Chapter 1 – Physical Quantities and Measurements

Question-and-answer flashcards covering key points from Chapter 1 on physical quantities, SI units, measurement instruments, errors, uncertainty, significant figures, and related concepts.

What distinguishes a physical quantity from a non-physical quantity?

A physical quantity can be measured with an instrument and expressed as a number with a unit; a non-physical quantity cannot be directly measured and is described qualitatively.

Give two examples each of physical and non-physical quantities.

Physical: length, temperature. Non-physical: love, beauty.

What two parts must every measurement contain?

A numerical magnitude and a unit.

Define base physical quantity.

A fundamental quantity chosen by convention that cannot be expressed in terms of other physical quantities.

Define derived physical quantity.

A quantity that can be expressed as a combination of one or more base quantities.

List the seven SI base quantities with their units.

Length (metre, m); Mass (kilogram, kg); Time (second, s); Electric current (ampere, A); Thermodynamic temperature (kelvin, K); Amount of substance (mole, mol); Luminous intensity (candela, cd).

Why is kilogram unusual among base units?

It is the only SI base unit that already contains a prefix (kilo).

What is the SI derived unit of force?

The newton (N) = kg·m·s⁻²

Express the pascal (Pa) in base SI units.

Pa = N·m⁻² = kg·m⁻¹·s⁻²

Express the coulomb (C) in base SI units.

C = A·s

State the purpose of SI prefixes.

They conveniently express very large or very small multiples of units by powers of ten.

What power of ten does the prefix giga represent?

10^9

Convert 50000000 m using an SI prefix.

5 × 10⁷ m = 50 Mm (megametres).

Write 0.00004 m in scientific notation.

4 × 10⁻⁵ m

What is scientific notation?

A way of writing numbers as a coefficient between 1 and 9 multiplied by a power of ten to simplify very large or small values.

State the rule for adding or subtracting numbers in scientific notation.

The exponents must be the same before the coefficients are added or subtracted.

Define least count of an instrument.

The smallest value that can be measured accurately with the instrument.

What is the least count of a standard laboratory metre rule?

1 mm (0.1 cm).

Explain parallax error.

Error that occurs when an instrument scale is read from an angle rather than with the eye perpendicular to the scale.

How can parallax error be avoided?

Place the eye directly above the marking being read, perpendicular to the scale.

State the two scales on Vernier callipers.

Main scale (1 mm divisions) and Vernier (sliding) scale (10 divisions over 9 mm).

Calculate the least count of typical Vernier callipers.

Least count = 1 MSD – 1 VSD = 1 mm – 0.9 mm = 0.1 mm.

What formula is used to find length with Vernier callipers?

Length = Main scale reading + (Vernier scale division × Least count).

Describe positive zero error in Vernier callipers.

When the Vernier zero lies to the right of the main-scale zero with jaws closed; it is subtracted from readings.

Describe negative zero error in Vernier callipers.

When the Vernier zero lies to the left of the main-scale zero with jaws closed; it is added to readings.

State two uses of Vernier callipers.

Measuring external diameter/thickness and internal diameter/depth of objects.

What are the two scales on a micrometer screw gauge?

Main (sleeve) scale with 0.5 mm divisions and circular (thimble) scale with 50 divisions.

Define pitch of a screw gauge.

The distance the spindle moves forward in one complete turn of the thimble (commonly 0.5 mm).

Calculate the least count of a screw gauge with 0.5 mm pitch and 50 divisions.

Least count = Pitch ÷ Number of divisions = 0.5 mm ÷ 50 = 0.01 mm.

Give the formula for thickness using a screw gauge.

Thickness = Main scale reading + (Circular scale reading × Least count) ± zero error.

Differentiate mass and weight.

Mass measures quantity of matter (kg); weight is the gravitational force on that mass (newtons).

Which instrument is commonly used in labs to measure mass precisely?

A physical (beam) balance or digital electronic balance.

What is the least count of a typical mechanical stopwatch?

0.1 s (one-tenth of a second).

State the rule for reading liquid levels in a measuring cylinder.

Keep the cylinder on a level surface and read at eye level with the bottom of the meniscus for concave liquids (e.g., water).

Explain how to measure volume of an irregular solid by displacement.

Record initial liquid level, submerge the solid, record new level; the difference equals the solid’s volume.

Why might a displacement can be preferred over a measuring cylinder?

It accommodates solids too large to fit into a cylinder and collects overflow water for volume measurement.

List the three main categories of experimental error.

Human (personal) errors, systematic errors, and random errors.

Give one example of each error type: personal, systematic, random.

Personal: mis-reading a scale. Systematic: zero error on an instrument. Random: fluctuations in temperature affecting measurements.

How can random errors be minimised?

Take many readings and use the average (mean) value.

Define uncertainty of a measurement.

The range within which the true value is expected to lie, due to limitations of the measuring instrument and method.

What are significant figures?

All reliably known digits in a measurement plus the first doubtful (estimated) digit.

State the rule for zeros between non-zero digits regarding significant figures.

Zeros between non-zero digits are always significant.

How many significant figures are in 0.00450 m?

3

Distinguish precision from accuracy.

Precision refers to how close repeated measurements are to each other; accuracy refers to how close a measurement is to the true value.

How does least count affect precision?

A smaller least count increases the precision of the instrument.

Explain the basic rule for rounding off when the digit following the last retained digit is greater than 5.

Increase the last retained digit by one.

When rounding 4.45 × 10² m to two significant figures, what result is obtained and why?

4.4 × 10² m because the digit before the dropped 5 is even, so it remains unchanged.

Provide two writing conventions for SI unit symbols.

Symbols are case-sensitive and never pluralised (e.g., 5 kg, not 5 kgs); a prefix is written directly before the unit symbol (e.g., mm, not m m).