Question

Which of the following statement is/are true in case of waves ?

• A. Transverse vibrations are set on the string of a guitar.
• B. As compared to light, a sound wave produced on the moon will take a time about ${10}^6$ times longer to reach the earth.
• C. A sound note of wavelength 1 cm in air cannot be heard by a man.
• D. Sound travels faster in water than in air.

Answer 1

Answer: (A), (C), (D)

The correct options are
A Transverse vibrations are set on the string of a guitar.
C A sound note of wavelength 1 cm in air cannot be heard by a man.
D Sound travels faster in water than in air.

(A) When a guitar string is struck , string is disturbed and the medium (string) particles vibrate perpendicular to the direction of motion disturbance , therefore transverse vibrations are set on the guitar string . -True

(B) Sound wave are longitudinal mechanical waves , which require a medium to travel as there is no medium on moon , so they cannot travel there and can't reach to earth . Whereas light waves ,being electromagnetic waves can travel to earth . -False

(C) If wavelength $\lambda =1cm=0.001m$ and $v=332m/s$ ,

then frequency $f=v/\lambda =332/0.001=332000Hz$ ,

that is an ultrasonic frequency which cannot be heard by a man . -True

(D) Sound travels faster in liquid than gases due to higher elasticity of liquids , therefore sound travels faster in water than in air . -True