What points of teh stretched string betweeen two fixed points must be plucked and touched to excite its first overtone?

What is the phase difference between two points on a wavefront?

What is the potential difference between two points in the electric field? Name its SI unit.

What is meant by saying that the potential difference between two points is 1 V?

Show that the line integral of electric field ntensity between any two points depends only on the position of these points and its independent of the path followed between these points.

In many experimental set-ups, the source and screen are fixed at a distance say D and the lens is movable.Show that there are two positions for the lens,for which an image is formed on the sceen.Find the distance between these points and the ratio of the image sizes for these two points.

The wave pattern on a stretched string is shown in the figure. Interpret what kind of wave this is and find its wavelength?