1. Physical Quantities, Units & Measurements Flashcards
Physical Quantity
Definition
A physical quantity is quantity that can be measured, consisting of a numerical magnitude and a unit.
7 Base Quantities
What they are + SI units + Symbols for units
Length - metre (m)
Mass - kilogram (kg)
Time - seconds (s)
Temperature - kelvin (K)
Electric current - ampere (A)
Amount of substance - mole (mol)
Luminosity - candela (cd)
Any other physical quantities are derived quantities that can be obtained through equations.
Prefixes for Multiples
Prefix + Symbol + Factor
kilo- (k): 1 thousand 103
mega- (M): 1 million 106
giga- (G): 1 billion 109
tera- (T): 1 trillion 1012
Prefixes for Sub-Multiples
Prefix + Symbol + Factor
deci- (d): 1 tenth 10-1
centi- (c): 1 hundredth -2
milli- (m): 1 thousandth 10-3
micro- (µ): 1 millionth 10-6
nano- (n): 1 billionth 10-9
State the magnitude of:
- Radius of a hydrogen nucleus
- Diameter of a typical atom
- Average width of human hair
- Diameter of wire
- Length of chopsticks
- Height of Mount Everest
- Diameter of Earth
- Radius of a hydrogen nucleus (0.000001nm OR 10-15m)
- Diameter of a typical atom (0.000,000,000,1m OR 0.1nm)
- Average width of human hair (0.000,1m OR 0.1mm)
- Diameter of wire (0.002m OR 2mm)
- Length of chopsticks (0.2m OR 20cm)
- Height of Mount Everest (8,848m OR ~ 9km)
- Diameter of Earth (12,700,000m OR 12.7 Mm)
Measuring Tape
Range + Smallest division + Record to nearest + Examples
Range: 0 to several metres
Smallest division: 0.1cm (1mm)
Record to nearest: 0.1cm (1mm)
Can be used to measure a person’s waist because it is flexible
Metre Rule
Range + Smallest division + Record to nearest + Examples
Range: 0 to 1 metre
Smallest division: 0.1cm (1mm)
Record to nearest: 0.1cm (1mm)
Can be used to measure the height of a table
Precautions when Using Metre Rule
Avoid using the zero mark of the metre rule as a start point to take measurements. This is because wear and tear may make it unsuitable for measuring purposes. The worn end may introduce errors to the readings.
Digital Calipers
Range + Smallest division + Record to nearest + Examples
Range: 0 to 15 centimetres
Smallest division: 0.001cm (0.01mm)
Record to nearest: 0.01cm (0.1mm)
Can be used to measure external diameter, internal diameter, or depth of a test tube
How to use Digital Calipers + Precautions
Inside jaws are used to measure internal diameter
Outside jaws are used to measure external diameter
Tail is used to measure depth
Precautions:
- Ensure that when the jaws are closed, the display should show a reading of zero (0.000cm or 0.00mm). If not, there is a zero error.
- The digital calipers must be reset to zero (using the zero button) before measurements are taken.
- If there is no zero button, subtract the zero error from the measured length to get the actual length.
Digital Micrometer Screw Gauge
Range + Smallest division + Record to nearest + Examples
Range: 0 to 2.5 centimetres
Smallest division: 0.0001cm (0.001mm)
Record to nearest: 0.001cm (0.01mm)
Can be used to measure the diameter of a wire
How to use Digital Micrometer Screw Gauge + Precautions
Turn the thimble until the anvil and spindle gently touch the object. Turn the ratchet until it clicks once. This prevents over-tightening of the digital micrometer screw gauge.
Precautions:
- Ensure that when the anvil and spindle touch each other, the display should show a reading of zero (0.0000cm or 0.000mm). If not, there is a zero error.
- The digital micrometer screw gauge must be reset to zero (using the zero button) before measures are taken.
- If there is no zero button, subtract the zero error from the measured length to get the actual length.
How to Reduce Parallax Error
Eye should be positioned such that the line of sight is perpendicular to the mark on the scale.
Period of a Pendulum
Definition
The time taken for one complete oscillation.
Why is it more accurate to measure the time taken for 20 complete oscillations and dividing the total time by 20 than just 1 oscillation?
It gives a smaller proportion of the same human reaction time in the result.
