FOLLOW US ON TWITTER
SHARE THIS PAGE ON FACEBOOK, TWITTER, WHATSAPP ... USING THE BUTTONS ON THE LEFT


YOUR PARTICIPATION FOR THE GROWTH OF PHYSICS REFERENCE BLOG

Monday, May 1, 2017

A uniform string is held between a fixed point P and a variable-frequency oscillator, as shown in Fig. 5.1.




Question 1
A uniform string is held between a fixed point P and a variable-frequency oscillator, as shown in Fig. 5.1.

Fig. 5.1
The distance between point P and the oscillator is L.
The frequency of the oscillator is adjusted so that the stationary wave shown in Fig. 5.1 is formed.
Points X and Y are two points on the string.
Point X is a distance 1/8 L from the end of the string attached to the oscillator. It vibrates with frequency f and amplitude A.
Point Y is a distance 1/8 L from the end P of the string.

(a) For the vibrations of point Y, state
(i) the frequency (in terms of f ), [1]
(ii) the amplitude (in terms of A). [1]

(b) State the phase difference between the vibrations of point X and point Y. [1]

(c) (i) State, in terms of f and L, the speed of the wave on the string. [1]

(ii) The wave on the string is a stationary wave.
Explain, by reference to the formation of a stationary wave, what is meant by the
speed stated in (i). [3]





Reference: Past Exam Paper – November 2009 Paper 22 Q5





Solution 1:
(a)
(i) f                                          [B1]

(ii) A                                        [B1]
{Amplitude means maximum displacement.}


(b) 180o           or Ï€ rad            (unit necessary)                       [B1]
{When talking about the phase of a point, we need to consider its displacement and the direction of motion/vibration.
Phase difference between 2 points means the difference in phase about the 2 points.
Point X and Y are at the same displacement (one is +ve and the other -ve). However, they moving in opposite direction. So, they are out of phase (phase difference = 180°).}

[For more explanation on Phase difference, see solution 318 at http://physics-ref.blogspot.com/2015/01/physics-9702-doubts-help-page-55.html]


(c) (i) Speed of wave = f x L                                                  [B1]

(ii)
The wave is reflected at the end / at P.                       [B1]
EITHER The incident and reflected waves interfere OR the two waves travelling in opposite directions interfere.                                              [M1]
The speed is the speed of incident or reflected wave / one of these waves.  [A1]

1 comment:

If it's a past exam question, do not include links to the paper. Only the reference.
Comments will only be published after moderation

Currently Viewing: Physics Reference | A uniform string is held between a fixed point P and a variable-frequency oscillator, as shown in Fig. 5.1.