# Frequency of microwaves

1. May 30, 2006

### Amith2006

Sir,
1)Microwaves are directed normally at a plane metallic reflector. A detector moving along the normal to the reflector travels 15 cm from the first to the 11th successive of minimum intensity. What is the frequency of the microwave?(velocity of microwaves = 3 x 10^8 m/sec)
I solved it in the following way:
The incident and the reflected microwaves superimpose to produce standing waves. The distance between the first and the 11th minimum is given that it is 15 cm.
Therefore,
0.15 = 10 x (lambda/2)
Lambda = 0.03 meters
Frequency = (3 x 10^8)/ 0.03
= 10^10 Hz
Is it right?
2)Two waves of same frequency travel in opposite directions in a medium with amplitudes 3 units and 2 units respectively. What is the ratio of the amplitudes at an antinode and a node in the stationary wave?
I think it is infinity because at the antinode it has maximum amplitude and at the node it is zero. Is it right?

2. May 30, 2006

### Hootenanny

Staff Emeritus
This looks good to me. Just a small point however, using standard scientific notation it is better to quote the answer as 1x1010 Hz. However, both are correct.

Are you sure about that? The formal definition of a node is "a point of minimum displacement.", this need not to be zero. The important thing to note is the respective amplitudes, try sketching the two waves in anti-phase on the same graph.

~H