Mark the correct statements

Options

A. If all the particle of a string are oscillating in same phase , the string is resonating in its fundamental tone
B. To observe interference , two sources of same frequency must be placed some distance apart from each other
C. To observe beats , two sources of same amplitude must be placed some distance apart from each other
D. None of the above

Answer

A, B

Explanation

In case of a stationary wave , all the particles lying between two consecutive nodes , oscillate in the same phase .
Since all the particles of given string are oscillating in the same phase , therefore , all the particles of the string lie between two consecutive nodes . Hence , the string is oscillating in the single loop . It means ,it is oscillating in its fundamental tone . Hence , option (a) is correct.
Interference is a phenomenon of obtaining constant intensity at a fixed position but the intensity varies with position of the point to point . Hence , to observe interference , two sources having same frequency must be placed some distance apart . Hence option (b) is correct.
Beats is a phenomenon of obtaining an intensity which varies with time . To obtain beats , two sources having different frequencies are required . Therefore , option ( c) is wrong.