All 11 short questions of 9th Class Physics Chapter 1, Physical Quantities and Measurements, with exam-ready answers in the book's words. Punjab Board new syllabus.
Exam-ready answers. Learn the meaning, then write them in your own words.
No. A non-physical quantity cannot be measured with an instrument, because it has no standard unit. Examples are love, beauty, honesty and trust.
We can only judge such things in other ways, like a survey with ratings out of 10. These give an opinion score, not a physical measurement.
Measurement is the process of comparing an unknown quantity with a known standard quantity (a unit).
Its two parts are (1) a number (magnitude) and (2) a unit. In 5 m, the number is 5 and the unit is metre.
A standard unit means the same everywhere. It makes trade fair, keeps work accurate, and lets people everywhere share and compare results.
| Base quantities | Derived quantities |
|---|---|
| Length | Area |
| Mass | Volume |
| Time | Speed |
The metre (m), since it is the SI unit of length. A desk is about 0.75 m high; in everyday use we may also write this as 75 cm.
| Unit | Symbol | Measures |
|---|---|---|
| metre | m | length |
| kilogram | kg | mass |
| second | s | time |
| ampere | A | electric current |
| kelvin | K | temperature |
| mole | mol | amount of substance |
| candela | cd | luminous intensity |
Prefixes make very large and very small numbers short and easy to read and write. For example, 5000 m can be written as 5 km.
| Sub-multiples | Multiples |
|---|---|
| milli (m) = 10⁻³ | kilo (k) = 10³ |
| micro (µ) = 10⁻⁶ | mega (M) = 10⁶ |
| nano (n) = 10⁻⁹ | giga (G) = 10⁹ |
| Written | Meaning | Value |
|---|---|---|
| (a) 5 pm | 5 picometres | 5 × 10⁻¹² m |
| (b) 15 ns | 15 nanoseconds | 15 × 10⁻⁹ s = 1.5 × 10⁻⁸ s |
| (c) 6 µm | 6 micrometres | 6 × 10⁻⁶ m |
| (d) 5 fs | 5 femtoseconds | 5 × 10⁻¹⁵ s |
Look at the last letter: m means metre and s means second. Some keys write (d) in metres, which is wrong.
(a) To measure small lengths precisely, to 0.1 mm, such as the diameter of a pipe, the inner size of a test tube, or a small depth.
(b) The main scale and the vernier scale.
(c) Least count = 1 main scale division − 1 vernier division = 1 mm − 0.9 mm = 0.1 mm.
(d) When the jaws are closed, the zeros of the two scales should line up. If they do not, the instrument has a zero error.
Least count = 1 mm ÷ 10 = 0.1 mm = 0.01 cm.
For a main scale reading of 2.6 cm with the 4th vernier line lining up: length = 2.6 + (4 × 0.01) = 2.64 cm.
Solved keys disagree on this figure. One reads the 4th vernier line (2.64 cm), another the 5th (2.65 cm). Find which vernier line lines up in your book's figure and use that number in the same formula.
B is correct, because the eye is straight above the mark (at a right angle to the scale). A and C read from the side, so they have parallax error.
