Question

Harmonics problem. A square wave of frequency f contains harmonics (sine waves) at f, 3f, 5f, 7f, ... . Suppose a system responds to frequencies in the range 20-40 kHz but is insensitive outside of this range.
EXAMPLE:
Imagine applying a square wave with f = 30 kHz to this system. What is the shape of the response?
[Answer: a 30 kHz sine wave. ]
Imagine applying a square wave with f = 10 kHz to this system.

What is the shape of the response?
A. A 10 kHz sine wave
B. A combination of 20, 30 and 40 kHz sine waves
C. A 30 kHz sine wave
D. No response

Answer 1

Answer:

C.

Explanation:

• If the fundamental frequency of the square wave is 10 Khz, and contains harmonics at f, 3f, 5f, etc., it will have a component at 10 Khz, other at 30 Khz, and another one at 50 Khz.
• If the system responds to frequencies in the range between 20 Khz and 40 KHz only, the shape of the response will contain only a 30 Khz sine wave (3rd harmonic of 10 Khz).