Question

chapter 24 part 2

1. What is the frequency of a 17.7 m wavelength radio wave? Give your answe in MHz.

2. A 2.34 m diameter university communications
satellite dish receives TV signals that have a maximum electric
field strength (for one channel) of 7.51 μV/m. What is the power
received by the dish in 10^{-13} W?

3. A radio antenna can pick up wavelengths between 2.6
μm and 57.2 μm. How much of the frequency spectrum in (in
10^{13} Hz) does this cover?

4. Lasers can be constructed that produce an extremely
high intensity electromagnetic wave for a brief time—called pulsed
lasers. They are used to ignite nuclear fusion, for example. Such a
laser may produce an electromagnetic wave with a maximum electric
field strength of 2.32×10^{11} V / m for a time of
1.14 ns. What is the energy in kJ delivered on a 1.42
mm^{2} area?

Answer #1

1)given,

lambda = 17.7 m

We know that, v = f lambda

f = v/lambda = 3 x 10^8/17.7 = 1.7 x 10^7 Hz

Hence, f = 1.7 x 10^7 Hz = 17 MHz

2)Given,

E = 7.51 x 10^-6 V/m ; d = 2.34 m => r = 1.17 m

We know that

Erms = Em/sqrt(2) = 7.51 x 10^-6/1.414 = 5.31 x 10^-6 V/m

Erms = sqrt (I/ce0)

Erms^2 = I/ce0

I = Erms^2 c e0

I = (5.31 x 10^-6)^2 x 3 x 10^8 x 8.85 x 10^-12 = 7.49 x 10^-14 W/m^2

I = P/A

P = IA = 7.49 x 10^-14 x 4 x 3.14 x 1.17^2 = 1.29 x 10^-12 W

Hence, P = 1.29 x 10^-12 W = 12.9 x 10^-13 W

3)f1 = 3 x 10^8/(2.6 x 10^-6) = 1.15 x 10^14 Hz

f2 = 3 x 10^8/(57.2 x 10^-6) = 5.24 x 10^12 Hz

between: 0.524 x 10^13 Hz ; 11.5 x 10^13 Hz

A. 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. To what accuracy
in centimeters can the distance to the Moon be determined, if this
time can be measured to 0.11 ns?
B. Lasers can be constructed that produce an extremely high
intensity electromagnetic wave for a brief time—called pulsed
lasers. They are used to ignite nuclear fusion, for example. Such...

1. What is the maximum electric field strength in an
electromagnetic wave that has a maximum magnetic field strength of
7.4 × 10-4 T ?
Answer to the nearest whole number of kiloVolts per meter
(kV/m). No need to include the units.
2. A radio station utilizes frequencies between commercial AM
and FM. What is the frequency of a 46-m-wavelength channel?
Answer to 2 decimal place precision the number of MegaHertz
(MHz). No units required.
3. During normal beating, the...

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