Chapter 1 Measurement Flashcards
What is a physical quantity?
A physical quantity is a quantity that can be measured, has a numerical magnitude and a unit (E.g. kg, m, s) Physical quantities consist of base quantities and derived quantities.
What are the 5 base quantities and their respective
(i) S.I. units
(ii) symbols for units?
- Length (S.I. unit: metre; symbol for unit; m)
- Mass (S.I. unit: kilogram; symbol for unit; kg)
- Time (S.I. unit: second; symbol for unit; s)
- Electric current (S.I. unit: ampere; symbol for unit: A)
- Thermodynamic temperature (S.I. unit: kelvin; symbol for unit: K)
List 4 derived quantities and their respective
(i) relations with base quantity
(ii) symbol for units
- Area
- Relation with base quantity: l x w
- Symbol for unit: m² - Volume
- Relation with base quantity: l x w x h
- Symbol for unit: m³ - Speed
- Relation with base quantity: distance/time
- Symbol for unit: m/s - Density
- Relation with base quantity: mass/ volume
- Symbol for unit: kg/m³
List the 8 prefixes and their respective
(i) symbols
(ii) factors
- nano (symbol: n; factor: 10⁻⁹)
- micro (symbol: µ; factor: 10⁻⁶)
- milli (symbol: m; factor: 10⁻³)
- centi (symbol: c; factor 10⁻²)
- deci (symbol: d; factor: 10⁻¹)
- kilo (symbol: k; factor: 10³)
- mega (symbol: M; factor: 10⁶)
- giga (symbol: G; factor: 10⁹)
List the 4 instruments used to measure length and the respective
(i) range of distances they are used to measure
(ii) precision
- Metre rule
- Distance ≤ 1 m
- Precision: 0.1 cm - Measuring tape
- Measures several metres
- Precision of 0.1 cm - Vernier calipers
- 1 cm ≤ Distance ≤ 15 cm
- Precision: 0.01 cm - Micrometer screw gauge
- Distance ≤ 2.5 cm
- Precision: 0.001 cm = 0.01 mm
How do we minimise errors of measurement?
- The eye must be positioned directly above the mark on the scale to avoid parallax error.
- Take several readings and calculate the average value.
What are the respective parts of a vernier caliper used for measuring?
- Outside jaws: Measure external diameter of disc
- Inside jaws: Measure internal diameter of tubes and containers
- Tail: Measure depth of tubes or containers.
List the steps taken to measure an object using a vernier caliper. (context: assume that we’re measuring the external diameter of a disc)
*Check for positive/ negative zero error!
- Grip the object gently using the outside jaws of the calipers.
- Read the main scale directly opposite the zero mark on the vernier scale.
- Check where the vernier mark coincides with a marking on the main scale.
- The length of the object is found by adding/ subtracting the vernier scale reading to/ from the main scale reading accordingly.
How do you tell if a zero error is positive or negative? (vernier caliper)
- Positive zero error: Zero mark on vernier is slightly to the right of the zero mark on the main scale
- Negative zero error: Zero mark on vernier is slightly to the left of the zero mark on the main scale (MUST COUNT FROM 10)
List the steps taken to measure an object using a micrometer screw gauge.
*Check for positive/ negative zero error!
- Turn the thimble until the anvil and the spindle gently grip the object. Then turn the ratchet until it starts to click.
- Read the main scale reading at the edge of the thimble.
- The thimble has 50 divisions, each of which is 0.01 mm. Take the thimble reading opposite the datum line of the main scale.
- The length of the object is found by adding the thimble scale reading to the main scale reading accordingly.
How do you tell if a zero error is positive or negative? (micrometer screw gauge)
- Positive zero error: Zero mark on datum line to the left
- Negative zero error: Zero mark on datum line to the right
(Check for the number of divisions FROM the ‘0’ mark regardless of whether positive or negative)
List the three precautions that need to be taken when using a micrometer screw gauge.
- When anvil and spindle is closed, check for zero error. Subtract the error from reading to get the actual reading.
- Do not overtighten. Close the gap between object and spindle using the ratchet instead of the thimble! The ratchet will produce a clicking sound, indicating the grip is just right.
- Take measurements at different locations and find the average reading. (e.g. take 3 diameter readings along entire length of thin wire, then find the average.)
What is the instrument used for measuring time and what is its:
(i) precision
(ii) human reaction time?
Digital stopwatch
- Precision: 0.01s
- Human reaction time: ± 0.3s
Describe a simple pendulum.
- Called a simple pendulum because it observes simple harmonic motion
- Oscillations are periodic in nature (after 1 period, it returns to its original position)
Define a period.
Period: time taken for one complete oscillation
