Bridgecourse Physics Arihant for self study after class 10 Boards Part 2 From page 269 till end 560 Vikas Jain IIT JEE Engineering Medical Foundation KVPY Olympiad

293 Pages·2018·73.56 MB·English

by  Vikas Jain

bridgecourse

Physi
bridgecourse

Physics

A Self Study Course after
Class 10 Board Exams

to Bridge the gap between Class X & XI 8
to Build Foundation for Engineering/Medical Entrances

Vikas Jain

>«arihant

ARIHANT PRAKASHAN (SERIES), MEERUT
PREFACE

xing involved in preparing the students fo JE forthe last many yeas personaly elt that when
students enter in das th they felt of ty a malting ther spt and enthusiasm of
High Schoo The reason beng that theresa vast gap between thelevels ofthe to cases, Almost
‘rerything taught to them 1° casi ether new to them or hasbeen aughtto them na
ferent manner. Moreover, the ast labus andthe big ft books fightened ther, asa rest of
‘which even the very bight students of Highschool tet oe the coiidence nthe ii ste
‘of thirintermediate There are many good books aval inthe market which serves the purpose
forcuriculum of classes 10° nd 1b there en bok valble the market which an bide
the gap ofthese two dases ndhep the High schoo students to become successful student in
‘eb intermedi 0

‘Tebookin your hand wren wth he mott>"Maintain the pace and split four young minds
{or Towards JE. The ies behind the iteduction of ths products of Me Deepesh an (Oectr,
‘Athan Patashan) With ths met i ind completely went rough the slabs of ass 6,9",
10 and ted to varus ploneer teachers of High School and thor vein nF foundation|
program about ther curiam level of stdent and teaching methodologies, Wh ths smal
‘eseurch started to develop the content of Towa JE

‘The major problem wha faced shat upto High choo Alea based phys hasbeen aught
andi 1" ls calcu bated, moreover he stunts camo know the things abou calc n
the 2 ea ofthelrintermediate, soto develop the content ofthis bok eat ue calcul andes
sleoa proven fot that without acl ts very fit explain certain concepts np ll
ted to epiin those concepsina diferent ay by taking ceraln examples om lye or
Shipped tore concepts To understand the content ofthis book ou donot ned any previous
Concepts of physics. The books complet nallense. The ol thing wich ee requ the
ti receptive mind ciroatyto lean hablo understand the things om core and te
mathematical sil.

“Thisbook canbe wel for students of 8 9 and 10" cas ot for 10 to 17" moving students of by
thote whe are having erin physi oF nt having any Interest in phys. THs book wily tokeep
youlniace forse

‘have putin my best sincere forts to develop the content of this book and ed my level best 0
present the theory in very mpl and interesting way. ren though veiled my best te prowde
‘the most accurate matter the mistakesferrors might have gone untied yeu rdsome, the
please ring tt my notice would be highly appreciate,

el ha this book wl serve the moto mantaing the pace and pit of ou young mins
with which thas been we. Sillto serve the stant community ina beter way feedback nd
Suggestions of students and teacher ae invite,

Vikas Jain
CONTENTS

1

re

‘The Realm of Physics
Units and Measurements

Motion in Straight Line

1. Motion ina Plane

Newton's Laws of Motion
Friction

Work, Energy and Power

LUnear Momentum, Impulse and Collisions
Circular Rotational Motion

Gravitation

|The Wave Motion

Thermal Physics
Electrostaties

Current Electricity

Magnetism and Magnetic Effect of Current
Electromagnetic Induction (EM)

Optics

Basic Mathematics For Physics
‘Workout (1-6)

15
78
19-66
67-108
105-146
147-166
167.199
201-232
233-267
269-292
293-316
317335
337-368
369-415
417-440
441-458
459-502

503-543
545-560
Chapter

10

Gravitation

The First Steps’ Learning

* Newton’s Law of Universal Gravitation

© Earth's Gravity and Acceleration Due to Gravity
© Planetary Motion and Kepler's Laws

© Motion of Satellites in Circular Orbits

® Geosynchronous Satellites
270 | TheFiest Steps Physics

Throughout our dacusion of physics till now in this book, we always frequently
encountered the term ‘gravity force’ which is nothing but the measure of gravitational
fatiraction Beton the earth and an object on tts surface or near to its surfece. In present
‘hapter we shall explore this concept of gravitation in somewhat more deta

‘We have seen in chapter § (Newtons Laws of Maton that gravitational force is on of the
‘four basi forces that exist in the nature. La’ imagine that you make ajump to hick he bal,
‘and after Mcking, the bal doce’ come down and you are fling in lr. Ths incident seers to
‘bea fantasy, but this can be pooilef we were o have a gravity free world te, if there is no
“eravity, then you won't come back fo earth or nother words we can say, the gravitation
‘which binds us othe earth and ale holds the other planets and the sun in the solar system. In
‘broader sense isthe gravity which hale the universe ogether, and makes the ‘Newton's
Apples" fat the ground only. Iwas Sir esa Newton, who iret analyaed and interpreted the
‘eraitation in great dete! and propounded @ mathematical law related to gravitational
Phenomenon. Although many tcentists were able to understand the phenomenon of
{rauttatin before Newton, but none teas able fo formalate the things ina very precise terms.

Newton's Law of Universal Gravitation

1 has been said that once Sir Tntac 9 the earth's gravity force only, which 16
Newton was siting, in his” garden, and responsible to bind us withthe earth, holds the
thucrving the falling apple froma tree(which is atmosphere above the earth, falling of rain
{very common sight in apple growing regions drop tothe earth, motion of moon around the
for ordinary people, but intellectual brain of etvthand many mere illustrations canbe added
Newton sat anking vary of questions fom bei vue

‘Newton why the pple fing down ? Why it things were not yet over for Newton in
Neetu apc emus in a? aple iw pl raat, there was meting
fallmglows then why not the maon Or meen "OTE and even more revolutionary, was to be

Teas fuling dows ? applets faling down, 468d by Newton, and this comes in the forma

‘then some force must act on it according to my
second law ofmtion—whois exerting this force

of Newton's universal law of gravitation,
which states

“Every particle of the matter in the
universe attracts every other particle with
Newton to generalize the wea thatthe earth & force which is direetly proportional to
[tract allcbjects toward its centre. He also the product of their masses and inversely
{alized that same free ie, the force of proportional tothe square ofthe distance
{ravitaton governs the motion of fallin Detsreen them.
Lindalsothe motion ofmoon and thisrealization Consider two particles A and B of masses
(ot Newton was of gre ‘mp and my respectively, placed ata separa
‘This particular generalization of Newton, that ras ehown inthe fire, then from Newto
taribatrecta every object iowardsiscentto—a univer! law of eiaion tos ence sock
termed athe gravy ofearthor wecan say that ther with a force F whichis chevacteied by
it is the gravitational free experienced by
thjects due to earths gravity. The force with Feamymy, and
Srhich the earth attracts objects towards its pel
Contre termed a the earths gravity frc. Tt =
as
Fe to
Combining above two equations, we gt

‘universal constant of gravation, G dacs not
depend on place and time eval of Gat your
table and” lao at moon’ would be same
(e,independent of pcs, and the other truths
‘that the value of@ tan years back was same and
later ten years alto st would be the same. The
‘alae of @ is alo independent of the nature of
particles and the separation between them. As
alte of is doen’ depend upon any factor it
[eraid fo be universal constant «constant
‘whowe value remains constant and is
Independent of position and time. And forthe
fame reasons he Newto's aw of gravitation
flo ealled an universal law a8 is applicable
forall typen of particles having mass and is
valid at al lacs at all times.

io important to keep in mind that
[Newton's law of gravitation is valid ony for
point objects and not fr extended objects"
Titheugh Newton had’ done tedious
‘athematial calculations to show that if two
‘Spheres having uniform mass dsteibution”*
fre placed at a certain distance apart then the
‘Newon's law of gravitation gies the force of

rovtation | 271.

traction between them by considering ras
{he separation between thr eentres"
"Nos ze mention here ow ofthe important
points related to universal law of gravitation
(a) Te ea universal law, according to which
very, parle attracts overy other
particle ofthe universe, We shal discuss
‘out this in greater dtal towards the
nd ofthis ec
(0) The gravitational free betwoon two
particles And B acts along the line
JPining the particles IA experiences &
force Bard to B, then B experiences a
force Fas duct A uch that Bax =~ Fas,
fe both particles attract each other with

‘cua and opposite ree ven by "4

‘So we can say that gravitational free on
‘AandB due wo each other forms an
sction-reaction pa.

(o The gravitational force between two
particles is independent of the medium
present between them.

(@ Universal law af gravitation valid oven
for very small stances of the order of
10°" man well gor very lange distances

‘ofthe order of 10" m In other words, we
fan say that it Ie valid for atomic
‘istances a well tx for astronomical
‘itance,

(© Universal law of gravitation is valid for
tubatomie partie as well as fr
terrestrial ejecta ike planeta, tare ote

‘Tia aameTnes corpse wear ca wot cs
[irae lettin mrs maureen
272 | tees Step Physi

C-BIs
Concept Building Mlustrations

Mlustration | 1 Two parties of mass 10 Take mass ofthe earth, My = 10° ha,
‘eck re and a apart of 3 n,n rth y= 410" Rt
Determine the gravitational force between Solution Barth can bo connie oa wore
shen enfrm test, wo Know 4

Solution From universal lawet ravtation ifr aed ma spre cn tn
"ihe ‘ho ‘nnn ei
—— ‘phere Tine cust angen sown
Pn iota
Herem=mmat0K and rot
yeaa Moto .
“ aN A
stan." 8

“Just think that how much smal hire

Mlustration | 2. Teo spheres, one of mase
‘Ske and radius 10/om and eter of mase
0 bg and radive 20 om are placed at @

TPeahgo 68710" 610% 5

eho ame eraarten :
eeyicteee ete SR ae
Sai Ae doe “awe
eerie

“aad te

Mlustration | 4 The mass of the arth is
‘oc! kg and that of moon e410" hg
The distance between the centre ofthe moon
‘and earth 384° 10" hm Ascume both the
farth and moan to be uniform sphere
Determine the gravitational force
experienced bythe earth on moon.

Solution Using 7
parr?

oat

hare fy emus fearth alt 10g,

66710 5x10,

2 SF UN My Seman ofmon equal to 7.4% 10" ke
° Fy is separation between centre ef mn
*10 kn,
Mlustration | 3A Bock of mass HBO" 7.4510
‘laced onthe surface ofearth. Determine the aot
[ravtational force experienced by the block oe
Ciuetocarth 22010"
at ur tran ye net
on ipeeairarererrat
SM re nae
{ber mames andthe separation between tess
it ew con ya sans
Tn an hag leas week
‘ian’ ea ya
thatatin¢ Now omy a en
tr ened ae
‘rn yes Se
iieran ie rons)
fens otbang carte ange age
‘omit ovine e toh
Sproat ch Coe
‘Sane ers got
‘ample et useonier pou are sandngon the
etre) nd Tecan
‘Nearer erate ig
‘ota aay 1 Ey eo
‘Spon he grin pes mt
eat tecpttetasiegetin oe
siete Theol
vpn evant
Maem

867 10" 08 40
eS

=267 10° N

Earth’s Gravity and Accelerat

fou throw a all upwards then it comes
ck, motion of moon around the earth, mation
‘of sateltes around the earth, working of
Iiydowectrie power plants ete can be only made
pile because of earth's gravitation.

‘Barth atrct ll the Bodies which are in
‘the region of ts gravitational infuence, say a
‘uli dropped frm a igh tower, then it wll,
fall toward the surface of earth. if you drop a
‘ce of pape from sme eight, then it will also
{all towards tho surface of earth bt slowly a5
‘ampared to ball So, from thi observation can
Weer conclude thet under the earth's
os
wal

al slowly aa compared to heavier bodies?
No,becaut re aresstance also ating on
the abject a they are fling down,

Gravitation | 273

I we take coefficient of fiction between
your shoes and platform as j= 02, then the
Timiting friction fre between your shoes and
platform ef, = pong =0.2> 40% 9.8 = T8AN,

‘Now it means, minimum 78.4 N force
‘must act on you ta cause your motion, but the
iravitational force experienced by you due toa
‘ery bg oes (ran) negligible as compared
tominimm force required to cause your motion
fit cant cause your mation. But it doosn't
mean that gravitational fore can never cause
the mation in ustrations 8 and 4 you ean
arity sce that gravitational force is large
‘oagh to cause the mation ofbody. The concept
{stat it leat one ofthe bodes large ike
fun r earth or any other heavenly body) then
{ravitational force becomes comparable to the
{orc required fr mation and hence may cause
‘the motion. Prom illustration 4 you can infer
‘that moon Is experiencing a very large free
(=2 10” N) due to gravitational attraction of
‘arth, and it thi lange fre which males the
‘moon reve¥e arvund the earth, So, we ea
that moon is bounded to earth only de to
sravitatinal free of earth,

n Due to Gravity

Air Resistance

‘he force exerted by ae fretion termed
asairresstance. It valve depends on the mass
tf the abet, sts speed and its surface area,
‘Tehas been known earlier before Galileo)
that, when a feather and a stone are dropped
from same eight, then the stone wil reach the
ground fit and from” this people have
oneluded that lighter objets are fling lowly
ts compared to heavier objects inthe earths
iravty Galileo suggested that all objets a

gravity and e explained the observation onthe
Base that because of ae fiction the feather

falling slowly. Later on, Rabert Boyle also
experimentally explained the fact that bath the
274 | the Fst steps Phys

feather and the stone are falling with same
acceleration de to ear’ gravity He dropped
‘eather and ain from same height in a
Closed tll lata ited with a vacuum pun

(Geng ase to pump ou rand thas erating
‘eum tthe slash tube) and observed that
‘both the feather and the coin snk to the bottorn
‘oftube atthe same tie, thas showing tt bath
‘ve falling st anme rato under earth gravity
Tiother word, we cam say that acceleration af
al falling todies near the surface of earth is

provided air friction e melee.

"The ncleration of the body fling under
the car's gravitation lone is termed. as
acceleration det rat. Here, falling dcant
mean that the body is moving towards the
‘orth’ aurce, sca be moving up oie be

{projectile motion. Let us conser, a body of
‘mass m moving near the surface of earth under
‘the earths gravitational influence. twill
‘experience fore dueto earths grant ivenby

towards the centre arth

re he mao hy

siniat
item ofthe ty
‘ale crete

clear fom above expression tht aecleration of
‘body te independent of its mass.

‘This val of gis
arth ot forthe polnta near to the surface of
“arth whose height from the surface of arth
{eneplipible ax compared to te radius of eath
‘The aceleraion ofthe particle moving wader

carts gravity romaine the same (oth
Stngutade and direction), whether the partie
{Paling down, moving por moving some
{oye withthe horton, and in all aces, the
port i std trove feel under gravy.

‘The acecleratin due to gravity isnot
universal constant, ta value i afferent at
Uren potions, and it also depends on
Serio other factor.

‘Tatu conider a body fling freely under
carts gravity, ond shan Snatant Ht Isat 8
eight A om the eats surface a shown in
tho igure Here he nt negligible as compared
{othe radan ert, Rye
‘Te force exprianeed By the Body due to the
corte

Tr

‘nace,
ou,

we

So, acceleration due to gravity at a height
‘fom the surfce of earth ie

7 GM,
Rye nF
variation in acceleration due to gravity with
eight

I heey of =O, then gM

=9.8m which we have sendy seen

From above eprom we ean conde
tha os one moves ay fo te tra
tert he al of ¢dovanse Not oly Os
stot ecg vege ae
‘ine or ona gos fom cera repo
toler repo thea ob kp se tht

feclerton doo gravty dened separately