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.
Answer:
RoHS applies to the following substances for electronic equipment and electrical appliances: lead, mercury, cadmium, hexavalent chromium, PBB (polybrominated biphenyls), and some PBDEs (polybrominated diphenyl ethers).
<span>The correct answer for the question is Non-disjunction. Non-disjunction occurs in cell division when chromosomes do not divide properly. It can occur during mitosis, meiosis I and meiosis II. In mitosis it occurs when sister chromatids fails to separate in Anaphase. The result is that one cell receives both chromatids, while the other receives neither. Each daughter cell then has an abnormal number of chromosomes when mitosis is complete; one cell has an extra chromosome, while the other is missing one. In anaphase of meiosis I, it happens when a pair of homologous chromosomes does not separate. In meiosis II, it happens when a pair of sister chromatids fails to separate properly during anaphase of meiosis II, one daughter cell will have an extra chromosome and one daughter cell will be missing a chromosome.</span>
The cytoplasm and the nucleus together are known as the protoplasm, the living matter of the cell.
