1. Measurements & Uncertainty

Question 1

All the 7 base SI units

Answer 1

metre
kilogram
second
ampere
kelvin
mole
candela

Question 2

Approx. lengths of the following:
Neutron/proton
Atom
Wavelength of visible light
Earth's diameter
Earth to sun
Radius of observable universe

Answer 2

Answers:
10^-15m
10^-10m
10^-7m
10^7m
10^11m
10^27m

Question 3

Approx. timings of the following:
Passage of light across an atom
Time between heartbeats
One day
One year
Human life span
Age of universe

Answer 3

Answers:
10^-20s
10^0s
10^5s
3*10^7s
2*10^9s
10^19s

Question 4

Approx. masses of the following:
Electron
Proton/nucleus
DNA molecule
Mosquito
Earth
Sun
Total mass of observable universe

Answer 4

Answers:
10^-30kg
10^-27kg
10^-17kg
10^-5kg
6*10^24kg
2*10^30kg
10^52kg

Question 5

Approx. energies of the following:
E needed to remove electron from the surface of metal
KE of tennis ball during game
E in a lightning strike
E released in an earthquake
E radiated by sun in 1s

Answer 5

Answers:
10^-18J
10^0J
10^10J
10^20J
10^26J

Question 6

What causes random errors?

Answer 6

Unpredicted deviations of a measured value from the actual value

Question 7

What causes systematic errors?

Answer 7

Fixed shifts in measurements away from the actual value

Question 8

How to reduce random error?

Answer 8

Average repeated measurements

Question 9

How to reduce systematic error?

Answer 9

Cannot be reduced by taking average

Question 10

Precision vs Accuracy

Answer 10

Precision: Small scatter, low uncertainty
Accuracy: Close to the true value

Question 11

Express random & systematic errors in terms of precision and accuracy

Answer 11

Random errors: More accurate, less precise

Systematic errors: Less accurate, more precise

Question 12

How to get uncertainty of raw measurements

And one exception

Answer 12

Follow smallest division in the instrument (NOT HALF THE DIVISION)
EXCEPTION: Digital stopwatch measures to 0.01s, but take uncertainty as 0.1s since avg. human reaction time = 0.2s

Question 13

Uncertainty: Addition & subtration of measurements

Answer 13

Add the abs unc.

Question 14

Uncertainty: Multiplication & division of measurements

Answer 14

Add the fractional/percentage unc.

Question 15

What s.f. is uncertainty to

Answer 15

1 s.f.

Question 16

What is an easy way to find resultant vector?

Answer 16

Align head of force to tail of the other force

Question 17

What side of a triangle should a resultant vector always be?

Answer 17

Hypotenuse. Make sure that the resultant vector is always the largest force.

Question 18

Common random errors

Answer 18

Variations in fluctuating external conditions (temperature, humidity)
Variation in conditions in the measuring instruments

Question 19

Common systematic errors [3]

Answer 19

Human reaction time
Zero error of instruments
Extra counts in a GM counter due to background radiation