1. Physical Quantities, Units & Measurements

Question 1

Define the 7 Base Quantities

& their SI units

Answer 1

Length - metre (m)
Mass - kilogram (kg)
Time - seconds (s)
Temperature - kelvin (K)
Electric current - ampere (A)
Amount of substance - mole (mol)
Luminosity - candela (cd)

Question 2

Prefixes for Multiples

Answer 2

kilo- (k): 1 thousand 10^3
mega- (M): 1 million 10^6
giga- (G): 1 billion 10^9
tera- (T): 1 trillion 10^12

Question 3

Prefixes for Sub-Multiples

Answer 3

deci- (d): 1 tenth 10^-1
centi- (c): 1 hundredth 10^-2
milli- (m): 1 thousandth 10^-3
micro- (µ): 1 millionth 10^-6
nano- (n): 1 billionth 10^-9

Question 4

State the magnitude of:

• Radius of a hydrogen nucleus
• Diameter of a typical atom
• Average width of human hair
• Length of chopsticks
• Height of Mount Everest
• Diameter of Earth

Answer 4

• Radius of a hydrogen nucleus (0.00001nm)
• Diameter of a typical atom (0.000,000,000,1m OR 0.1nm)
• Average width of human hair (0.000,1m OR 0.1mm)
• 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)

Question 5

Measuring Tape

Range, Smallest division, Record to nearest

Answer 5

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

Question 6

Metre Rule

Range, Smallest division, Record to nearest

Answer 6

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

Question 7

Precautions when Using Metre Rule

Answer 7

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.

Question 8

Digital Calipers

Range, Smallest division, Record to nearest

Answer 8

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

Question 9

How to use Digital Calipers + Precautions

Answer 9

Inside jaws are used to measure internal diameter
Outisde 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 measures are taken.
- If there is no zero button, subtract the zero error from the measured length to get the actual length.

Question 10

Digital Micrometre Screw Gauge

Range, Smallest division, Record to nearest

Answer 10

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

Question 11

How to use Digital Micrometer Screw Gauge + Precautions

Answer 11

Turn the thimble unti 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.

Question 12

How to Reduce Parallax Error

Answer 12

Eye should be positioned such that the line of sight is perpendicular to the mark on the scale.

Question 13

Period of a Pendulum

Definition

Answer 13

The time taken for one complete oscilation