# Problem 13-72 Double source interference - Part 2

An interference pattern using microwaves of wavelength $3.0\; cm$ is set up in a physics laboratory. (Microwaves are part of the electromagnetic spectrum; they travel at a speed of $3.0 \times 10^8\; m/s$ in air.) Two sources of in-phase waves are placed $18 \;cm$ apart and a receiver is located $4.8\; m$ away from the midpoint between the sources.
(a) What is the frequency of the microwaves? Express your answer in megahertz $(MHz)$ and gigahertz $(GHz)$.
(b) As the receiver is moved across the pattern parallel to an imaginary line joining the sources, what is the distance between adjacent maxima, between adjacent minima, and between a maximum and an adjacent minimum?

[Ans. (a) $10000\; MHz; 10\; GHz$  (b) $0.80\; m; 0.80\; m; 0.40\; m$ ]

Accumulated Solution

$v = f\lambda \; \text{or} \; f = v/\lambda = (3.0 \times 10^8\; m/s)/( 3.0 \times 10^{-2} \; m) = 1.0 \times 10^{10}\; Hz = 10\; GHz = 10000 \; MHz$

Let's make a drawing of the situation. Which is correct? (A)

(B)

(C)