Enrico FermiA Modern

Renaissance Man

FOT 2010

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Enrico Fermi, Physicist

Fermi was one of the greatest physicists of the 20th century.

He is best known for his leading contributions in the Manhattan Project but his work spanned every field of physics.

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Early YearsIn 1901, Enrico was born in Rome to Alberto Fermi, a

Chief Inspector of the Ministry of Communications, and Ida de Gattis, an elementary school teacher.

As a young boy he enjoyed learning physics and mathematics and shared his interests with his older brother, Giulio. When Giulio died unexpectedly of a throat abscess in 1915 it brought great sorrow to the family and Enrico escaped into his studies.

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Fermi Electron TheoryFermi and his friends had a

reputation as pranksters.One afternoon, while trapping

geckos (used to scare girls at the university), Fermi developed the fundamental theory for electrons in solids.

Fermi’s theory later became the foundation of the entire semiconductor industry.

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Fermi ProblemsFermi was famous for being able to avoid long,

tedious calculations or difficult experimental measurements by devising ingenious ways of finding approximate answers.

He also enjoyed challenging his friends with “Fermi Problems” that could be solved by such “back of the envelope” estimates.

Laura and Enrico FermiBaltimore Polytechnic Institute Engineering

Fermi Problem Example

“What is the length of the equator?”

Fermi problems are solved by assembling simple facts that combine to give the answer:

•The distance from Los Angeles to New York is about 3000 miles.• These cities are three time zones apart.• So each time zone is about 1000 miles wide.• There are 24 time zones around the world.• So the length of the equator must be about 24,000 miles

The exact answer is 24,901 miles.

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Ping Pong Anyone?

Solving a problem in 60 seconds (individually)Look around the room you are sitting in. Take just 60 seconds to

answer the following questions:How many ping-pong balls could you fit into the room?

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Ping Pong Anyone?

Solving a problem in 60 seconds (individually)Look around the room you are sitting in. Take just 60 seconds to

answer the following questions:How many ping-pong balls could you fit into the room?

What was your model of a ping-pong ball? What was your model of the room?

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Ping Pong Anyone?

Solving a problem in 60 seconds (individually)Look around the room you are sitting in. Take just 60 seconds to

answer the following questions:How many ping-pong balls could you fit into the room?

What was your model of a ping-pong ball? What was your model of the room?

What other simplifications or assumptions did you make?

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Fermi Problems

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• Open ended problem solving.• Thought process is more important than

calculating exact answer.• Steps in solving Fermi problems– Determine what factors are important in solving

problem– Estimate these factors– Use dimensional reasoning to calculate a solution

Fermi Problems

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• What do Fermi Problems have to do with engineering– Engineers have to solve open ended problems

that might not have a single right solution– Engineers have to estimate a solution to a

complicated problem– Engineers have to think creatively

The Fermi ParadoxThe extreme age of the universe and its vast

number of stars suggest that if the Earth is typical, extraterrestrial life should be common.

Discussing this proposition with colleagues over lunch in 1950, Fermi asked: "Where is everybody?”

We still don’t have agood answer to Enrico’squestion.

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Homework- Due tomorrow

• The physicist Enrico Fermi enjoyed posing questions like these to his students and colleagues.

• Pick one part (either a or b) from each of the following two questions, and make the best possible estimate for the situation. Your answer will be a combination of several quantities. Be sure to specify what assumptions you have made in arriving at your estimate.

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Homework continued

• 1. a. How long do you think it would take you to eat your

weight in food?

or

b. What is the weight of all the trash produced in your house in a year?

Write all your assumptions and calculations

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Homework continued

• 2. a. How many hot dogs do you think are sold in a baseball season at Oriole Park?

or• b. How many times does a person's heart beat

in a lifetime?

Write all your assumptions and calculations

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