Board of Intermediate and Secondary Education Rawalpindi Physics Notes for class 9th chapter 1 Physical quantities, Measurements Short, questions, Long, question, Mcqs, Video, and Problems Pdf Download New up to date Notes.
Physics Class 9th Notes Physical Quantities, Measurements Bise Rawalpindi
Mcqs
i) The number of base units in SI are:
- A. 3
- B. 6
- C. 7
- D. 9
ii) Which one of the following units is not a derived unit?
- A. Pascal
- B. Kilogram
- C. Newton
- D. Watt
iii) Amount of a substance in terms of numbers is measured in:
- A. Gram
- B. Kilogram
- C. Newton
- D. Mole
iv) An interval of 200 μs is equivalent to
- A. 0.2 s
- B. 0.02 s
- C. 2×10-4
- D. 2×10-6 s
v) Which one of the following is the smallest quantity?
- A. 0.01 g
- B. 2 mg
- C. 100 μ g
- D. 5000 ng
vi) Which instrument is most suitable to measure the internal diameter of a test tube?
- A. meter rule
- B. Vernier Callipers
- C. Measuring tap
- D. Screw gauge
vii) A student claimed the diameter of a wire as 1.032 cm using Vernier Callipers. Up to what extent do you agree with it?
- A. 1 cm
- B. 1.0 cm
- C. 1.03 cm
- D. 1.032 cm
viii) A measuring cylinder is used to measure:
- A. Mass
- B. Area
- C. Volume
- D. Level of a liquid
ix) A student noted the thickness of a glass sheet using a screw gauge. On the main scale, it reads 3 divisions while the 8th division on the circular scale coincides with the index line. Its thickness is:
- A. 3.8 cm
- B. 3.08 mm
- C. 3.8 mm
- D. 3.08 m
x) Significant figures in an expression are :
- A. all the digits
- B. all the accurately known digits
- C. all the accurately known digits and the first doubtful digit
- D. all the accurately known and all the doubtful digits
Short Questions
What is the difference between base quantities and derived quantities? Give three examples in each case.
Base quantities:
Base quantities are the quantities on the basis of which other quantities are expressed. There are seven physical quantities that form the foundation for other physical quantities.
Examples: Length, mass, time, electric current, temperature, the intensity of light, and the amount of substance.
Derived quantities
The quantities that are expressed in terms of base quantities are called derived quantities.
Examples: Speed, force, work, energy, power, electric potential, etc.
Find the base quantities involved in each of the following derived quantities:
a) speed
b) volume
c) force
d) work
Answer:
a) Speed:
v = S/t
unit of speed is ms-1
So base quantities involved in speed are length and time.
b) Volume
Volume = length x width x height
V = m x m x m = m3
So base quantity involved in volume is length.
c) Force:
F = ma
1 N = 1 kg x 1 ms-2
1 N = 1 kg ms-2
So base quantities involved in force are mass, length and time.
d) Work
W = FS
1 J = (1 N) (1 m)
1 J = (1 kg ms-2) (1 m)
1 J = 1 kg m2s-2
So base quantity involved in work are mass, length and time
Estimate your age in seconds.
Suppose my age = 15 years
=15 x 365 days (1 year = 365 days )
=15 x 365 x 24 hours (1 day = 24 hours)
=15 x 365 x 24 x 60 minutes (1 hour = 60 minutes)
=15 x 365 x 24 x 60 x seconds (1 minutes = 60 seconds)
= 473040000 seconds
What role SI units have played in the development of science?
SI system is used all over the world. Manipulation in this system is quite easy i.e the multiple and sub-multiple of different units are obtained simply by multiplying or dividing with ten or power of tens.
What do you understand by the zero error of a measuring instrument?
Zero error:
It is a defect in a measuring device (vernier caliper and screw gauge) and it is caused by an incorrect position of the zero point.
Example
To find the zero error, close the jaws of the vernier caliper gently. If the zero line of the vernier scale coincides with the zero of the main scale, the zero error is zero. Zero error will exist if the zero line of the vernier scale is not coinciding with the zero of the main scale.
Why is the use of zero error necessary in a measuring instrument?
When making some kind of scientific measurement, it is necessary to first check your measuring instrument for “zero error”. The zero error is the reading displayed when know the true reading should be exactly zero.
For example, using a set of vernier calipers, the zero error is the reading that shows when the calipers are fully closed.
When you check for zero error, you can use it to correct your readings.
Positive zero error:
Zero error will be positive if the zero line of the vernier scale is on the right side of the zero of the main scale.
To get the correct value, zero error must be recorded and subtracted from each reading.
Negative zero error:
Zero error will be negative if the zero line of the vernier scale is on the left side of the zero of the main scale.
To get the correct value, zero errors must be recorded and added from each reading.
What is a stopwatch? What is the least count of a mechanical stopwatch you have used in the laboratories?
STOPWATCH
A stopwatch is an instrument that is used to measure the time interval of an event.
MECHANICAL STOPWATCH
A mechanical stopwatch can measure a time interval up to a minimum of 0.1 seconds. The least count of a mechanical stopwatch is 0.1 seconds.
Why do we need to measure extremely small intervals of time?
We need an extremely small interval of time “delta t” (∆t) as the smaller the time interval, the better resolution of the measurement is possible.
For example, in atomic/quantum physics especially reactions take place in a very short amount of time.
What is meant by significant figures of a measurement?
All the accurately known digits and the first doubtful digit in an expression are called significant figures. It reflects the precision of a measured value of a physical quantity.
Non-zero digits are always significant. Thus, 22 has two significant digits, and 22.3 has three significant digits.
With zeroes, the situation is more complicated:
1) Zeroes placed before other digits are not significant; 0.046 has two significant digits.
2) Zeroes placed between other digits are always significant; 4009 kg has four significant digits.
3) Zeroes placed after other digits but on the right side of a decimal point are significant; 7.90 has three significant digits.
4) Zeroes at the end of a number are significant only if they are on the right side of a decimal point as in (3). Otherwise, it is impossible to tell if they are significant. For example, in the number 8200, it is not clear if the zeroes are significant or not. The number of significant digits in 8200 is at least two, but could be three or four. To avoid uncertainty, use scientific notation to place significant zeroes behind a decimal point:
How is precision related to the significant figures in a measuring instrument?
Greater the number of significant figures, the greater the precision. Each significant figures increase the precision by a factor of ten.
An improvement in the quality of measurement by using a better instrument increases the significant figures in the measured result. The significant figures are all the digits that are known accurately and the one estimated digit. The more significant figure means greater precision.
Problems
Q.1) Express the following quantities using prefixes.
i) 5000 g
ii) 2000 000 W
iii) 52×10-10 kg
iv) 225×10-8s
Answer:
i) 5000 g
=5×1000 g
=5×103 g
=5×1 kg (103 = 1 k)
=5 kg
ii) 2000,000 W
=2×1000000 W
=2×106 W
=2× 1 Mega W (106=1 Mega)
=2 MW
iii) 52×10-10 kg
=5.2×101×10-10 kg
=5.2×10-9 kg
=5.2×10-9 ×1000 g
=5.2×10-9 ×103 g
=5.2×10-6g
=5.2×1 Micro g (10-6=1 Micro)
=5.2 µg
iv) 225×10-8s
=2.25×100×10-8 s
=2.25×102×10-8 s
=2.25×10-6 s
=2.25×1 Micro s (10-6=1 Micro)
=2.25 µs
Q.2) How do the prefixes micro, nano and pico relate to each other?
Answer:
As we know
Micro; µ = 10-6
Nano; n = 10-9
Pico; p = 10-12
The relations between micro, nano and pico can be written as;
µ = 10-6
n = 10-9 = 10-3×10-6 = 10-3 µ
p = 10-12 = 10-6×10-6 = 10-6 µ
Q.4) Rewrite the following in standard form.
i) 1168×10-27
ii) 32×10 5
iii) 725×10-5 kg
iv) 0.02×10 -8
Answer:
i) 1168×10-27
=1.168×103×10-27
=1.168×10-24
ii) 32×105
=3.2×101×105
=3.2×106
iii) 725×10-5 kg
=7.25×102×10-5 ×103g (k=103)
=7.25 g
iv) 0.02×10-8
=2×10-2×10-8
=2×10-10
Q.8) Which of the following quantities have three have significant figures.
i) 3.0066m
ii) 0.00309 kg
iii) 5.05×10-27kg
iv) 301.0 s
Answer:
i) 3.0066 m
Zeros between significant digits are significant. Therefore there are 5 significant figures in 3.0066 m.
ii) 0.00309 kg
Zeros used for spacing the decimal point are not significant. Therefore there are 3 significant figures in 0.00309 kg.
iii) 5.05 × 10-27 kg
Only the digits before the exponent are considered. Thus, there are 3 significant figures.
iv) 301.0 s
Zeros after the decimal are significant so there are 4 significant figures.
So (b) and (c) have 3 significant figures.
Q.9) What are the significant figures in the following measurements?
i) 1.009 m
ii) 0.00450 kg
iii) 1.66×10-27 kg
iv) 2001 s
Answer:
i) 1.009 m
Zeros between significant digits are significant. Therefore there are 4 significant
figures.
ii) 0.00450
Zeros used for spacing the decimal point are not significant. Therefore there are 3 significant figures
iii) 1.66×10-27
Only the digits before the exponent are considered. Thus, there are 3 significant figures.
iv) 2001 s
Zeros between significant digits are significant. Therefore there are 4 significant figures.
Q.10) A chocolate wrapper is 6.7 cm long and 5.4 cm wide. calculate its area up to a reasonable number of significant figures.
Answer:
Length of chocolate wrapper; l = 6.7 cm
Width of chocolate wrapper; w = 5.4 cm
Area =?
Area = Length × width
A = l × w
A = 6.7 × 5.4 = 36.18 cm2
A ≈ 36 cm2
Solved Past Papers Matric (Science with Biology) Rawalpindi Board |Grade 9
i) The boiling point of lead is:
A. 1750oC
B. 175oC
C. 170oC
D. 750oC
Answer:
A. 1750oC
ii) The major source of heat Energy is:
A. Earth
B. Moon
C. Centaurus
D. Sun
Answer:
D. Sun
iii) The number of base units in SI is:
A. None
B. 6
C. 7
D. 8
Answer:
C. 7
iv) The unit of velocity is:
A. ms-2
B. ms-1
C. ms1
D. ms2
Answer:
B. ms-1
v) The formula of Newton’s second law of motion is:
A. P = mv
B. F = ma
C. W = mg
D. F = kx
Answer:
B. F = ma
vi) The formula of centripetal acceleration is:
A. ac =v/r
B. ac =v2/r2
C. ac =v/r2
D. ac =v2/r
Answer:
D. ac =v2/r
vii) The unit of torque is:
A. N.m
B. N.m2
C. N.m-2
D. N.m-1
Answer:
A. N.m
viii) The formula for the mass of the earth is:
A. Me = Rg/G
B. Me = R2g/G2
C. Me = R2g/G
D. Me = R2g2/G
Answer:
C. Me = R2g/G
ix) One joule is equal to:
A. 1J=1N
B. 1J=1N.1m
C. 1J=1N.1A
D. 1J=1N.1m2
Answer:
B. 1J=1N.1m
x) Mass-energy equation is:
A. E=mc2
B. E=mc
C. E=½mv2
D. E=m2c2
Answer:
A. E = mc2
xi) The unit of density is:
A. Kg.m3
B. Kg.m-3
C. Kg.m-2
D. Kg.m2
Answer:
B. Kg.m-3
xii) The formula of specific heat is:
A. c= ΔQmΔt
B. c= ΔQm/Δt
C. c= ΔQm
D. c= ΔQ/mΔt
Answer:
D. c= ΔQ/mΔt
Q.2 i) Define base quantities and derived quantities.
Answer:
Base quantities:
There are seven physical quantities that form the foundation for other physical quantities. These physical quantities are called the base quantities. These are length, mass, time, electric current, temperature, the intensity of light, and the amount of a substance.
Derived quantities:
Those physical quantities which are expressed in terms of base quantities are called the derived quantities. These include area, volume, speed, force, work, energy, power, electric charge, electric potential, etc.
Q.2 ii) Write two rules to find the significant digits in a measurement.
Answer:
Two rules to find the significant digits:
- Digits other than zero are always significant. I.e
27 has 2 significant digits. 275 has 3 significant digits. - Zeros between significant digits are also significant. I.e
2705 has 4 significant digits.
Q.2 iii) Define scientific notation and give an example.
Answer:
Scientific Notation:
A way to express a given number as a number between 1 and 10 multiplied by 10 having an appropriate power is called scientific notation or standard form.
Example:
A number 62750 can be expressed as 62.75 × 103 or 6.275 × 104 or 0.6275 × 105.
Q.2 iv) Differentiate between distance and displacement.
Answer:
Distance:
Length of a path between two points is called the distance between those points.
It is a scalar quantity and can be completely described using only its magnitude.
Displacement:
Displacement is the shortest distance between two points which has magnitude and direction.
It is a vector quantity and it requires both direction and magnitude to completely describe it.
Q.2 v) Differentiate between speed and velocity.
Answer:
Speed:
The distance covered by an object in unit time is called its speed.
Mathematically:
Speed = Distance/Time
v = S/t
It is a scalar quantity and can be completely described using only its magnitude.
Velocity:
The rate of displacement of a body is called its velocity.
Mathematically:
Velocity = Displacement/Time
v = d/t
It is a vector quantity and it requires both direction and magnitude to completely describe it.
Q.2 vi) Define momentum and write its S.I unit.
Answer:
Momentum:
Momentum of a body is the quantity of motion it possesses due to its mass and velocity. The momentum P of a body is given by the product of its mass m and velocity v.
Mathematically:
P = mv
SI Unit:
The SI unit of momentum is kgms-1 .
Q.2 vii) Define friction and limit friction.
Answer:
Friction:
The force that opposes the motion of moving objects is called friction.
Limiting Friction :
Friction is equal to the applied force that tends to move a body at rest. It increases with the applied force. Friction can be increased to a certain maximum value. It does not increase beyond this. The maximum value of friction is known as the force of limiting friction (Fs).
Q.2 viii) Define Atwood machine and write its one use.
Answer:
Atwood Machine:
An Atwood machine is an arrangement of two objects of unequal masses. Both the objects are attached to the ends of a string. The string passes over a frictionless pulley.
Use:
It is used to find the acceleration due to gravity.
Q.3 i) State principle of moments.
Answer:
Principle of Moments:
It is stated as, “A body is balanced if the sum of clockwise moments acting on the body is equal to the sum of anticlockwise moments acting on it.”
Q.3 ii) What is meant by the center of gravity?
Answer:
Center of gravity:
A point where the whole weight of the body appears to act vertically downward is called the center of gravity of a body .
Q.3 iii) What are artificial satellites?
Answer:
Artificial satellites:
Scientists have sent many objects into space. Some of these objects revolve around the Earth. These are called artificial satellites.
Q.3 vi) Define energy & write two types of mechanical energy.
Answer:
Energy:
The capability of an object to do work is called energy.
Type of Mechanical Energy:
- Kinetic Energy
- Potential Energy
Q.3 vii) What is the value of speed of light?
Answer:
Speed of Light:
The speed of light is 3 × 108 ms-1.
Q.3 viii) Define power and write its S.I unit.
Answer:
Power:
Power is defined as the rate of doing work.
Mathematically:
Power = Work/t
P = W/t
Unit:
SI unit of power is watt (W).
Q.4 i) Define stress and strain and write their units.
Answer:
Stress:
The force acting on the unit area at the surface of a body is called stress.
Mathematically:
Stress = Force/Area
Stress = F/A
Units:
In SI, the unit of stress is newton per square meter,(Nm-2)
Strain:
When stress acts on a body, it may change its length, volume, or shape. A ratio of such a change caused by the stress with the original length, volume or shape is called a strain.
Mathematically:
Strain = Change in length/Original length
Units:
Strain is the ratio of two same quantities so it has no unit.
Q.4 ii) Define Young’s modulus.
Answer:
Young’s Modulus:
It is defined as,
“The ratio of stress to tensile strain is called Young’s modulus.”
Mathematically:
Young’s Modulus = Stress/Tensile Strain
Y = Stress/Tensile Strain
Where,
Stress = F/A, and Strain = ΔL/L.
Hence,
Y = (F/A)/(ΔL/L)
or
Y = FL/AΔL
Units:
SI unit of Young’s modulus is a newton per square meter (Nm-2)
Q.4 iii) Why does the atmospheric pressure vary with height?
Answer:
The atmospheric pressure decreases as we go up because the density of air decreases as we go up. The decreases in density mean there is a lesser number of air molecules present in the atmosphere at height and hence they exert less force. So, as a result, the atmospheric pressure decreases.
Q.4 iv) What is meant by bimetallic strip?
Answer:
Bimetallic Strip:
A bimetal strip consists of two thin strips of different metals such as brass and iron joined together. On heating the strip, brass expands more than iron. This unequal expansion causes bending of the strip.
Bimetal thermometers are used to measure temperatures, especially in furnaces and ovens. They are also used in thermostats.
Q.4 v) How does heat affect the motion of molecules of a gas?
Answer:
Temperature is directly proportional to kinetic energy. It means that the larger the temperature of a gas, the faster the molecules will move. Due to this reason, when heat increases in a system, the motion of the molecules also increases.
Q.4 vi) Why is a double-walled glass vessel used in thermos flask?
Answer:
The double-walled glass flask has a vacuum between the two layers of glass. This effectively isolates the contents of the flask from the environment around. That’s why anything placed in the flask maintains its coldness or hotness for a long time.
Q.4 vii) How does heat reach us from the sun?
Answer:
From the sun, heat is transferred to the earth by the method of radiation. The other methods like convection and conduction are not possible due to the vacuum in the large region between the sun and earth.
Q.4 viii) Explain the impact of the greenhouse effect on global warming?
Answer:
The greenhouse effect keeps the temperature of the earth moderate by trapping heat. But due to human activity, the emission of greenhouse gasses (carbon dioxide, methane, nitrous oxide) from factories is increasing alarmingly. Plants convert carbon dioxide to oxygen but due to deforestation, the amount of carbon dioxide in the atmosphere is increasing and the balance of nature is being disrupted. As a result, the temperature of the earth is steadily rising adding to global warming. This, in turn, is affecting the pattern of rains, melting rate of glaciers and rise in the level of seas. If it remains unchecked, the increase in global warming due to ever-increasing human activities will drastically affect the future of this planet.
Q.5 b) A body of 5 Kg is moving with a velocity of 10ms-1 Find the force required to stop it in 2 Seconds.
Answer:
Given data:
Mass = m = 5 kg
Initial velocity = vi = 10ms-1
Final velocity = vf = 0
time = t = 2s
To find:
Force = F = ?
Calculation
Using the definition of momentum
Pi = movie
Pi = (5)(10)
Pi = 50 Ns
Pf = mvf
Pf = (5)(0)
Pf = 0
Since
F = (Pf – Pi)/t
F = (50 – 0)/2
F = 50/2
F = 25 N
Q.6 a) Define kinetic energy and derive its formula.
KE = 1/2 mv2
Answer:
Definition :
” The energy possessed by a body due to its motion. “
Proof of K.E = ½mv2:
Consider a body of mass ‘m’ placed on a horizontal surface initially at rest. When a force ‘F’ is applied, it covers a distance ‘S’ and its final velocity becomes “v”. Work done is covering the displacement S.
W = F.S …………………… (i)
But by the second law of motion, when a force acts on a body, it produces an acceleration in the direction of a force.
F = ma …………………… (ii)
And by using equation of motion, i.e.
vf2 – vi2 = 2aS
When vi = 0, vf = v, S = ?
∴ v2 – 0 = 2aS
or
S = v2/2 a ………………. (iii)
Putting the value of ‘F’ and ‘S’ in equation (i)
Work = K.E = F.S = ma × v2/2a
∴ K.E = mv2/2 = ½mv2
K.E = ½mv2
Q.6 b) A mechanic tightened the nut of a bicycle using a 15cm long spanner by exerting a force of 200N. Find the torque that has tightened it.
Answer:
Given data:
Moment arm = r = 15cm = 0.15m
Force = F = 200N
To find:
Torque = τ = ?
Calculation:
The torque is given by,
τ = F×r
τ = (200)×(.15)
τ = 30 Nm
Q.7 a) Define specific heat. How would you find the specific heat of a solid?
Answer:
Specific Heat:
The specific heat of a substance is defined as,
“Specific heat of a substance is the amount of the heat required to raise the temperature of 1 kg mass of that substance through 1K.”
Specific Heat of a Solid:
Specific heat of a solid can be calculated by the formula
△Q = c m △T
or
c = △Q/m △T
Where △Q is the amount of heat absorbed, c is the specific heat capacity of solid, m is the mass of the solid and △T is the change in temperature.
The Specific heat is measured in a unit Jkg-1K-1.
Q.7 b) A wooden block measuring 40cm × 10cm ×5cm has a mass 850g. Find the density of the wood.
Answer:
Given data:
Mass = m = 850g = 0.85kg
Length of 1st side = l1 = 40cm = 0.40m
Length of 2nd side = l2 = 10cm = .10m
Length of 3rd side = l3 = 5cm = 0.05m
To find:
Density = d = ?
Calculation:
The volume can be calculated as
V = l1×l2×l3
V = 0.40 × 0.10 × 0.05
V = 2 × 10-3 m3
Now
The density is given by
d = m/V
d = 0.85/2 × 10-3
d = 425 kgm3
