Fuel cells can make an electricity from a simple electrochemical
reaction in which oxygen and hydrogen combine to form water. There are several
different types of fuel cell but they are all based around a central design
which consists of two electrodes, a negative anode and a positive cathode.
These are separated by a solid or liquid electrolyte that carries electrically
charged particles between the two electrodes. A catalyst, such as platinum, is
often used to speed up the reactions at the electrodes. Fuel cells are
classified according to the nature of the electrolyte. Every type needs
particular materials and fuels and is suitable for any applications. The
article below uses the proton exchange membrane fuel cell to illustrate the
science and technology behind the fuel cell concept but the characteristics and
applications of the other main designs are also discussed. Proton Exchange Membrane Fuel Cells (PEMFC)
The hydrogen ions permeate across the electrolyte to the
cathode, while the electrons flow through an external circuit and provide
power. Oxygen, in the form of air, is supplied to the cathode and this combines
with the electrons and the hydrogen ions to produce water. These reactions at
the electrodes are as follows:
Anode: 2H24H+ + 4e-
Cathode: O2 + 4H+ + 4e- 2H2O
Overall: 2H2 + O22H2O + energy
PEM cells operate at a temperature of around 80°C. At this
low temperature the electrochemical reactions would normally occur very slowly
so they are catalysed by a thin layer of platinum on each electrode.
The longest phase of mitosis is prophase. Because the nuclear membrane disappears, Nucleolus disintegrates, and the DNA condensed to form chromosomes (each chromosome is composed of sister chromatids attached around centromere.)
B) Meiosis-"a type of cell division that results in four daughter cells each with half the number of chromosomes of the parent cell, as in the production of gametes and plant spores." taken from google
Answer:
<u>Liquefaction</u> refers to the tendency of a foundation material (such as soil) that is water-logged to lose its internal cohesion and mechanically fail to provide support during earthquake shaking.
Explanation:
Liquefaction occurs when an unbound material (usually sand), which is saturated in water, loses its resistance to shear due to intense and rapid vibration (earthquake), which breaks its granular structure by reducing its inter-granular pressure and flow like a liquid because of an increase in pressure.
Liquefaction usually manifests itself in loose, saturated and non-cohesive soils, formed by young deposits of sands and sediments of similar particle sizes. If the soil is dense there will be less chances of liquefaction. Older deposits, in general, are more dense and cohesive. At higher density, more interstitial pressure is needed for liquefaction to occur.
