Chapter 1: Physical quantities and measurements Flashcards
What is a physical quantity?
A property that can be measured
consists of a numerical magnitude and unit
What are the base/ fundamental quantities and their S.I unit symbols?
1) Mass, m - kilograms - kg
2) Length, L - metres - m
3) Time, t - seconds - s
4) Temperature, T - Kelvin - K
5) Electrical current, I - Ampere - A
6) Amt. of substance, n - mole - mol
7) Luminous intensity, lv - candela - cd
What are the derived quantities in S.I unit and in terms of fundamental S.I units?
1) Area, A - m^2 - m^2
2) Volume, V - m^3 - m^3
3) Density, p - kg m-3 - kg m-3
4) Velocity, v - m s-1 - m s-1
5) accel, a - m s-2 - m s-2
6) force, F - N - kg m-1 s-2
7) pressure, p - Pa - kg m-1 s-2
8) energy, E - J - kg m2 s-2
9) power, P - W - kg m2 s-3
10) frequency, f - Hz - s-1
11) moment, M - N m- kg m2 s-2
Define density
The mass per unit volume of a substance
p = mass/vol
pave = total mass/ total vol
S.I unit symbol = kg m-3
Contrast random errors and systematic errors
Random error
- Causes readings to be larger or smaller than true value by VARYING AMOUNTS
- CANNOT be eliminated, but can be REDUCED by taking repeated readings and calculating the average value
Systematic error
- Causes readings to always be larger or smaller than the true value by a FIXED AMOUNT
- CAN be eliminated by subtracting the source of the error or replacing the faulty equipment
Examples of random errors
Human reaction time - need to take repeated readings, record up to 2 d.p, find average
Parallax error - take repeated readings and calc. ave val
Examples of systematic errors
Zero error on vernier calliper - fix it by moving the thing or taking the initial error reading and adding or subtracting it to the final reading
Error due to wrong calibration of equipment
Contrast precision and accuracy
Precision:
- How close REPEATED readings are to ONE ANOTHER
- Precise readings have a small RANDOM error
* can only be assessed if there is more than one repeated reading
Accuracy:
- How close (THE AVE. OF) readings are to the TRUE VALUE
- Accurate readings have a small SYSTEMATIC error
Basic precision of measuring instruments
Metre-rule = 1mm/0.1cm
Vernier callipers = 0.1mm/ 0.01cm
Micrometre = 0.01mm/0.001cm
Electronic balance = 0.1g (measures up to 2 d.p but only the f1st d.p doesn’t fluctuate)
Measuring cylinder = 0.5ml
Stopwatch = 0.1s (human reaction time: no human can achieve the level of precision of the stopwatch so our human failings negates the tool’s ability –> 2 d.p)
Thermometer = 0.5 ˚C
Graph = 1/2 the smallest square
