9th physics chapter:1 Physical quantities and measurement

Q1. How technology shaped by physics?

Technology shaped by physics in many ways

Technology	Physics
Steam engine	Laws of thermodynamics
Nuclear reactor	Controlled nuclear fission
Radio and Television	Generation, propagation and detection of electromagnetic waves
Computers	Digital logic gates
Rocket propulsion	Newton’s laws of motion
Sonar	Reflection of ultrasonic waves
Optical fibers	Total internal reflection of light
Non-reflecting coatings	Thin film optical interference
Electron microscope	Wave nature of electrons
Photocell	Photoelectric effect

Q2.Physics and biology are considered different branches of science, how physics links with biology?

Physics has many applications in the biological sciences.

•         i.            On the microscopic level, it helps describe the properties of cell walls and cell membranes.
•       ii.            On the macroscopic level, it can explain the heat, work, and power associated with the human body.
•     iii.            Physics is involved in medical diagnostics, such as x-rays, magnetic resonance imaging (MRI), and CT scan etc.
•     iv.            Medical therapy sometimes directly involves physics; for example, cancer radiotherapy uses ionizing radiation.
•       v.            Physics can also explain sensory phenomena, how we hear sound, how the eye detects color.

Q3.Why are measurements important?

Measurement is important because:

•    i.            Measurement is an integral part of human race, without it there will be no trade, no statistics. 
•       ii.            Kids try to compare their height, size of candy, size of dolls and amount of toys they have.
•     iii.            We measure distances between different cities.
•     iv.            We measure values in different experiments.
•       v.            To buy or sell clothes and food items we measure.

Q4.Why area is called a derived quantity?

Area is the multiplication of two base physical quantities length and width. Therefore it is known as derived physical quantity.

Mathematically

Area = length x width

A = Lx W

The SI unit of area is m².

Q5.Name any four derived units and write them as their base units?

Name of any four derived units and write them as their base units are:

S.no.	Derived unit	Base unit
I.	Square meter	m2(m.m)
II.	newton	kgms-1
III.	Cubic meter	m3(m.m.m)
IV.	joule	kgm2s-2
V.	Meter per second	m/s

Q6.Why in physics we need to write in scientific notation?

In Science one often needs to work with very large or very small numbers. These can be written more easily in scientific notation or standard form. Generally

N=M x 10ⁿ

Here N=number

M=mantissa

n= exponent

Q7.What is least count? How least count for Vernier caliper and screw gauge are defined?

The minimum length that can be measured by an instrument is called least count (L.C)

Least count for Vernier calipers

The smallest digit on the main scale divided by the total numbers on the Vernier scale is called least count of Vernier calipers. Mathematically

L.C=1mm/10 = 0.1mm or 0.01cm

Least count for screw gauge

The pitch of the screw divided by the total number of divisions on the circular scale is called least count of the screw gauge. Mathematically

L.C=1mm/100 = 0.01mm or 0.001cm

Q8.How can we find the volume of a small pebble with the help of measuring cylinder?

We can find the volume of a small pebble when water is poured in measuring cylinder and noted the volume of water V1. Then put the pebble in the cylinder gently. When the pebble is completely immersed the volume of water is read again as V₂. The volume of the pebble (∆V) is found by subtracting the first reading V₁ from the second V₂.

∆V= V₂ - V₁