Matter & Forces. Universe by Numbers: Day 2 July 2016 Dr Andrew French

Transcription

1 Matter & Forces Universe by Numbers: Day 2 July 2016 Dr Andrew French

2

3 Length scales Glucose molecule m m 9 10 m 8 10 m Antibody 7 10 m Virus 6 10 m Bacterium

4 5 10 m Human cell 2 10 m Human eye 1m Plant cell

5 4 10 m 2 10 m 9 10 m 6 10 m 7 10 m Earth diameter = 12,756km

6 4 10 m

7 9 10 m R 610 m 1AU m

8 m 1 light year m

9 26 10 m 1 light year m About 2 million Milky Ways correspond to the diameter of this sphere!

10 The size of an atom Earth diameter = 12,756km 3 Marble diameter = 3.6cm Volume of Earth in marbles There are as many atoms in a marble as an Earth made of marbles! Atomic diameter is about 1 Ångström Number of atoms in a marble 25

11 Mostly empty space! Atomic mass and density m m m e p n kg kg kg Anders Ångström This is one Ångström water kg ,200 kgm 10 1,000 kgm -3 3

12 Higgs boson discovered at CERN in July 2012 All particles are within the Higgs field. Interactions with it confer mass to certain particles. Peter Higgs 1929-

13 At CERN, particles (such as protons) are collided at very high energies. The high energies are achieved via acceleration using electric fields. Enormous* voltages are used! Magnetic fields are used to steer the particle beams in the circular beamlines * volts When particles such as protons collide, a plethora of other particles (i.e. hadrons or leptons) are formed. The trajectories of these particles can be used to infer the mass and charge of these particles

14 The Standard Model of Particle Physics Fermions are particles with halfinteger spin They obey the Pauli Exclusion Principle Leptons Spin half Matter Hadrons (made from quarks) Baryons (three quarks) Half-integer spin proton = uud neutron = udd Mesons (quark + anti-quark pair) Integer spin Mesons are also Bosons as they have integer spin. They don t have to obey the Pauli Exclusion Principle Interactions between particles proceed via exchange of Gauge Bosons e.g. photon, W +, W -, Z o, gluon, graviton(?)

15

16 Standard model interaction map

17 Forces A weighty puss indeed... F F The strong and weak forces bind the particles together within the atomic nucleus Electrical forces bind atoms together to form molecules. mg Gravity acts on all mass Magnetism is the electrical force resulting from moving charge Groups of atoms result in the macroscopic forces we experience (i.e. friction)

18 Explaining Chemistry Dmitri Mendeleev Wolfgang Pauli

19

20 Each different type of atom is called a nuclide Atomic number (Z) = number of protons. This defines an element Carbon 12 has: 6 protons 6 electrons 6 neutrons Binding energy The number of neutrons defines an isotope of an element The atomic mass (A) is approximately the number of protons + the number of neutrons but not exactly... Iron 56 has: 26 protons 26 electrons 30 neutrons

21 Alpha decay Beta decay He 2+

22 Time taken for half a sample to decay half lives The decay of atomic nuclei is a random process The decay rate is proportional to the number of radioactive elements in a sample

23 Antoine Henri Becquerel Spontaneous radioactivity in Uranium salts Marie Curie Theory of radioactivity Isolation of isotopes

24 Allow electrons to pass through them Conductor when hot insulator when cold Good thermal conductors Electrons tightly held by atoms, but can be transferred by rubbing

25 Plastic wire insulator Metals are good conductors as electrons can move easily within them Insulators (such as plastics) are often polymers formed from a network of covalent bonds. It is much harder to extract electrons from them! Copper wire. metallic bonding of atoms so a good electrical (and heat) conductor

26

27

28 Walking a can with a charged polythene rod Rubbing a polythene rod transfers Induced charges by the presence of the rod Normal neutral situation of an uncharged can Placing the negatively charged rod near a metal can will cause the lightly held electrons on it to be repelled, leaving a net positive charge. The positively charged can will therefore roll towards the negatively charged rod. electrons to it. Polythene is an insulator so the charge remains on the surface (rather than flowing to ground if it were a conductor).

29 Charge on the electron is -e e C 1 amp means 1 coloumb of charges flows per second Q It Q charge I current t time Charles-Augustin de Coulomb

30

31 1 amp means 1 coloumb of charges flows per second Q It

32 Make a lemon battery

33 *German School Teacher Georg Ohm* R V IR Ohm s Law V I

34 I V R1 R2 V1 V2 I The same current must flow through every component in the loop, otherwise charge would be created or lost! V V V IR 1 1 IR IR 2 2 Apply Ohm s law to entire series loop. R is the total resistance Apply Ohm s law to each resistor in turn V V V 1 2 The applied voltage V must be divided across the resistors, since this relates to the total energy supplied per unit charge moved Hence: IR IR IR 1 2 R R R 1 2 so series resistors add

35 I 2 I I 1 I 2 V R 1 V R 2 I V V V IR I R 1 1 I R 2 2 Apply Ohm s law to entire circuit. R is the total resistance Apply Ohm s law to each resistor in turn. Same electric field across each loop, so same voltage dropped across the resistors V Current is assumed to be contained within the circuit, hence: I I I 1 2 Therefore: V / R V / R V / R R R R This is Kirchoff s law so parallel resistor loop resistance reciprocals add

36 R g moon moon R m 1.63ms 3359 kgm -2-3 Newton s law of universal gravitation states that the gravitational field strength at a distance R from a spherical object is proportional to the mass contained within a sphere of radius R centred on the object and inversely proportional to R 2 g GM 2 R G = 6.67 x m 3 kg -1 s -2 M 4 3 If a planet has uniform density G 4 3 g 2 3 R R g GR 4 3 R g earth earth 3 R m 9.81ms kgm R g moon moon m 1.63ms kgm -3 Isaac Newton

37 Force of gravity Isaac Newton ( ) developed a mathematical model of Gravity which predicted the elliptical orbits proposed by Kepler Planet and Solar masses GMM F 2 r G m kg s a Semi-major axis r P b 1 a a 1 1 cos Polar equation of ellipse Eccentricity of ellipse 4 a G( M M ) Orbital period P Semiminor axis M r F 2 r 2b M GMM

38

39 Topics to reflect on: Length scales. Size of an atomic nucleus, atom, molecule, virus, bacteria, cell, human, county, country, Earth, Star, Solar System, Galaxy, Universe! Atoms, electrons, neutrons, protons, quarks... Forces: Nuclear (strong, weak), Electrical, Gravity Periodic table. Atomic numbers. Radioactivity Electrical forces, charge and electricity Effects of gravity and orbits Depending on your course, we may not cover all of these. Review the topics you did meet. If you have time to spare, read on!