Answer to Question 1
Single-phase power is more readily available than three phase power. Because of the popularity of single-phase power, a larger variety of equipment types and sizes are available.
Single-phase equipment is more readily available because it is often kept in stock at supply houses.
Answer to Question 2
Individual line current for a three-phase load is approximately 58 of a similarly sized single-phase load. Since wire is sized by current draw, reducing the line current also reduces the wire size and voltage drop. There is less power loss to transformers in using it.
Three phase motors are smaller, less expensive, more reliable, and more efficient than single phase. They do not require special capacitors to increase their starting torque.
Some three phase motors have an ability to correct the phase shift caused by some other inductive loads. Large commercial consumers of electric power are often faced with a surcharge that is applied to their base electrical rate when their power consumption is out of phase. Three phase motors can reduce or eliminate this surcharge by correcting the phase angle.
Answer to Question 3
Like poles repel each other and opposite poles attract.
Attack systems of pathogenic bacteria.
An overview of photosynthesis: cooperation of the light reactions and the Calvin cycle.
effect of light on plant
Acute Phase Proteins
Events in human fertilization. The light micrograph shows a fertilized human oocyte.