<< Chapter < Page Chapter >> Page >

If you wish to detect details of the size of atoms (about 1 × 10 10 m size 12{1´"10" rSup { size 8{-"10"} } " 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) f = c λ = 3 . 00 × 10 8 m/s 1 × 10 - 10 m = 3 × 10 18 Hz size 12{f= { {c} over {λ} } = { {3 "." "00"´"10" rSup { size 8{8} } " m/s"} over {1´"10" rSup { size 8{ +- "10"} } " m"} } = {underline {3´"10" rSup { size 8{"18"} } " Hz"}} } {}

(b) X-rays

Got questions? Get instant answers now!

If the Sun suddenly turned off, we would not know it until its light stopped coming. How long would that be, given that the Sun is 1 . 50 × 10 11 m size 12{1 "." "50"´"10" rSup { size 8{"11"} } " m"} {} away?

Got questions? Get instant answers now!

Distances in space are often quoted in units of light years, the distance light travels in one year. (a) How many meters is a light year? (b) How many meters is it to Andromeda, the nearest large galaxy, given that it is 2 . 00 × 10 6 size 12{2 "." "00"´"10" rSup { size 8{6} } } {} light years away? (c) The most distant galaxy yet discovered is 12 . 0 × 10 9 size 12{"12" "." 0´"10" rSup { size 8{9} } } {} light years away. How far is this in meters?

Got questions? Get instant answers now!

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) 6.00 × 10 6 m size 12{5 "." "00" times "10" rSup { size 8{6} } " m"} {}

(b) 4 . 33 × 10 5 T size 12{4 "." "33" times "10" rSup { size 8{ - 5} } " T"} {}

Got questions? Get instant answers now!

During normal beating, the heart creates a maximum 4.00-mV potential across 0.300 m of a person’s chest, creating a 1.00-Hz electromagnetic wave. (a) What is the maximum electric field strength created? (b) What is the corresponding maximum magnetic field strength in the electromagnetic wave? (c) What is the wavelength of the electromagnetic wave?

Got questions? Get instant answers now!

(a) The ideal size (most efficient) for a broadcast antenna with one end on the ground is one-fourth the wavelength ( λ / 4 size 12{λ/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 one end to the resonance of currents on an antenna that is one-fourth their wavelength.

(a) 1.50 × 10 6 Hz, AM band
(b) The resonance of currents on an antenna that is 1/4 their wavelength is analogous to the fundamental resonant mode of an air column closed at one end, since the tube also has a length equal to 1/4 the wavelength of the fundamental oscillation.

Got questions? Get instant answers now!

(a) What is the wavelength of 100-MHz radio waves used in an MRI unit? (b) If the frequencies are swept over a ± 1 . 00 size 12{ +- 1 "." "00"%} {} range centered on 100 MHz, what is the range of wavelengths broadcast?

Got questions? Get instant answers now!

(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?

(a) 1 . 55 × 10 15 Hz size 12{1 "." "55" times "10" rSup { size 8{"15"} } " Hz"} {}

(b) The shortest wavelength of visible light is 380 nm, so that

λ visible λ UV = 380 nm 193 nm = 1 . 97 . alignl { stack { size 12{ { {λ rSub { size 8{"visible"} } } over {λ rSub { size 8{"UV"} } } } } {} #= { {"380 nm"} over {"193 nm"} } {} # =1 "." "97" "." {}} } {}

In other words, the UV radiation is 97% more accurate than the shortest wavelength of visible light, or almost twice as accurate!

Got questions? Get instant answers now!

TV-reception antennas for VHF are constructed with cross wires supported at their centers, as shown in [link] . The ideal length for the cross wires is one-half the wavelength to be received, with the more expensive antennas having one for each channel. Suppose you measure the lengths of the wires for particular channels and find them to be 1.94 and 0.753 m long, respectively. What are the frequencies for these channels?

The picture of a television reception antenna mounted on the roof of a house. An enlarged image of the antenna is also shown. The antenna has a long horizontal rod having smaller cross wires of decreasing length from left to right. The cross wires are numbered from two to thirteen.
A television reception antenna has cross wires of various lengths to most efficiently receive different wavelengths.
Got questions? Get instant answers now!

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 Earth as a radio echo of sorts. If the round-trip time was 2.60 s, what was the approximate distance to the Moon, neglecting any delays in the electronics?

3 . 90 × 10 8 m size 12{3 "." "90" times "10" rSup { size 8{8} } " m"} {}

Got questions? Get instant answers now!

Lunar astronauts placed a reflector on the Moon’s surface, off which a laser beam is periodically reflected. The distance to the Moon is calculated from the round-trip time. (a) To what accuracy in meters can the distance to the Moon be determined, if this time can be measured to 0.100 ns? (b) What percent accuracy is this, given the average distance to the Moon is 3 . 84 × 10 8 m size 12{3 "." "84"´"10" rSup { size 8{8} } " m"} {} ?

Got questions? Get instant answers now!

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 10.0 m?

(a) 1 . 50 × 10 11 m size 12{1 "." "50" times "10" rSup { size 8{"11"} } " m"} {}

(b) 0 . 500 μ s size 12{0 "." "500 "ms} {}

(c) 66.7 ns

Got questions? Get instant answers now!

Integrated Concepts

(a) Calculate the ratio of the highest to lowest frequencies of electromagnetic waves the eye can see, given the wavelength range of visible light is from 380 to 760 nm. (b) Compare this with the ratio of highest to lowest frequencies the ear can hear.

Got questions? Get instant answers now!

Integrated Concepts

(a) Calculate the rate in watts at which heat transfer through radiation occurs (almost entirely in the infrared) from 1 . 0 m 2 size 12{1 "." 0" m" rSup { size 8{2} } } {} of the Earth’s surface at night. Assume the emissivity is 0.90, the temperature of the Earth is 15º C size 12{"15"°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 800 W/m 2 size 12{"800"" W/m" rSup { size 8{2} } } {} , only half of which is absorbed. (c) What is the maximum magnetic field strength in the outgoing radiation, assuming it is a continuous wave?

(a) 3 . 5 × 10 2 W/m 2 size 12{-3 "." 5´"10" rSup { size 8{2} } " W/m" rSup { size 8{2} } } {}

(b) 88%

(c) 1 . 7 μ T size 12{1 "." 7 mT} {}

Got questions? Get instant answers now!

Questions & Answers

What is meant by dielectric charge?
It's Reply
what happens to the size of charge if the dielectric is changed?
Brhanu Reply
omega= omega not +alpha t derivation
Provakar Reply
u have to derivate it respected to time ...and as w is the angular velocity uu will relace it with "thita × time""
Abrar
do to be peaceful with any body
Brhanu Reply
the angle subtended at the center of sphere of radius r in steradian is equal to 4 pi how?
Saeed Reply
if for diatonic gas Cv =5R/2 then gamma is equal to 7/5 how?
Saeed
define variable velocity
Ali Reply
displacement in easy way.
Mubashir Reply
binding energy per nucleon
Poonam Reply
why God created humanity
Manuel Reply
Because HE needs someone to dominate the earth (Gen. 1:26)
Olorunfemi
why god made humenity
Ali
Is the object in a conductor or an insulator? Justify your answer. whats the answer to this question? pls need help figure is given above
Jun Reply
ok we can say body is electrically neutral ...conductor this quality is given to most metalls who have free electron in orbital d ...but human doesn't have ...so we re made from insulator or dielectric material ... furthermore, the menirals in our body like k, Fe , cu , zn
Abrar
when we face electric shock these elements work as a conductor that's why we got this shock
Abrar
how do i calculate the pressure on the base of a deposit if the deposit is moving with a linear aceleration
ximena Reply
why electromagnetic induction is not used in room heater ?
Gopi Reply
room?
Abrar
What is position?
Amoah Reply
What is law of gravition
sushil Reply
what is magnetism
Sandeep Reply

Get the best College physics for ap... course in your pocket!





Source:  OpenStax, College physics for ap® courses. OpenStax CNX. Nov 04, 2016 Download for free at https://legacy.cnx.org/content/col11844/1.14
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'College physics for ap® courses' conversation and receive update notifications?

Ask