Question

Assume that a radio station is about $200$km away at your location and the station operates $972$ kHz. How long does it take for an electromagnetic signal to travel from the station to you and how many wave crests does it send out per second?

• A. $666\mu s$ and $9.72\times {10}^5$ crests per second
• B. $666\mu s$ and $972\times {10}^5$ crests per second
• C. $555\mu s$ and $97.2\times {10}^7$ crests per second
• D. $555\mu s$ and $9.72\times {10}^5$ crests per second
• E. $444\mu s$ and $9\times {10}^6$ crests per second

Answer 1

Answer: (A)

$666\mu s$ and $9.72\times {10}^5$ crests per second

The speed of radio waves is equal to electromagnetic wave speed i.e., $3\times {10}^{8}m/s$

Given, the distance of radio station, $s=200$km

$=200\times {10}^3$m

Time taken by radio wave to travel

$t=\frac{s}{c}=\frac{200\times {10}^3}{3\times {10}^8}$

$=666\times {10}^{-6}$

$=666\mu s$

The wave emitted send out per second $=972$kHz

$=972\times {10}^3$ Hz

$=9.72\times {10}^5$ crest per second.