Physics Form 5: Chapter 4 - P-N Junction of Semiconductor

A small quantity of electrons on the n-side of the junction are attracted by the "holes" in the p-side. They drift across the junction, and fill available holes. This causes a region across the junction to be depleted in carriers of current (that is, electrons and "holes"). This region is called the DEPLETION LAYER, because it has been depleted in majority carriers. The depletion zone is a few micrometers thick, and, since it has no majority carriers, acts as an insulating barrier.

It is important to realise that when electrons moves from the n-side of the junction to the p-side, the n-side becomes positively charged (since neutral atoms have lost electrons), while the p-side of the junction now becomes negatively charged (since neutral atoms have now acquired negatively charged electrons). A potential difference now exists across the junction. This potential difference is about 0.6 V for silicon, and about 0.2 V for germanium. This is called the BARRIER POTENTIAL.

Why I decided to stop teaching after 19 years - Bernard Khoo

How different is education today, I was asked, compared with education when I was an educator?

Well, if I lasted 19 years as a teacher, it must have been a tolerable profession. Key operative word is “tolerable” despite the fact that in the mid-1960s, we teachers throughout the country went on strike to seek better remuneration.

When I opted to come back from Singapore after her separation from Malaysia to continue to make teaching my career my late meter-reader father warned me about the responsibility the job entailed.

“I already got you a job at LLN (now Tenaga) through Raja Zainal (then CEO)," he said.

He continued: "As a teacher you are responsible for ALL students in your class. They spend more hours with you than with their parents. If one goes astray, you have failed as the teacher!”

He sure threw a bucket of cold water on my vocation. I stuck to teaching, emboldened by the challenge  that I had, to emulate my former teachers, the men who nurtured me for this noble profession. I spent 10 years in a Sentul school after which I was assigned to another to stem the drug indiscipline in that school.

So, why did I throw all this away, besides the loss of pension and gratuity after 19 years?

After 1970, all schools were converted into government or government assisted schools and the Bahasa Kebangsaan (Bahasa Malaysia) would be the medium of instruction.

Three months of inservice course to learn Bahasa was deemed sufficient for one to be proficient in this new medium of instruction. I plodded on, even on occasions when I was just three pages ahead of my students.

That was the policy and I tried to do my best. And then I witnessed the insidious part race and religion snaked into the profession.

When handball was introduced in the sports curriculum I purchased the necessary. I was called into the office to justify why I purchased handball made from pig skin. I produced the ball that had the offending word “pigment” imprinted on it.

When the omnipotent words - race, religion and quota - took precedence over merit that resulted in shameless polarisation that then divided our student body, I wanted no part of this system and forfeited  one month’s salary in lieu of immediate resignation.

They say that once a teacher, always a teacher. I continued teaching as an internationally certified corporate trainer and coach, where race and religion could not find a foothold in multi-national corporations but lost a lucrative contract with a statutory body when it was revealed that I was an anti-establishment blogger.

So what’s new with this latest episode of the dressing room canteen?

The politicising of race and religion will continue unabated so we former teachers just pray that one day this beautiful country and its people can live together in harmony and undivided by people who use race and religion to control. - July 25, 2013.

* Bernard Khoo is a retired teacher who reads The Malaysian Insider.

Physics Form 5: Chapter 4 - The Doping of Semiconductor

An extrinsic semiconductor is an improved intrinsic semiconductor with a small amount of impurities added by a process, known as doping, which alters the electrical properties of the semiconductor. Doping process can improve semiconductor's electrical conductivity. Doping process produces two groups of semiconductor: the negative charge conductor (n-type) and the positive charge conductor (p-type). 

N-type semiconductor

Doped by pentavalent impurities which has 5 valence electrons to produce n-type semiconductors by contributing extra electrons. The addition such as antimony, arsenic or phosphorus contributes free electrons, greatly increasing the conductivity of the intrinsic semiconductor. 

This allows four of the five electrons to bond with its neighbouring silicon atoms leaving one "free electron" to move about when an electrical voltage is applied (electron flow).

P-type semiconductor

Doped by trivalent impurities which has 3 valence electrons to produce p-type semiconductors by producing a "HOLE". The addition such as boron, aluminium or gallium to an intrinsic semiconductor creates deficiencies of valence electrons, called "hole".

As there is a hole an adjoining free electron is attracted to it and will try to move into the hole to fill it. However, the electron filling the hole leaves another hole behind it as it moves. This in turn attracts another electron which in turn creates another hole behind, and so forth giving the appearance that the holes are moving as a positive charge through the crystal structure


Conclusion

Again and again.......How many times?

How am I going to encourage my ex SPM students to study Form SIX? Please answer me, Mr. Minister of Education. Please don't give any lame excuses such as technical error. Shame on you MOE!

Chai Yee Lin, a straight-A scorer in the STPM, had been hoping to further her studies in medicine or dentistry in a local public university of her choice.The teenager was sorely disappointed when she found out that she was only offered a place in Universiti Malaysia Kelantan to do veterinary science.

"Yes, I did state veterinary science as one of the secondary courses in the admission form, but I was confident that with my good results, I could get medicine or dentistry," she said.

Adding salt to the wound, Chai, who was hoping to support her family, later learnt that  a friend with lower scores was offered dentistry at Universiti Sains Malaysia.

The MCA and MIC have voiced out the grievances of students, claiming that fewer Chinese and Indian students had secured places in universities this year.

The Straits TImes reported that university entry has been a long-standing issue in the country, where racial quotas, favouring Malays and other bumiputeras, were used to determine entry into public higher-learning institutions.

The quotas were removed in 2002, and entry is now up to the discretion of higher education authorities.

It was reported that MCA education bureau chairman Wee Ka Siong has refused to accept the explanation from the Education Ministry that the candidates were denied entry into universities due to a technical glitch.

"I cannot accept this silly explanation. It is grossly unfair to the students," he said in Wisma MCA after meeting 22 students and their families on Tuesday.

MIC national youth council member G Kalaicelvan said the party had also received several complaints from top Indian students who had failed to gain admission to the course of their choice.

"Most want to do medicine and their STPM results meet the requirement but somehow they do not get a place in the public universities," The Straits Times quoted him as saying.

More than 18,000 students had failed to get places in public institutions of higher learning although they had met the requirements, said Deputy Education Minister P. Kamalanathan, urging them to appeal.

Prime Minister Datuk Seri Najib Razak, in acknowledging the issue, had tweeted, urging the disappointed students not to give up.

"I know some were disappointed to not get a place at uni, but don't give up. Will discuss at Cabinet this week how to best help these students," he said. - AFP, July 18, 2013.

Physics Form 5: Chapter 4 - Semiconductor

Semiconductor is a material where its electrical conductivity lie between conductors and insulators. In semiconductors, thermal energy is enough to cause a small number of electrons to escape from the valence band of atom to the higher energy of conduction band, in which they are relatively free to move. The resulting gaps in the valence band are called holes.

Usually, semiconductors are made from semi-metal or called metalloid from the Periodic Table. 

Silicon is the most preferred material for semiconductors because:

• ease of availability
• low cost of processing 
• higher temperature range
• high resistivity than other counterparts 
• low leakage current

Semiconductors are widely use in making diode, transistor and integrated circuit

Women make up 68% of Public Universities Intake

Women make up 68.02 per cent (28,280) of 41,573 applicants who gained admission to public institutions of higher learning (IPTAs) for the first degree in the 2013/2014 academic session.
They were chosen from 68,702 applicants, with 24,489 or 58.9 per cent of them from the science stream and 17,084 (41.1 per cent) from the arts stream, said Higher Education Department director-general Prof Datuk Morshidi Sirat.

He said 49 of the successful applicants were Orang Asli; 68 were physically challenged; and 1,515 were national and international athletes.

Morshidi said the IPTAs will issue formal offer letters to successful candidates beginning tomorrow.
He said 74.3 per cent or 30,903 of the successful candidates were Bumiputera, 19 per cent or 7,913, Chinese; 4.4 per cent or 1,824, Indians; and 2.3 per cent or 933 were from other ethnic groups.
Morshidi said 5,765 candidates were offered competitive courses, namely medicine (699), dentistry (119), pharmacy (260), law (385), chemical engineering (953), mechanical engineering (1,304), electrical and electronic engineering (1,122) and accounting (923).

The admission is based on the order of merit and selection of programmes in the universities applied for, he said, adding: "If the merit of a candidate is not so high and he applied for a competitive programme, it is unlikely that he [will be] offered the programme."
The status of applications can be checked at upu, jpt.utm, jpt.uum, jpt.unimas, jpt.ums from today, or by contacting the hotline 03-8870 6767, helpline 03-8870 6777, general line 03-8870 6755/6766 or by texting UPU RESULT (IC no) to 15888.

"Successful candidates must confirm acceptance within 10 days of the offer, on or before July 21. Letters of offer and confirmation can be printed from the IPTA website," he said.
Candidates can also go to the Student Admission Management Division, Higher Education Department in Presint 5, to check the status of their applications from today until July 21.
Unsuccessful candidates can file an appeal online within 10 days through e-Rayuan at upu.mohe.gov.my starting today, until midnight on July 21.
Morshidi said appeals are subject to availability of places and would be deemed unsuccessful if no reply came from the IPTA concerned by Sept 30.
Registration of the new intake will be held on Sept 1 and 2, he added. - Bernama, July 11, 2013.

 

Chemistry Form 4 - Chapter 7: Examples of Acid - Base Indicator

Acid - base indicator is used in titration method to determine the end point of neutralisation process. The acid-base indicator basically is some weak organic acid or base dye that changes colours at definite pH values.

For further information, click below

Please Don't Intimidate Teacher......

Jangan ugut kami untuk undi kamu, kata NUTP

Guru-guru tidak seharusnya “diintimidasi atau diperas ugut" untuk mengundi mana-mana parti politik kata Kesatuan Perkhidmatan Perguruan Kebangsaan (NUTP) mengingatkan parti-parti politik.

Presidennya Hashim Adnan mengatakan ini sebagai respon kepada Menteri Pendidikan II Datuk Seri Idris Jusoh yang menggesa guru-guru untuk mengundi Barisan Nasional (BN) dalam pilihan raya kecil (PRK) akan datang sebagai melahirkan rasa terima kasih kepada kerajaan.

“Guru-guru boleh mengundi sesiapa yang mereka mahu. Saya tidak akan menuntut atau memaksa guru-guru untuk mengundi Barisan Nasional,” kata Hashim kepada The Malaysian Insider hari ini.

Beliau menambah: “Jika mereka gembira dengan apa yang diterima dan jika mahu mereka (BN) terus berkhidmat kerana telah melaksanakan tanggungjawab dengan baik, mereka boleh mengundi BN.

“Semuanya terpulang kepada mereka. Mereka tidak seharusnya diintimidasi atau diperas ugut.”

Hashim mengatakan kerajaan tidak seharusnya mengambil mudah terhadap guru-guru.

“Apabila anda terlalu lama berkuasa, adalah normal untuk membuat gesaan seperti itu... sudah menjadi kebiasaan orang dijawatan seperti itu akan lakukan,” tambah beliau, akan tetapi memberi amaran kedua-dua pihak agar tidak membuli guru-guru untuk mengundi mereka.

Semalam Idris berkata undi kepada BN adalah bagi melahirkan rasa terima kasih kepada kerajaan yang banyak memperjuangkan kebajikan mereka.

"Tidak ada sebab guru membiarkan kerajaan bersendirian dan kini sampai masanya mereka membantu kerajaan untuk memastikan BN mengekalkan kerusi di Kuala Besut sebagai ucapan terima kasih mereka kepada kerajaan," katanya kepada pemberita semasa beramah mesra dengan penduduk Kampung Kemunting dekat Kuala Besut semalam.

Gesaan Idris mengingatkan kembali mengenai pilihan raya kecil Tenang dahulu apabila pengarah pendidikan negeri Markom Giran dikatakan menyalahgunakan kuasa apabila mengarah guru-guru untuk memastikan kemenangan BN.

Pengarah Pilihan Raya PAS bagi kerusi Dewan Undangan Negeri (DUN) Tenang Dzulkefly Ahmad membuat laporan terhadap Makom kerana melawat sekolah di Labis dan Tenang menyuruh guru-guru memastikan kemenangan BN.

Dzulkefly turut menyerahkan klip video empat minit yang dimuat naik ke Youtube menunjukkan Markom memberikan ucapan kepada guru-guru. – 7 Julai, 2013.