A series of pulse of amplitude 0.15 m are sent down a string that is attached to a post at one end. The pulses are reflected at the post and travel back along the string without loss of amplitude. What is the amplitude at a point on the string where two pulses are crossing, (a) if the string is rigidly attached to the post? (b) if the end at which reflection occurs is free to slide up and down?
I have no clue srry
If rigid, it comes back opposite phase, so they cancel. If loose, it comes back in phase, so they add.
http://www.kettering.edu/~drussell/Demos/reflect/reflect.html
umm like i looked at it..i don't get what u mean it cancels out still..like are we supposed to use a formula?
No formula needed. Unless, you have difficulty understanding 1-1= cancel, and 1+1= twice amplidtude. :)
To understand why the pulses cancel out or add up, we can consider the principle of superposition.
(a) If the string is rigidly attached to the post, when a pulse reaches the post, it undergoes a phase change of 180 degrees (opposite phase) upon reflection. Therefore, when the reflected pulse meets another pulse at the same point, they are completely out of phase. This means the amplitudes of the two pulses will cancel each other out, resulting in an amplitude of zero at that point on the string.
(b) If the end at which reflection occurs is free to slide up and down, the pulse will undergo a phase change of 0 degrees (in phase) upon reflection. When the reflected pulse meets another pulse at the same point, they will be in phase. This means the amplitudes of the two pulses will add up, resulting in a doubled amplitude at that point on the string.
In conclusion:
(a) If the string is rigidly attached, the amplitude at the crossing point will be zero.
(b) If the end is free to slide, the amplitude at the crossing point will be twice the original amplitude.