Q.1 what is science? Also write its two streams. Science: “The knowledge that gains through observation and experimentation is called science.” There are two main stream in which science is divided. (i) Physical Sciences (ii) Biological Science

1. October 20, 2018 [PREPARED BY AHSAN MEHMOOD]
Physics 9th class
Unit: 01 “Physical Quantities
and Measurements”
Q.1 what is science? Also write its two streams.
Science:
“The knowledge that gains through observation and
experimentation is called science.”
There are two main stream in which science is divided.
(i) Physical Sciences (ii) Biological Science
Q.2 what is difference between physical sciences and biological
sciences?
Physical Sciences Biological science
The study of non-living things is
known as physical sciences.
e.g. Physics, Chemistry &
Mathematics.
The study of living things is called
biological sciences.
e.g. Biology, zoology and Botany.
Q.3 write the names of branches of Physics. Also define each
branch.
Ans. Mechanics:
The branch of physics which is study of motion of object, its causes
and effects.
e.g. Motion of Fan, cart is moving, buss is taking turn etc.
Geo Physics:
Geo means earth. The branch of physics that deals with the study of
internal structure of earth.
e.g. Study of seismic waves, earth quacks and day & nights etc.
Atomic Physics:
It is the study of atom, the structure of atom and properties of
atoms.

2. October 20, 2018 [PREPARED BY AHSAN MEHMOOD]
e.g. study of isotopes, reactions of atoms and occurrence of atom in
the universe etc.
Heat Physics:
It is study of nature of heat, heat always travel from hot to cold
bodies and effects of heat.
e.g. temperature and heat, thermometer, expansion of matter due
to heat etc.
Sound Physics:
The branch of physics that deals with the study of
production of sound, its physical aspects and properties of sound.
e.g. we speak our language, noise and music are studied in sound
physics.
Light Physics:
It is the study of nature of light, its physical aspects,
properties and physical aspects of sound.
e.g. in our surrounding we see many object this is due to light, so we
study working of light in our daily life.
Nuclear Physics:
It is the study of properties of nucleus and behavior of
nucleus of an atom.
e.g. It is also study of particles present in nucleus like proton,
neutrons and many other subatomic particles.
Electricity and magnetism:

3. October 20, 2018 [PREPARED BY AHSAN MEHMOOD]
Effect of charges in motion is called electricity
and charges in motion has magnetic field around them. The relation
of electricity and magnetism is studied in electricity and magnetism.
Plasma Physics:
It is study of production of ionic state of matter which
fourth state of motion.
e.g. we have plasma in tube lights, siren and in sun.
Q.4 why do we study physics?
Ans. We study physics because it involves in our everyday life. We sit
this is physics, we speak this is physics, we walk this is physics.
Q.5 what are physical quantities?
Ans. The quantities which can be measure are called physical
quantities.
e.g. Mass, Length, time, electric current temperature etc.
Q.6 How many types of Physical quantities?
Ans. There are two types of physical quantities.
(i) Base Quantities.
(ii) Derive Quantities
Q.7 what is difference between Base quantities and derive
quantities?
Base Quantities Derive Quantities
The quantities on which other
quantities are expressed are
called Base quantities.
They are seven in number.
e.g. Length, mass, time, electric
The quantities which are derive
on the basis of base quantities
are called derive quantities.
There are many derive quantities.
e.g. speed, acceleration, volume,

4. October 20, 2018 [PREPARED BY AHSAN MEHMOOD]
current, intensity of light,
temperature and amount of
substance.
work, force, pressure, electric
charge etc.
Q.8 Define base units and derive units?
Base Units:
The units of base quantities are called base units.
E.g. length has its unit meter, time has its unit second etc.
Derive Units:
The units of derive quantities are called derive units.
E.g. speed has its unit meter per second per second; volume has its
unit cubic meter.
Q.9 what do you know about prefixes?
Ans. The words or letters that are added before SI units are called
prefixes.
e.g. Kilo, Mega, Milli, Centi, Micro etc.
Distance between school and Ali’s home is 1 km. where 1 is
magnitude, kilo (k) is prefix and meter (m) is unit.
Important Points:
i. Prefixes are always use before SI unit.
ii. Double prefixes cannot be use.
Q.10 what is scientific notation?
Ans. When a large number is expressed in its multiples and sub-
multiples and then multiply by a number between 1 and 10 is called
scientific notation.

5. October 20, 2018 [PREPARED BY AHSAN MEHMOOD]
e.g. A number 62750 can be expressed as 62.750 x 103
or 0.62750 x
105
. All these are correct.
Important Points:
i. The number that has one non-zero digit before decimal i.e.
6.257 x104
is taken as standard form.
ii. Similarly standard form of 0.00045 is 4.5 x 10-4
.
Q.11 The sun is one hundred and fifty million kilometers away from
the earth. Write its ordinary and scientific notation.
Ans. As we know that 1 million is equal to 10 lakh, so 150 million is
equal to 1500 lakh.
The ordinary notation is 150000000.
The scientific notation is 1.5x108
.
Q.12 what do you know about meter rule?
Ans. The device which is used to measure the length of an object
through 1m is called meter rule.
Important points:
i. Its length is 1 meter.
ii. Its 1m is divided into 10 cm.
iii. Its 1 cm is divided into 10 mm.
iv. Its least count is 1mm.
Q.13 what is least count? Write least count of some devices.
The smallest value which can be measure by an instrument
accurately is called least count (L.C) of that device.
Least Count (L.C) =
Smallest division or pitch of main scale
Total division on vernier or circular scale

6. October 20, 2018 [PREPARED BY AHSAN MEHMOOD]
Least counts of some devices:
1) Meter rule has its least count 1mm.
2) Vernier caliper has its least count 0.1mm.
3) Screw gauge has its least count 0.01mm.
4) Beam Balance has its least count 0.1g
5) Physical balance has its least count 0.01g
6) Electronic balance has its least count 0.001g
7) Mechanical stopwatch has its least count 0.1s
8) Digital stopwatch has its least count 0.01s.
9) Digital vernier caliper has its least count is 0.01mm.
Q.14 why digital vernier caliper has greater precision then
mechanical vernier caliper?
Ans: Digital vernier caliper has its least count (L.C) 0.01mm while the
mechanical vernier caliper has its least count (L.C) 0.1mm. The device
with smallest least count has greater precision. So digital vernier
caliper is more precise as compare to mechanical vernier caliper.
Q.15 what do you know about zero error of vernier caliper?
Ans. On closing the jaws of vernier caliper, if the zero line of vernier
scale does not coincide with the zero line of main scale. This error in
zero is called zero error.
Important point:
i. If zero line of vernier scale lie on the left side of zero of main
scale then it will consider as negative zero error. It will be
added in final reading for zero error correction.
ii. If zero line of vernier scale lie on the right side of zero of main
scale then it will consider as positive zero error. It will be
subtracted from final reading for zero error correction.

7. October 20, 2018 [PREPARED BY AHSAN MEHMOOD]
Q.16 what is difference between vernier caliper and screw gauge?
Vernier Caliper Screw gauge
1. The device which can
measure 0.1 mm accurately
is known as vernier caliper.
2. Its least count (L.C) is 0.1
mm.
3. It has two scales one main
scale (Fixed) and other is
vernier scale (Moveable).
4. It can find external
diameter of cylinder as well
as internal diameter of
cylinder.
5. Vernier caliper is less
precise then screw gauge
because it has greater least
count then screw gauge.
1. The device which can
measure 0.01 mm
accurately is known as
screw gauge.
2. Its least count (L.C) is
0.01mm.
3. It has two scales one is
main scale (fixed) and other
is circular scale (Moveable).
4. It can only used to find
external diameter of
cylinder.
5. Screw gauge is more precise
then vernier caliper
because it has smaller least
count (L.C) then vernier
caliper.
Q.16 How do you measure the volume of irregular shaped solid?
Ans. We can use measuring cylinder to find the volume of irregular
shaped cylinder. Take some water in the measuring cylinder. Note
the volume of water which Vi (initial volume). Take a irregular shaped
stone and lower the solid till it fully immersed in water. Then note
the volume which Vf. Now to find the exact volume Vf – Vi.
Q.17 what is vernier Constant?
Ans. The ratio of smallest divisions of main scale to the total divisions
of vernier scale is called vernier constant.
Least Count (L.C) =
Smallest division or pitch of main scale
Total division on vernier or circular scale
Q.18 write a note on screw gauge.

8. October 20, 2018 [PREPARED BY AHSAN MEHMOOD]
Ans.The screw gauge is an instrument used for measuring accurately
the diameter of a thin wire or the thickness of a sheet of metal. It
consists of a U-shaped frame fitted with a screwed spindle which is
attached to a thimble. The pitch of the screw is the distance moved
by the spindle per revolution
Q.19 what are significant figures? Write down rule for counting
significant figures.
Ans. All accurately known digits and first doubtful digit in an
expression is called significant figures.
Rules for Counting Significant Figures:
I. All non-zero digits are called significant figures.
II. The zero between two significant figures is also significant.
III. The zero on left side of significant figures is not significant.
IV. The zero on right side of decimal point is also significant.
V. The zero on the right side of significant is not significant if
decimal point is not present.