Two 1.0-MHz radio antennae emitting in-phase are separated by 600m along a north

Question

Two 1.0-MHz radio antennae emitting in-phase are separated by 600m along

a north-south line. A radio placed 20km east is equidistant from both

transmitting antennae and picks up a strong (maximum) signal. How far

north should that receiver be moved if it is again to detect a signal as strong?

[Remember radio waves are light, too!! Those antennae are where your two

waves are coming from, like two slits. The receiver is like a screen, and the

strong signal is a bright fringe. The question is about where the m=1 bright

fringe is.] pls answer that

Explanation / Answer

f = 10^6 Hz

lamda = c/f = 3*10^8/10^6 = 300 m

for constructive inerference,

ym = m*lamda*L/d

for m = 1

y1 = lamda*L/d

here, L = 20 km = 20000 m

d = 600 m


so, y = 300*20000/600

= 10000 m

= 10 km

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