Lesson 1 Introduction to IB Physics Scientific notation Orders of magnitude Estimation

IB Physics

Some information at the start of the course

New syllabus

Examinations SL HL Paper 1 20% Paper 2 40% 36% Paper 3 24% Internal assessment

Examinations Paper 1 (Multiple Choice) Paper 2 (Extended response) Paper 3 (Option (30 marks) and “data response” question (15 marks))

Examinations Paper 1 (Multiple Choice) 45mins SL 1 hr HL Paper 2 (Extended response) 1¼ hr SL, 2¼ hr HL Paper 3 (Options + data) 1 hr SL 1¼ HL Coursework SL-40 hours HL-60 hours

Internal Assessment

All lessons are on Moodle

Folders

Data Booklet

Text books

Topic 1 – Measurement and uncertainties Use the syllabus particularly when studying for examinations The DEFINITIONS you will have to learn ‘by heart’. At this stage I normally give out copies of the syllabus and definitions that need to be learnt.

Ranges of sizes, masses and times

Large/small numbers The number of atoms in 12g of carbon is approximately 600000000000000000000000 This can be written as 6.0 x 1023

Order of magnitude We can say to the nearest order of magnitude (nearest power of 10) that the number of atoms in 12g of carbon is 1024 (6.0 x 1023 is 1 x 1024 to one significant figure)

Small numbers Similarly the length of a virus is 2.3 x 10-8 m. We can say to the nearest order of magnitude the length of a virus is 10-8 m.

Ranges of sizes, masses and times You need to have an idea of the ranges of sizes, masses and times that occur in the universe.

Size/length Can you think of 10 objects? Can you then list them in order of decreasing length? http://www.joemonster.org/gry/41805/Scale_of_the_Universe_2

Size/length What size is the smallest object on your list to the nearest order of magnitude?

Size/length The smallest objects that you need to consider in IB physics are subatomic particles (protons and neutrons). These have a size (to the nearest order of magnitude) of 10-15 m. ( 1 x 10-15m) BE CAREFUL when putting into a calculator

Size/length What is the size/length of the largest object on your list to the nearest order of magnitude?

Size/length The largest object that you need to consider in IB physics is the Universe. The observable Universe has a size (to the nearest order of magnitude) of 1025 m.

Let’s try and get our head around that! Scale of the Universe - Joe Monster http://www.joemonster.org/gry/41805/Scale_of_the_Universe_2

On your paper can you estimate the masses of the largest and smallest objects you have written?

Mass The lightest particle you have to consider is the electron. What do you think the mass of the electron is? 10-30 kg! (0.000000000000000000000000000001 kg)

Mass We have already decided that the Universe is the largest object. What do you think its mass is? 1050 kg (100000000000000000000000000000000000000000000000000 kg)

Time Now think of 5 time intervals and put them in order (longest first) (For example, human lifetime, dog lifetime, time to walk home etc.)

Time The smallest time interval you need to know is the time it takes light to travel across a nucleus. Can you estimate it? 10-24 seconds

Time What’s the longest time interval you thought of?

Time The age of the universe. Any ideas?

Time The age of the universe. 12 -14 billion years 1018 seconds

Copy please! Size 10-15 m to 1025 m (subatomic particles to the extent of the visible universe) Mass 10-30 kg to 1050 kg (mass of electron to the mass of the Universe) Time 10-23 s to 1018 s (time for light to cross a nucleus to the age of the Universe)

A common ratio – Learn this! Hydrogen atom ≈ 10-10 m Proton ≈ 10-15 m Ratio of diameter of a hydrogen atom to its nucleus = 10-10/10-15 = 105

Estimation For IB you have to be able to make order of magnitude estimates.

Estimation/Guess What’s the difference between an estimation and a guess? Claudia Schiffer – the “Guess jeans girl” – see “Wayne’s World”!

Estimate the following: (to the nearest order of magnitude) The mass of an apple

Estimate the following: (to the nearest order of magnitude) The mass of an apple The number of times a human heart beats in a lifetime.

Estimate the following: (to the nearest order of magnitude) The mass of an apple The number of times a human heart beats in a lifetime. The speed a cockroach can run. A fast South American one!

Estimate the following: (to the nearest order of magnitude) The mass of an apple The number of times a human heart beats in a lifetime. The speed a cockroach can run. The number of times the earth will fit into the sun (Rs = 6.96 x 108 m, Re = 6.35 x 106 m)

Estimate the following: (to the nearest order of magnitude) The mass of an apple 10-1 kg The number of times a human heart beats in a lifetime. The speed a cockroach can run. The number of times the earth will fit into the sun (Rs = 6.96 x 108, Re = 6.35 x 106)

Estimate the following: (to the nearest order of magnitude) The mass of an apple 10-1 kg The number of times a human heart beats in a lifetime. 70x60x24x365x70=109 The speed a cockroach can run. The number of times the earth will fit into the sun (Rs = 6.96 x 108, Re = 6.35 x 106)

Estimate the following: (to the nearest order of magnitude) The mass of an apple 10-1 kg The number of times a human heart beats in a lifetime. 70x60x24x365x70=109 The speed a cockroach can run. 100 m/s The number of times the earth will fit into the sun (Rs = 6.96 x 108, Re = 6.35 x 106)

Estimate the following: (to the nearest order of magnitude) The mass of an apple 10-1 kg The number of times a human heart beats in a lifetime. 70x60x24x365x70=109 The speed a cockroach can run. 100 m/s The number of times the earth will fit into the sun (6.96 x 108)3/(6.35 x 106)3 = 106

Let’s do some more estimating! Complete the sheet “1.1 Estimating worksheet”. Students first estimate various quantities and then actually measure them to see how close their estimates are.

Let’s do some more estimating! Earth’s mass = 6 x 1024 kg Complete the sheet “1.1 Estimating worksheet”. Students first estimate various quantities and then actually measure them to see how close their estimates are.

Lesson 2 Fundamental and derived SI units Metric multipliers Significent figures

Do now! Can you continue the ‘Estimating’ sheet you started yesterday?

How many different units of length can you think of?

Units of length? Light year, light second, parsec, AU, mile, furlong, fathom, yard, feet, inches, Angstroms, nautical miles, cubits, cm, mm, km, μm, nm, ?

How long is a piece of string? Interesting BBC Horizon documentary on measurement (55 minutes) https://www.youtube.com/watch?v=r7x-RGfd0Yk How long is a piece of string?

The SI system of units There are seven fundamental base units which are clearly defined and on which all other derived units are based: You need to know these, but not their definitions.

The metre This is the unit of distance. It is the distance traveled by light in a vacuum in a time of 1/299792458 seconds.

The second This is the unit of time. A second is the duration of 9192631770 full oscillations of the electromagnetic radiation emitted in a transition between two hyperfine energy levels in the ground state of a caesium-133 atom. https://www.youtube.com/watch?annotation_id=annotation_2965246921&feature=iv&index=90&list=PLMrtJn-MOYmfqNgyPxx6NYMZnd25y4shc&src_vid=r7x-RGfd0Yk&v=NXRVtfCpLr4

Note that the Coulomb is NOT a base unit. The ampere This is the unit of electrical current. It is defined as that current which, when flowing in two parallel conductors 1 m apart, produces a force of 2 x 10-7 N on a length of 1 m of the conductors. Note that the Coulomb is NOT a base unit.

The kelvin This is the unit of temperature. It is 1/273.16 of the thermodynamic temperature of the triple point of water.

The mole One mole of a substance contains as many molecules as there are atoms in 12 g of carbon-12. This special number of molecules is called Avogadro’s number and equals 6.02 x 1023.

The candela (not used in IB) This is the unit of luminous intensity. It is the intensity of a source of frequency 5.40 x 1014 Hz emitting 1/683 W per steradian.

The kilogram This is the unit of mass. It is the mass of a certain quantity of a platinum-iridium alloy kept at the Bureau International des Poids et Mesures in France. THE kilogram!

Can you copy this please? SI Base Units Can you copy this please? Quantity Unit distance metre time second current ampere temperature kelvin quantity of substance mole luminous intensity candela mass kilogram Note: No Newton or Coulomb

Derived units Other physical quantities have units that are combinations of the fundamental units. Speed = distance/time = m.s-1 Acceleration = m.s-2 Force = mass x acceleration = kg.m.s-2 (called a Newton) (note in IB we write m.s-1 rather than m/s)

Checking equations If an equation is correct, the units on one side should equal the units on another. We can use base units to help us check.

Checking equations For example, the period of a pendulum is given by T = 2π l where l is the length in metres g and g is the acceleration due to gravity. In units m = s2 = s m.s-2

Some important derived units (learn these!) 1 N = kg.m.s-2 (F = ma) 1 J = kg.m2.s-2 (W = Force x distance) 1 W = kg.m2.s-3 (Power = energy/time) Guess what

Metric multipliers It is sometimes useful to express units that are related to the basic ones by powers of ten

Metric multipliers 10-18 atto a 101 deka da 10-15 femto f 102 hecto h Power Prefix Symbol Power Prefix Symbol 10-18 atto a 101 deka da 10-15 femto f 102 hecto h 10-12 pico p 103 kilo k 10-9 nano n 106 mega M 10-6 micro μ 109 giga G 10-3 milli m 1012 tera T 10-2 centi c 1015 peta P 10-1 deci d 1018 exa E

Metric multipliers 10-18 atto a 101 deka da 10-15 femto f 102 hecto h Don’t worry! These will all be in the formula book you have for the exam. Metric multipliers Power Prefix Symbol Power Prefix Symbol 10-18 atto a 101 deka da 10-15 femto f 102 hecto h 10-12 pico p 103 kilo k 10-9 nano n 106 mega M 10-6 micro μ 109 giga G 10-3 milli m 1012 tera T 10-2 centi c 1015 peta P 10-1 deci d 1018 exa E

Examples 3.3 mA = 3.3 x 10-3 A 545 nm = 545 x 10-9 m = 5.45 x 10-7 m 2.34 MW = 2.34 x 106 W Simply replace the prefix with the relevant power of 10.

Significant figures Start counting from the first non-zero number until the end of written numbers (including zeroes!) 0.0030 = 2 sf 0.00300 = 3 sf 0.003 = 1 sf

Significant figures Don’t count trailing zeroes with a number that does not contain a decimal point 1200 = 2 sf BUT 1200.0 = 5 sf

Significant figures The significance (see what I did there?!) of significant figures will be discussed in the next section on uncertainties.

Some questions Change 2360000 J to standard form in MJ. A radio station has a frequency of 1090000 Hz. Change this to standard form in MHz. The average wavelength of light is 5.0 x 10-7 m. What is this in nanometres? What is 1 x 10-8 seconds in microseconds?