Engineering Competition Physics Questions

Blazing goIITian

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24 Oct 2009 15:37:42 IST
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24 Oct 2009 15:37:42 IST
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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 = r0n2LA
 
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 cross-sectional area of the solenoid.
 
 
Mutual Inductance:
 
A changing current in one circuit causes a changing Flux &
hence an induced Emf in a neighbouring circuit.
 
N22 = Mi1
 
Where M is the Mutual Inductance of coils 1  2
 
M = N22/i1 = N11/i2
 
1 = -M di1/dt
 
2 = -M di2/dt
 
Alternating Current and Voltage:
 
Current and Voltage varying Sinusoidally are called as AC
and AV (Alternating Current and Voltage)
 
V = V0Sint
 
i = i0Sint
 
 
Mean Values of Voltage and Current:
 
(a)In one complete cycle:
 
V = 0 , i = 0
 
(b)In Half Cycle:
 
V = 2V0/ , i = 2i0/
 
(c)Root mean square Values:
 
Vrms = V0/2
 
irms = i0/2
 
Where V0 and i0 are peak Voltage and current.
 
 
AC Circuit with a Resistor:
 
E = E0Sint = E0Sint/R
 

AC Circuit with a capacitor:
 
V = E0Sint
 
i = E0/(1/C) [ Sin(t+/2) ]
 
Xc = 1/C is capacitive Reactance.
 
i = i0Sin(t + /2)
 
 
AC Circuit with an inductor:
 
V = E0Sint
 
i = i0Sin(t - /2)  {Voltage Leading}
 
XL = L Inductive Reactance.
 
 
LCR Circuit (Inductor,capacitor,Resistor Circuit in series):
 
Impedance , Z =  (L - 1/C)2 + R2
 
The above Expressino can be very well be given as:
 
Z = (XL-XC)2 + R2 ,
 
For Phase angle
 
Tan = XL-XC/R
 
 
Resonance:
 
 
L = 1/C
 
The Impedance of the circuit is equal to R only.
 
0 = 1/LC
 
f0 = 1/2LC  (Resonance Frequency)
 
 
Power:
 
Average Power ,
 
Pavg = Erms.Irms.Cos 
 
Pavg = 1/2*E0I0Cos
 
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 + R2
 
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)


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..............

Blazing goIITian

Joined: 11 Sep 2008 12:38:20 IST
Posts: 1159
13 Nov 2009 20:22:19 IST
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good contribution

Blazing goIITian

Joined: 25 Jul 2009 21:09:59 IST
Posts: 615
13 Nov 2009 20:23:14 IST
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thanks more comments are invited

Blazing goIITian

Joined: 8 Oct 2008 14:46:21 IST
Posts: 8064
13 Nov 2009 22:42:08 IST
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excellent dude

Hot goIITian

Joined: 1 Sep 2009 20:37:43 IST
Posts: 172
13 Nov 2009 22:43:44 IST
0 people liked this

thanx a lot......... xcellent job........

Cool goIITian

Joined: 26 Jun 2009 21:41:21 IST
Posts: 90
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>>

Blazing goIITian

Joined: 25 Jul 2009 21:09:59 IST
Posts: 615
15 Nov 2009 09:30:16 IST
0 people liked this

thanks more comments are invited

Blazing goIITian

Joined: 9 May 2009 09:33:23 IST
Posts: 831
15 Nov 2009 10:13:12 IST
0 people liked this

yeah gud job dude ...5 more....

Hot goIITian

Joined: 2 Apr 2009 14:09:47 IST
Posts: 161
15 Nov 2009 21:08:54 IST
0 people liked this

nice one yaar.........

Blazing goIITian

Joined: 25 Jul 2009 21:09:59 IST
Posts: 615
16 Nov 2009 20:05:34 IST
0 people liked this

thanks more comments are invited

Blazing goIITian

Joined: 9 May 2009 21:08:29 IST
Posts: 766
17 Nov 2009 19:09:57 IST
0 people liked this

really a very good post dude!

New kid on the Block

Joined: 25 Jul 2008 19:51:41 IST
Posts: 2
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!!!!

New kid on the Block

Joined: 25 Jul 2008 19:51:41 IST
Posts: 2
18 Nov 2009 18:06:48 IST
0 people liked this

sorry that was electromagnetism

Blazing goIITian

Joined: 25 Jul 2009 21:09:59 IST
Posts: 615
19 Nov 2009 19:01:14 IST
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thanks dude >>>>>>>>>>>>> but still i expect more comments !!

Cool goIITian

Joined: 22 Nov 2008 15:50:27 IST
Posts: 45
23 Nov 2009 18:19:56 IST
0 people liked this

gud job yaar...keep up the gud work

New kid on the Block

Joined: 24 Mar 2009 17:20:02 IST
Posts: 3
23 Nov 2009 20:01:00 IST
0 people liked this

THANKS A LOT YAAR VERY USEFUL..

New kid on the Block

Joined: 11 Sep 2011 16:51:10 IST
Posts: 1
11 Sep 2011 16:51:13 IST
0 people liked this

u did a fabulous job dude. thankx..............

Scorching goIITian

Joined: 1 Jun 2011 05:26:27 IST
Posts: 207
11 Sep 2011 17:30:45 IST
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Nice post dude ..Thankzz a lot brthr ;-)



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