12-m-wavelength channel?

Combing your hair leads to excess electrons on the comb. How fast would you have to move the comb up and down to produce red light?

Approximately what is the smallest detail observable with a microscope that uses ultraviolet light of frequency $1 . \text{20} \times \text{10}^{\text{15}} \text{ Hz}$?

Some radar systems detect the size and shape of objects such as aircraft and geological terrain. Approximately what is the smallest observable detail utilizing 500-MHz radar?

If you wish to detect details of the size of atoms (about $1 \times \text{10}^{- \text{10}} \text{ m}$) with electromagnetic radiation, it must have a wavelength of about this size. (a) What is its frequency? (b) What type of electromagnetic radiation might this be?

A certain 50.0-Hz AC power line radiates an electromagnetic wave having a maximum electric field strength of 13.0 kV/m. (a) What is the wavelength of this very low frequency electromagnetic wave? (b) What is its maximum magnetic field strength?

(a) The ideal size (most efficient) for a broadcast antenna with one end on the ground is one-fourth the wavelength ($\lambda / 4$) of the electromagnetic radiation being sent out. If a new radio station has such an antenna that is 50.0 m high, what frequency does it broadcast most efficiently? Is this in the AM or FM band? (b) Discuss the analogy of the fundamental resonant mode of an air column closed at on…

(a) What is the frequency of the 193-nm ultraviolet radiation used in laser eye surgery? (b) Assuming the accuracy with which this EM radiation can ablate the cornea is directly proportional to wavelength, how much more accurate can this UV be than the shortest visible wavelength of light?

Conversations with astronauts on lunar walks had an echo that was used to estimate the distance to the Moon. The sound spoken by the person on Earth was transformed into a radio signal sent to the Moon, and transformed back into sound on a speaker inside the astronaut’s space suit. This sound was picked up by the microphone in the space suit (intended for the astronaut’s voice) and sent back to Ea…

Radar is used to determine distances to various objects by measuring the round-trip time for an echo from the object. (a) How far away is the planet Venus if the echo time is 1000 s? (b) What is the echo time for a car 75.0 m from a Highway Police radar unit? (c) How accurately (in nanoseconds) must you be able to measure the echo time to an airplane 12.0 km away to determine its distance within 1…

(a) Calculate the rate in watts at which heat transfer through radiation occurs (almost entirely in the infrared) from $1 . 0 \text{ m}^{2}$ of the Earth’s surface at night. Assume the emissivity is 0.90, the temperature of the Earth is $\text{15}º \text{C}$, and that of outer space is 2.7 K. (b) Compare the intensity of this radiation with that coming to the Earth from the Sun during the day, which averages about $\text{800} \text{ W}/\text{m}^{2}$, only half of whic…