Engineering Competition Physics Questions
24 Oct 2009 15:37:42 IST
Engineering Competition Physics Questions
Engineering Entrance
,
JEE Main
,
JEE Main & Advanced
,
Physics
,
Electromagnetism
,
academic
electromagnetic Induction:
The Production of Electromotive force in a conductor when
there is a change in the magnetic flux linkage with coil or
when there is a relative motion of the conductor across a
magnetic field.
Magnetic Flux:
Magnetic Flux through an area dS in a magnetic Field B is
= B.dS
Faraday's Law:
When the Flux of a magnetic field through a loop changes,
an emf is induced in the loop which is given by :
= d/dt
Where
= B.dS is the Flux through the loop.
The EmF lasts as long as the magnetic Field changes.
Lenz's Law:
It states that the polarity of the induced Emf and the
direction of the induced current is such tat it opposes the
change that has induced it.
Motional Emf:
When a conducting rod of length L moves with a velocity V
in a magnetic field B such that B,V & L are mutually per
pendicular to each other then the induced Emf is :
= BLV
This is called as motional Emf.If the circuit is completed
the direction of the current can be worked out by Lenz's
Law.
Induced Electric Field:
A time varying Magnetic field induces an electric field.If
a conductor is placed in this field , an induced Emf is
produced :
= E.dL (Here is Cyclic Integral)
=  d/dt
E.dL =  d/dt (Cyclic Integral)
Self Induction:
A Current Carying loop produces a magentic Flux Through
the area.
= Li Where L is the Self Inductance.
If Current Changes in the loop the Induced Emf is given
by:
=  d/dt = L di/dt
For a Solenoid of n turns,
= n d/dt B.dS
Self Inductance of a long solenoid is:
L = _{r}_{0}n^{2}LA
Where
_{r} is the relative magnetic permeability of the core , n is
no. of turns per unit length , L is the length of solenoid.
and A is the crosssectional area of the solenoid.
Mutual Inductance:
A changing current in one circuit causes a changing Flux &
hence an induced Emf in a neighbouring circuit.
N_{2}_{2 }= Mi_{1}
Where M is the Mutual Inductance of coils 1 2
M = N_{2}_{2}/i_{1} = N_{1}_{1}/i_{2}
_{1} = M di_{1}/dt
_{2 }= M di_{2}/dt
Alternating Current and Voltage:
Current and Voltage varying Sinusoidally are called as AC
and AV (Alternating Current and Voltage)
V = V_{0}Sint
i = i_{0}Sint
Mean Values of Voltage and Current:
(a)In one complete cycle:
V = 0 , i = 0
(b)In Half Cycle:
V = 2V_{0}/ , i = 2i_{0}/
AC Circuit with a capacitor:
(c)Root mean square Values:
V_{rms }= V_{0}/2
i_{rms} = i_{0}/2
Where V_{0 }and i_{0} are peak Voltage and current.
AC Circuit with a Resistor:
E = E_{0}Sint = E_{0}Sint/R
AC Circuit with a capacitor:
V = E_{0}Sint
i = E_{0}/(1/C) [ Sin(t+/2) ]
X_{c} = 1/C is capacitive Reactance.
i = i_{0}Sin(t + /2)
AC Circuit with an inductor:
V = E_{0}Sint
i = i_{0}Sin(t  /2) {Voltage Leading}
X_{L} = L Inductive Reactance.
LCR Circuit (Inductor,capacitor,Resistor Circuit in series):
Impedance , Z = (L  1/C)^{2} + R^{2}
The above Expressino can be very well be given as:
Z = (X_{L}X_{C})^{2} + R^{2} ,
For Phase angle
Tan = X_{L}X_{C}/R
Resonance:
L = 1/C
The Impedance of the circuit is equal to R only.
_{0} = 1/LC
f_{0} = 1/2LC (Resonance Frequency)
Power:
Average Power ,
P_{avg} = E_{rms}.I_{rms}.Cos
P_{avg} = 1/2*E_{0}I_{0}Cos
Where Cos is the power factor.
Cos = R/Z
Choke Coil:
A Coil with low resistance and high inductance used to reduce current in AC Circuit without much heat loss is
called as a Choke Coil.
Power factor , Cos = R / (L  1/C)^{2} + R^{2}
R is Low and L is High thus is Reducing current.
Hope you all find it useful.
I have typed this whole thing
plZ rate me if useful.
Cheers!!!!!!!!!!!!@@@@@@!!!!!!!!!!!
Comments (18)
Vijay Pal
Forum Expert
Joined: 1 Jun 2009 13:31:11 IST
Posts: 2456
13 Nov 2009 13:11:38 IST
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nice post..............
14 Nov 2009 22:14:43 IST
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THNXX ALOT 4 SUCH GREAT COLLECTION OF BRIEF NOTES>>>INVALUABLE MAN>>>THUMBX UP 4 AHEAD>>
18 Nov 2009 18:06:21 IST
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thanks a lot for the post........Its like the whole of magnetism covered in here!!!!
19 Nov 2009 19:01:14 IST
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thanks dude >>>>>>>>>>>>> but still i expect more comments !!
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