Class 9 Physics | Punjab Curriculum and Textbook Board Syllabus 2025
Physical quantities are quantities that can be measured directly or indirectly using tools and instruments, such as the length of an object using a ruler, the time duration of an event using a clock.
Quantities that cannot be measured using tools and instruments. For examples include love, affection, fear, wisdom, and beauty, which often pertain to the perception or interpretation of the observer.
Quantities selected arbitrarily by scientists to play a key role in describing physical phenomena. Base quantities are length, mass, time, temperature, electric current, etc.
Quantities that can be described in terms of one or more base quantities. For example, speed, area, volume, etc.
Measurement is a process of comparison of an unknown quantity with a widely accepted standard quantity.
The standard amount of a physical quantity, which is used to compare larger or smaller amounts, is called the unit.
The International System of Units (SI) is a system of measurement consisting of seven base units, recommended by the international committee on weights and measures in 1961.
Base units cannot be derived from one another and cannot be resolved into anything more basic.
Derived units are the units of quantities that can be expressed in terms of base units.
Prefixes are words or symbols added before SI units to express quantities as multiples or sub-multiples of base units using powers of 10.
Scientific notation is a method of representing very large or very small numbers in a compact form. It expresses numbers as a product of a number between 1 and 10, multiplied by a power of 10.
A metre rule is commonly used in laboratories to measure length. The smallest division on a metre rule is 1 mm, which is known as the least count of the metre rule.
Parallax error occurs due to the incorrect position of the eye when taking measurements. This results in inaccurate readings.
A measuring tape is used to measure lengths ranging from 1 mm to several metres. Its least count is 1 mm.
The Vernier Calliper is an instrument used to measure small lengths with high precision, down to 1/10 th of a millimetre.
The least count of a Vernier Calliper is the difference between one main scale division (1 mm) and one Vernier scale division (0.9 mm). Hence,
\[ \text{Least count} = 1 \text{ M.S div} - 1 \text{ V.S div} \] \[ = 1\,\text{mm} - 0.9\,\text{mm} \] \[ = 0.1\,\text{mm} \]
Zero error occurs if, on joining the jaws of Vernier Callipers, the zeros of the main scale and Vernier scale do not exactly coincide with each other. This error in the instrument is called zero error.
The zero of the Vernier scale is on the right side of the main scale zero.
The zero of the Vernier scale is on the left side of the main scale zero.
A screw gauge is an instrument used to measure very small lengths, such as the diameter of a wire or the thickness of a metal sheet.
The pitch of the screw gauge is the distance the spindle moves along the main scale when the thimble completes one full rotation.
The least count of a screw gauge is calculated using the formula:
\[ \text{Least Count} = \frac{\text{Pitch of the Screw Gauge}}{\text{Number of Divisions on the Circular Scale}} \] \[ \text{Least Count} = \frac{0.5\,\text{mm}}{50} \] \[ \text{Least Count} = 0.01\,\text{mm} \quad \text{or} \quad 0.001\,\text{cm} \]
The duration of an event is measured by a stopwatch, which contains two needles: one for seconds and one for minutes. The dial is divided into 30 big divisions, each further divided into 10 small divisions. Each small division represents \(\frac{1}{10}\) of a second, making \(\frac{1}{10}\,\text{s}\) the least count of the stopwatch.
A measuring cylinder is a cylinder made of glass or transparent plastic, with a scale marked in cubic centimeters (\(\text{cm}^3\) or cc) or milliliters (mL).
The meniscus is the curved surface of the liquid.
Significant figures (or digits) are the digits of a measurement that are reliably known. They include all the accurately known digits and the first doubtful digit, which is determined by estimation and has a probability of error.
Precision of a measurement refers to how close together a group of measurements are to each other.
Accuracy of a measurement refers to how close the measured value is to some accepted or true value.