[ RadSafe ] FW: What the Prez Should Know

[Mercado, Don]

Quite interesting but appropriate.

 

Climate politics: What every president should know p345
If you want to lead the free world, you'd better know your physics. That's the lesson from a popular undergraduate class, called 'Physics for future presidents', taught by Richard A. Muller at the University of California, Berkeley. Here he sets some typical questions. An interactive version of this quiz with extended answers is online at http://ealerts.nature.com/cgi-bin24/DM/y/hhax0SpR8f0HjB0BgsS0EI

 

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CLIMATE POLITICS SUPPLEMENTARY TEXT

What every president should know

Here are the answers to the questions set by Richard A. Muller in our physics for presidents quiz.

1) Electricity from the wall plug costs about 10 cents per kilowatt-hour (kWh). If you were to get the same electricity by buying AAA alkaline batteries at the local store, the cost of that electricity would be:

(a) 15 cents per kWh

(b) 94 cents per kWh

(c) $2.50 per kWh

(d) $1,000 per kWh

The correct answer is (d)

A $1.50 AAA battery delivers about 1 ampere for 1 hour at 1.5 volts — an energy of 1.5 watt-hour. That means it costs $1 per watt-hour, or $1,000 per kilowatt-hour. People sometimes complain about the high cost of electricity, but in fact it is 10,000 times cheaper than battery power.

2) A gram of which of these is most toxic?

(a) Botulinum toxin

(b) Arsenic

(c) Anthrax spores

(d) Plutonium dust (inhaled)

The correct answer is (a)

The LD50 dose (lethal 50% of the time) for botulinum toxin is about 70 nanograms for a 75 kg person. Plutonium (by urban legend the most toxic substance known to man) is very toxic — comparable to arsenic if ingested, worse than anthrax if breathed — but not as bad as botulinum toxin by a factor of more than 1,000.

3) The highest achieved efficiency (solar energy converted to electrical energy) of solar cells is approximately:

(a) 4%

(b) 15%

(c) 28%

(d) 41%

The correct answer is (d)

Inexpensive solar cells give an efficiency of 10–15%, but the best ones deliver 41% efficiency. The catch is that these cells cost $10 per square centimetre.

4) A typical high-resolution spy satellite has how long to photograph a location?

(a) 10 seconds

(b) 1 minute

(c) 12 minutes

(d) 90 minutes

The correct answer is (b)

High-resolution spy satellites fly low (250 km) to get close to their targets. Their velocity is 25,000 kilometres per hour, so they are above their target (from −250 km to +250 km) for only 72 seconds.

5) The dose for radiation illness (50% chance of death within a month) is 300 rem, whole body. The dose to trigger on average one cancer is:

(a) 2.5 rem

(b) 25 rem

(c) 250 rem

(d) 2,500 rem

The correct answer is (d)

For doses between 25 rem and 200 rem, the cancer rate in survivors increases by an amount approximately proportional to the dose. Add up the doses given to a group of people, and for every 2,500 whole-person-rem, there is an excess of about one cancer. 

6) Compared with a gallon of gasoline, the energy supplied by a gallon of liquid hydrogen is approximately:

(a) ⅓ (that is, it has less energy per gallon)

(b) The same energy per gallon

(c) 3 times more energy per gallon

(d) 12 times more energy per gallon

The correct answer is (a)

Hydrogen delivers 26 kilocalories per gram (not counting the oxygen required for a burn) versus 10 kilocalories per gram for gasoline (again, not counting the oxygen). But gasoline is more than 10 times as dense as liquid hydrogen.

7) Compared with the energy released when a pound of gasoline is burnt, the energy released when a pound of TNT is exploded is about:

(a) 2 times greater

(b) 13 times greater

(c) the same, within 40%

(d) less by a factor of 15

The correct answer is (d)

There is a solid physics reason why we are so hooked on gasoline. It has huge energy per gram (10 kilocalories), much more than TNT (0.6 kilocalories). TNT is not used because of the high energy density it delivers, but because it can deliver it quickly, increasing the force of a blast.

8) Of the deaths caused by the Hiroshima atomic bomb, the fraction attributed to cancer was:

(a) Less than 2%

(b) About 7%

(c) About 20%

(d) More than 50%

The correct answer is (a). 

Some 120,000 survivors were exposed to significant levels of radiation in the Hiroshima and Nagasaki explosions. The best estimate is that these survivors received an average dose of 20 rem, resulting in 960 cases of cancer. That’s horrific, but less than 1% of the 100,000 who died in the blast.

9) A critical mass of plutonium has a volume of:

(a) 3 tablespoons

(b) 1 soft-drink can

(c) 1 gallon

(d) 3 gallons

The correct answer is (b)

The Los Alamos Primer (Univ. California Press) says that the mass of plutonium in the Nagasaki bomb was 6 kilograms, which would fit into 300 cm3. Even if it was the low-density phase of plutonium, it would still fit in a 12-oz soda can, which has a volume of 355 cm3.

10) In one computer cycle (a billionth of a second for a slow laptop), light travels about:

(a) 1 foot (30 centimetres)

(b) 300 metres

(c) 3 kilometres

(d) 300 kilometres

The correct answer is (a)

3×108 m sec−1 = 30 centimetres or 1 foot per nanosecond. A Mac Powerbook has a clock rate of 2 GHz: in one cycle, light can travel at most 15 cm, and electric signals typically travel less. That’s why computers must be small.

11) In the past 100 years, the carbon dioxide level in Earth’s atmosphere has 

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increased by what fraction of its previous value?

(a) Less than 1%

(b) 3%

(c) 30%

(d) 112%

The correct answer is (c)

The current level of carbon dioxide in the atmosphere is about 380 p.p.m.. A hundred years ago, the level was 300 p.p.m. (measured in old ice), so we have gone up 26%. If we compare instead with the long-term historical level (before the industrial revolution) when the level was 280 p.p.m., then we are up 36%. 

12) The rocket that won the X Prize in 2004 achieved an altitude of 100 kilometres. To go into orbit would require more energy. How much more?

(a) 1.414 times more

(b) 2 times more

(c) 7 times more

(d) 32 times more

The correct answer is (d)

The energy to get a mass m to h = 100 km is E100 = mgh, where g is the acceleration of gravity (9.8 m sec−2). The energy EO to orbit is ½ the escape energy, so EO = ½mGM/R = ½mgR, where G is the gravitational constant, M is Earth’s mass and R is Earth’s radius. The ratio is EO/E100 = ½R/h = ½(6,378/100) = 32.

13) The International Atomic Energy Agency’s 2006 estimate for the number of excess cancer deaths expected worldwide from the Chernobyl nuclear accident was:

(a) Less than 1,000

(b) 4,000

(c) 24,000

(d) 1.3 million

The correct answer is (b)

The agency’s original estimate was that the world population had received a dose of 60 million whole-person-rem, leading to 24,000 deaths. But in 2006, it improved its dose estimate and concluded that the cancer deaths would total 4,000.

14) The ozone layer in the atmosphere is created by:

(a) Carbon dioxide

(b) Sunlight

(c) Sulphur from fossil fuels

(d) Chlorofluorocarbon compounds (such as Freon)

The correct answer is (b)

Ozone is created when the ultraviolet component of sunlight fissions oxygen molecules into atomic oxygen; these attach themselves to molecular oxygen creating ozone. CFCs act as a catalyst to destroy ozone.

15) Light in a fibre carries more information per second than electricity in a wire because:

(a) It has a higher frequency

(b) It travels faster than electricity

(c) It makes use of quantum effects

(d) It doesn’t. Wires transmit higher bit rates. (That’s why they are used in computers.)

The correct answer is (a)

By Shannon’s theorem, the number of bits per second is limited by the frequency. (In detail, it is the bandwidth and the signal-to-noise ratio, but the maximum frequency is the dominant term.)

16) The power in a square kilometre of sunlight is:

(a) 1 kilowatt

(b) 1 megawatt

(c) 10 megawatts

(d) 1 gigawatt

The correct answer is (d)

Sunlight delivers only 1 kilowatt per square metre: a little more than 1 horsepower, so not enough for any modern car. But a square kilometre has a million of those, putting it in the same category as nuclear-power plants. 

17) To be legal for consumption in the United States, the radioactivity of one litre of ethanol (drinking alcohol) must be:

(a) Less than 12 decays per minute

(b) Below the threshold of standard Geiger counters

(c) Not measurable by accelerator mass spectrometry (the most sensitive detection method)

(d) More than 4,000 decays per minute

The correct answer is (d). 

Drinking alcohol must be made from plants, and they (unlike fossil fuel) contain one part in 1012 of carbon-14, a radioactive isotope that decays with a half life of 5,730 years. One litre of ethanol (C2H5OH) has 412 grams of carbon and 4,940 decays per minute.

For more details on Richard Muller’s ‘Physics for future presidents’ class visit http://www.muller.lbl.gov/PffP.html