Welcome toPHYSICS –I (PH10001)
Sir Isaac Newton Thomas Young
Albert Einstein
Niels Bohr Werner Heisenberg
Christiaan Huygens
Course Content
Oscillations – 8 lectures Waves - 8 lectures Interference - 7 lectures Diffraction - 7 lectures Polarisation - 4 lectures Quantum Physics - 8 lectures
L-T-P 3-1-0
Instructor: Dr. Anushree Roy
Contact number : 83856
Availability :Venue: Room No. C133 in main buildingTime : Thursday 5.00-6.30 pm
Slides other details available at: www.webteam.iitkgp.ernet.in/physics1
Class Timings
Monday: From 1.30 to 2.30(door will close at 1.40) Tuesday: From 3.30 to 5.30(door will close at 3.45)
Mid semester exam: 30
End semester exam: 50
Tutorial: 20
Marks Break-up
www.webteam.iitkgp.ernet.in/physics1
BOOKS
FEYNMAN LECTURES ON PHYSICS VOL I
THE PHYSICS OF VIBRATIONS AND WAVESby H. J. PAIN
FUNDAMENTALS OF OPTICSby JENKINS AND WHITE
OPTICSby EUGENE HECHT
1. LECTURE NOTES & PROBLEMS BANK forPHYSICS by SARASWAT AND SASTRY
3. LECTURE NOTE S AND PROBLEMS BANKby SAYAN KAR at
http://www.cts.iitkgp.ernet.in/Phy_1st/tut.html
Audio lecture: www.webteam.iitkgp.ernet.in/physics1
2. PHYSICS I: OSCILLATIONS AND WAVES by BHARADWAJ AND KHASTAGIR
Discussion Forum
https://www.facebook.com/groups/523462897801020/
OSCILLATION
HARMONIC OSCILLATION
OSCILLATION
SPRING SIMPLE HARMONIC MOTION
Equation of motion
2
2
d xm kx
dt
mm
mm
xmax
max
Assumption : spring is perfectly linear
force of pulling back restoring force -x
xHOOKE’S LAW
k : stiffness constant
second order: because the highest derivative is second order.
ordinary: because the derivatives are only with respect to one variable (t).
homogeneous: because x or its derivatives appear in every term, and
linear: because x and its derivatives appear separately and linearly in each term
Second order ordinary homogenous linear differential eqn.
One of the solutions of the differential equation
0cosx A t
0
k
m
A is a constant : Amplitude of motion
wo refers to natural motion the spring
Velocity :
Acceleration :
tadt
dx sinv
tadt
xd cosa 22
2
Oscillation!
For A=1
0.0 0.1 0.2
-1.0
-0.5
0.0
0.5
1.0
0t
x
Time pattern of the motion is independent A
A is amplitude of motion
Physical significance of A
0 0cos cos ( 2 )t t
Motion repeats when changes by 2p
: Phase of the motion
t0
t0
Physical significance of w0
0 2T
T: Time period of motion
0
22
mT
k
Phase estimation
0
2
T
0 1 2 3-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
0 1 2 3-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
t
x
20 For black curve
For red curve 40
Shifting the beginning (origin) of the time
General solution
t1 = some constant
0 1cos ( )A t t Form
1010
00
10
0
10
sin coswith
sincos
where
)cos(
)(cos
tAEtAD
tEtDx
t
tAx
ttAx
w0: angular freq. (amount of phase change in 1 sec)
(w0t+f) : phase of the oscillation
f: phase shift from some defined origin of time
0 0
0 0 0 0
cos sin
v sin cos
x D t E t
D t E t
Initial conditions to determine D and E
At t =0 x=x0 and v=v0
0
0 0 0 0
0
0
0
.1 .0
v .0 .1
v
x D E D
D E E
D x
E
Estimating Amplitude and Phase from Initial conditions
Hence find amplitude and phase
Velocity :
Acceleration :
0 0v sin( )dx
A tdt
22 2
0 0 02cos( )
d xa A t x
dt
0cos( )x A t
Potential energy of the spring-mass system
Potential energy :2 2 2
0
20
1 1cos ( )
2 21
[1 cos 2( )]4
kx kA t
kA t
Kinetic energy of the spring-mass system
Kinetic energy :2 2 2 2
0 0
2 20 0
1 1v sin ( )
2 21
[1 cos 2( )]4
m m A t
m A t
Total energy = K.E + P.E 2 20
1
2m A
Total energy of the spring-mass system
Assumption : massless unstretchable string
Simple Pendulum
sin
4 sin
ml mg
0
2
g
l
lT
g
0
m
q
l
g
Harmonic and circular motion (only an Analogy)
Acceleration (a) R20
cos
sin
x R
y R
Geometrically
cosxa a 2 20 0cosR x
x component of the displacement of a particle moving along a circular path with uniform speed is a SHM
qR
X
yv
•Every oscillatory motion or periodic motion has a frequency=2w pf
Unit of f : 1Hertz = 1Hz = 1 oscillation/sec =1sec-1
•The period T is the time required for one complete oscillation or cycle
1T
f
•Displacement during SHM as a function of time
maxx cos( )x t xmax: amplitude
•Velocity during SHM as a function of time
•Acceleration during SHM as a function of time
maxv sin( )x t
wxmax: velocity amplitude
2max cos( )a x t
w2xmax: acceleration amplitude
xmax=A
FEYNMAN LECTURES ON PHYSICS VOL I
Author : RICHARD P FEYNMAN,
IIT KGP Central Library :
Class no. 530.4