Bell asked in Science & MathematicsPhysics · 2 months ago

Radio WPHY?

WPHY AM Radio transmits on a frequency of 760 kHz, omnidirectionally, with a power of 45 kW.

What is its wavelength?

 

Your friend who lives four times farther away from the station says she has problems listening to it. All other things being equal, her reception would be ...

 just the same as yours.

_ two times worse than yours.

_ four times worse than yours.

_ eight times worse than yours.

_ sixteen times worse than yours.

_ sixtyfour times worse than yours.

 

You live 31 km from the station. What is WPHY's intensity where you live?

A simple radio consists of an antenna as "voltage source" and an RCL circuit as tuner. The model shown has a fixed inductance and resistance, and a variable capacitor.

 The resonance frequency does not depend on the inductance.

 You tune to a higher frequency by increasing C.

 The resonance frequency does not depend on the resistance.

 The higher the resistance, the higher the resonance frequency.

If the inductance L is 1.1 mH and the resistance R is 20 Ω, what would the capacitance C have to be to tune in to WPHY?

4 Answers

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  • 2 months ago
    Favorite Answer

    λf = c

    λ = c/f = 3e9/760e3 = 3947 m

    strength goes down as the square of the distance, so 16

    intensity is a complicated topic. My guess is you want watts per square meter.

    45 kW, 31 km,  

    a sphere with radius of 31000 m has a surface area of 4πr² = 4π31000² = 1.21e10 m²

    so watts/m² = 45000/1.21e10 = 3.73e-6 or 3.73 µW/m²

    "The resonance frequency does not depend on the inductance" FALSE

    "You tune to a higher frequency by increasing C" FALSE

    "The resonance frequency does not depend on the resistance" TRUE

    "The higher the resistance, the higher the resonance frequency" FALSE

    If the inductance L is 1.1 mH and the resistance R is 20 Ω,

    f = 1/(2π√(LC)) = 760000

    2π√(LC) = 1/760000

    LC = (1/1530000π)²

    C = (1/0.0011) (1/1530000π)² = 3.9e-11 F or 39 pF

  • Zirp
    Lv 7
    2 months ago

    The wavelength would be 395 meter, not 3947

    We're talking mediumwave, not very long wave

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  • 2 months ago

    λf = c

    λ = c/f = 3e9/760e3 = 3947 m

    strength goes down as the square of the distance, so 16

    intensity is a complicated topic. My guess is you want watts per square meter.

    45 kW, 31 km,  

    • Bell2 months agoReport

      the speed of light is 3e8 not 9 but still thank you

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  • 2 months ago

    The wavelength λ of a sinusoidal waveform traveling at constant speed v is given by

    v = λf

    In this case, v is 'c', so we'll solve for Length

    λ = c/f  = 300,000m/s /(760,000cyles/s)

    λ = 0.395m or 395cm

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