### How does an ice pyramid work?

Ice Spikes
If you go out one morning, just as the temperature has really started to drop, you might be forgiven for thinking that tiny aliens landed in your birdbath during the night. Birdbaths, as still pools of water that are left out in freezing conditions, are the most likely place to see inverted ice pyramids.

Regular ice spikes form because, at just the right temperature, the sides and top of a body of water - usually water in an ice cube tray - freeze first. As they freeze they expand, putting pressure on the water in the middle. If there is a tiny hole in the ice forming at the surface of the still-hardening cube, the liquid water is pushed upwards. The water pushed up through the hole forms a little frozen mound on the top of the ice cube. This little mound also has a hole in its center, through which more water is pushed, and the whole thing builds up into a spike.

Ice pyramids form through a variation on the process.The water doesn't freeze continuously, moving from the sides of the container to the middle. It freezes in what can best be described as "sheets." These sheets hang down vertically from the surface of the water. Sometimes they can be parallel to each other, as if someone were taking orderly slices from the water. Other times they can form at all angles to each other.

Inverted pyramids are formed when these sheets are at just the right angle to each other. Essentially, they form the shape, or the mold, for the pyramid under the water. In the meantime, the surface of the water freezes in roughly the shape of the pyramid base. At that point, the only way for the pyramid to go is up and out of the water. The only important part is that the "tip" of the pyramid doesn't freeze over, so more water can be forced into the pyramid "mold." As they ice sheets keep freezing and expanding, the pyramid is pushed up and up. Because the sheets are freezing, the underwater mold is getting smaller, the pyramid eventually tapers off to a point.

Eventually, the entire thing is frozen in place, waiting for people to be astonished by it the next morning. If you have a pond, a bird bath, or any small body of water that can freeze over, keep an eye out for an ice spike. Under the right conditions, the "spikes" can be pyramids, "cubes," or even vases.

### COMMON COLLECTOR CONFIGURATION OF A TRANSISTOR

COMMON COLLECTOR CONNECTION

In  this  configuration  the  input  is  applied  between the  base  and  the  collector and  the  output  is  taken  from  the  collector  and  the  emitter.  Here  the  collector  is common to both the input and the output circuits as shown in Fig.

Common Collector Transistor Circuit

In  common  collector  configuration  the  input  current  is  the  base current  IB  and  the output current is the emitter current IE. The ratio of change in emitter current to the  change in the base current is called current amplification factor.

It is represented by

COMMON COLLECTOR CIRCUIT

A test  circuit  for determining the  static characteristic  of an NPN transistor is shown in Fig. In this circuit the collector is common to both the input and the output circuits.   To   measure   the   base   and   the   emitter   currents,   milli   ammeters   are connected in series with the base and the emitter circuits. Voltmeters are connected   across the input an…