# 9th Class Physics: Chapter 1 Physical Quantities and Measurement Short Questions with Answers

## 9th Class Physics: Chapter 1 Physical Quantities and Measurement Short Question Answers

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Base quantities are the quantities on the basis of which other quantities are expressed. Length, mass, time, eclectic current, temperature, intensity of light and amount of substance are examples of base quantities.

Derived quantities:

The quantities that are expressed in term of base quantities are called derived quantities. Volume, speed, force, work, energy, power and electric charge are some examples of driveled quantities.

Joule, Newton, kilogramme, hertz, mole, ampere, meter, Kelvin, coulomb and watt

Speed:

The formula of speed is:

Speed = distance covered by body/time taken

Unit of Speed:

Speed = meter/second = ms-1

Unit of speed shows that speed is a derived quantity and it is derived from length and time. Meter is the unit of length and second is the unit of time.

Length and time are base quantities.

(b) Volume:

The formula of volume is:

Volume = Length x width x height

Unit of Volume:

Volume = meter x meter x meter

=m3

The Unit of volume shows that volume is derived quantity and is obtained from the length.

Length is a base quantity and its unit is meter.

(c) Force:

The formula of force is:

Force = mass x acceleration

F = m x a

Unit of force:

Force = kiogramme x meter per second per second

= kg ms-2

The Unit of mass is kilogramme, the unit of length is meter and the unit of time is second.

The unit if force shows that mass, length and time. Mass, length and time are base quantities

(d) Work:

The formula of work is:

Work = F x S

Unit of Work:

Work = kgms2 x m

= kgms2 s-2

Unit of work shows that it is a derived quantity. Work is derived from the mass length and time.

Mass, length and time are base quantities.

Answer: Supposed age of a person = 15 years.

Total days in one year = 365 days

Total days in 15 year = 365 x 15 = 5475 days

Total hours in one day = 24 hours

Total hours in 5475 days = 5475 x 24 = 131, 400 hours

Total minutes in one hours = 60 minutes

Total minutes in 131, 400 hours = 131, 400 x 60 = 7884000 minutes

Total seconds in one minutes = 60 seconds

Total seconds in 7884000 minutes = 7884000 x 60

15 years of age = 473, 040, 000 seconds

By the given method you can convert your exact age into seconds.

SI units have played a very important role in the development of science.

SI units are very helpful to exchange scientific and technical information at the international level.

The least count of the vernier calipers is also called the vernier constant. It can be defined as:

The difference between one small division on main scale division and one vernier scale division is 0.1 mm. It is called least count (LC) of the vernier calipers.

Least count of the vernier calipers can also be found as given below.

Least count of vernier calipers = Smallest reading on the main scale/Number of division on vernier scale

By closing the jaws of measuring device, if the zero line of one scale (vernier scale) coincides with the zero line of its main scale (other scale) then there is no zero error. But zero error will exist if the zero line of one scale (vernier scale) is not coinciding with the zero of other scale (main scale). Zero error will be positive if zero line of one scale (vernier scale) is on the right side of the zero of other scale (main scale) and will be negative if zero line of one scale (vernier scale) is on the left side of zero of the other scale(main scale).

Zero error is necessary in measuring instrument to obtain an extreme correct value.

Stopwatch is a device which is used to measure the time interval of an event. Mechanical stopwatch have least count upto 0.1 second.

In nature and also in physics, there are so many phenomenons which vary with respect to the extremely small interval of time and fir their experimental measurement we need very precise time measuring instrument. We need to measure extremely small interval of times to calculate the time interval of natural and artificial events.

All the accurately known digits and first doubtful digits in as expression are called significant figures.

Significant figure reflects the precision of a measured value of physical quantity.

An improvement in the quality of measurement by using better instrument increases the significant figures in the measured results. The significant figures are all the digits are known accurately and the one estimated digit.

More significant figure means greater precision.

Physics is the branch of science in which matter, energy and their interaction are studied.

Plasma Physics: It is the study of production, properties of ionic state of matter-the fourth state of matter.

Geo physics: It is the study of the internal structure of the Earth.

Atomic physics: It is the study of the structure and properties.

Plasma Physics: It is the study of production, properties of ionic state of matter-the fourth state of matter.

It is the study of the charges at rest and in motion, their effects and their relationship with magnetism.

Atomic Physics: It is the study of the structure and properties of atoms.

Nuclear Physics: It deals with the properties and behaviour of nuclei and the particles within the nuclei.

Mechanics: This branch of physics is the study of motion of objects, its causes and effect.

Geophysics: It is the study of the internal structure of the Earth.

Mechanics: This branch of physics is the study of motion of objects, its causes and effect.

Electromagnetism: It is the study of the charges at rest and in motion, their effects and their relationship with magnetism.

A car is made on the principles of mechanics.

A refrigerator is based on the principle of thermodynamics.

Base Quantities: Base quantities are the quantities on the basis of which other quantities are expressed.

Length, mass, time, eclectic current, temperature, intensity of light and amount of substance are examples of base quantities.

Derived quantities: The quantities that are expressed in term of base quantities are called derived quantities.

Volume, speed, force, work, energy, power and electric charge are some examples of driveled quantities.

Length and Mass

The units used to measure derived quantities are called derived units. OR derived units are defined in term of base units and are obtained by multiplying or dividing one or more base units with each other.

The eleventh General Conference on Weight and Measures held in Paris in 1960 adopted a world-wide system of measurement called, International System of Units.

The International System of Units is commonly referred as SI.

Base quantities: Base quantities are the quantities on the basis of which other quantities are expressed.

There are seven physical quantities which form the foundation for other physical quantities. These physical quantities are called the base quantities.

Base Units: The units that describe base quantities are called base units. Each base quantity has its SI units.

Speed, acceleration, volume, force

Prefixes are the words or letters added before a unit and stand for the multiples or sub-multiples of that unit. For example, kilo, mega, milli, micro etc.

15 years = age

One year = 12 months

One year = 365 days

One year = 8760 hours

One year = 525, 600 minutes

One year = 525, 600 x 60 = 31, 536, 000 sec

15 year = 15 x 315, 36000 sec

15 years = 473, 040, 000 sec

Express in scientific notation: 0.00580 km, 210.0 g

0.00580 km = 5.80 x 10-3

210.0 g = 2.1 x 102 g

In Physics, scientific notation saves writing down or interpreting large numbers of zeros.

0.00580 km = 5.80 x 10-3

100.8 sec = 1.008 x 102 sec

Zero Error: If the zero of the main scale does not coincide with the zero of the vernier scale, when the jaws closed there is zero error in the instrument.

Zero correction: To remove the error in the instrument in called zero correction.

The instrument, screw gauge is more precise than vernier calipers because the least count of vernier calliper is 0.01 cm while the least count of screw gauge is 0.001 cm.

The stopwatch starts when the knob is pressed one. When pressed second time, it stops the watch while the third press bring the needle back to zero position.

Meter rod: A meter rule is a length measuring instrument.

Least count: One millimeter in the smallest reading that can be taken using a metre rule and is called its least count.

The smallest reading that can be measured from any instrument is called least count.

The least count of meter rod is 1mm.

A physical balance is used in the laboratory to measure the mass of various objects by comparison.

1.35 rounded to 1.4 and 1.45 rounded to 1.4

Mechanical Stop Watch: A mechanical stopwatch can measure a time interval up to minimum 0.1 second.

Digital Stopwatch: Digital stopwatch is commonly used in laboratories can measure a time interval as small as 1/100 second or 0.01 second.

Least count of screw gauge: Least count of screw gauge can be found as given below.

Least count = Pitch/Number of divisions on circular scale

Least count = 1mm/100 = 0.01 mm

Least count = 0.01 mm = 0.001 cm

Least count of the screw gauge is 0.01mm or 0.001 cm.

All the accurately known digits and first doubtful digits in as expression are called significant figures.

Significant figure reflects the precision of a measured value of a physical quantity. In 0.027, there are two significant figures.

1. Non-zero digits are always significant.

2. Zero between two significant figures is also significant.