Most optical elements (mirrors, lenses) can be characterized by basically one quantity: their focal length. To understand focal length, we need to know something about the focal point. In the image above, note how the light rays, after they pass through the lens, converge on a single point. Below is a schematic drawing of the above situation. The single point to which the light rays are converging is called the focal point.
Tsk is a sound made by quickly releasing the tongue from the top of the mouth to express disapproval or criticism. An example of tsk is the sound a mother would make while shaking her finger at a child who's done something wrong. (a sound) used to express disapproval, genuine or mock sympathy, etc.: a click, or sucking sound, made by touching the tongue to the hard palate and rapidly withdrawing it.
Definition of pK. pK is a negative logarithmic scale of any rate constant. One of the most important examples of pK is pK a, the scale of relative acid strength. pK a is the negative log of the acid dissociation constant (pKa=-log([A-][H+]/[HA])).The Henderson-Hasselbalch equation relates pK a and pH to the relative concentrations of an acid and conjugate base in solution (pH=pKa+log([A-]/[HA])) .ne of the most important examples of pK is pK a, the scale of relative acid strength.