Problem: A P-N junction can convert absorbed light energy into a proportional electric current. The same process is reversed here (i.e. the P-N junction emits light when electrical energy is applied to it). This phenomenon is generally called electroluminescence, which can be defined as the emission of light from a semi-conductor under the influence of an electric field. The charge carriers recombine in a forward-biased P-N junction as the electrons cross from the N-region and recombine with the holes existing in the P-region. Free electrons are in the conduction band of energy levels, while holes are in the valence energy band. Thus the energy level of the holes will be lesser than the energy levels of the electrons. Some portion of the energy must be dissipated in order to recombine the electrons and the holes. This energy is emitted in the form of heat and light.
What is the phenomenon where a P-N junction emits light when a non-electrical current is applied to it?
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Answer: unanswerable

Problem: As a result of modernisation efforts over the years, Egypt's healthcare system has made great strides forward. Access to healthcare in both urban and rural areas greatly improved and immunisation programs are now able to cover 98% of the population. Life expectancy increased from 44.8 years during the 1960s to 72.12 years in 2009. There was a noticeable decline of the infant mortality rate (during the 1970s to the 1980s the infant mortality rate was 101-132/1000 live births, in 2000 the rate was 50-60/1000, and in 2008 it was 28-30/1000).
What was life expectancy in 1960s?
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Answer: 44.8 years

Problem: Summers are generally warm and sometimes hot. London's average July high is 24 C (75.2 F). On average London will see 31 days above 25 C (77.0 F) each year, and 4.2 days above 30.0 C (86.0 F) every year. During the 2003 European heat wave there were 14 consecutive days above 30 C (86.0 F) and 2 consecutive days where temperatures reached 38 C (100.4 F), leading to hundreds of heat related deaths. Winters are generally cool and damp with little temperature variation. Snowfall does occur from time to time, and can cause travel disruption when this happens. Spring and autumn are mixed seasons and can be pleasant. As a large city, London has a considerable urban heat island effect, making the centre of London at times 5 C (9 F) warmer than the suburbs and outskirts. The effect of this can be seen below when comparing London Heathrow, 15 miles west of London, with the London Weather Centre, in the city centre.
How far from the center of London is London Heathrow Airport?
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Answer:
15 miles west