Explanation
The correct answer is option (B).
Hint: Calculate the magnetic flux and use it to find out the mutual inductance.
Step 1: Calculate magnetic flux of smaller loop.
Let the length of the larger square and the smaller square be L and l respectively. Accordingly, the current in these two square loops are I and i.
According to Faraday’s first law of electromagnetic radiation, whenever magnetic flux passes through surface changes with respect to time, an induced EMF is generated. Magnetic field at a distance L2 from the centre of the current carrying wire of length L is given by:
B1=μ04πiL22sin45
B1=μ04πi×2×2sin×1√2L
Magnetic field in the centre of square due to four wires of length L will be:
B1=μ04π4×i×2×2sin×1√2L
B1=μ0π2√2iL
Since, the smaller loop is at the centre of the larger loop, so L>>l
In a small square, the magnetic field is uniform and is equal to B1
Flux in the smaller loop will be:
ϕ=B1l2
ϕ=μ0π2√2il2L
Step 2: Calculate the mutual inductance.
Mutual inductance is given by –
M=ϕi
M=μ0π2√2l2L
M∝l2L
Hence, the mutual inductance of the system is proportional to l2L.
Given,
Angular frequency ω=2πf=2π180060=60π
Magnetic field, B=0.5 G=0.5×10−4 T
Area, A=π×0.072=0.0154m2
Flux ϕ=nBAcosθ=nB(πr2)cosωt
The induced emf is
ε=−dϕdt=nBAωsinωt
For maximum E.M.F, ε=εo, sinωt=1
εo=nωBA
εo=4000×60π×0.5×10−4×0.0154
εo=0.58V
Velocity, V=10cm/s
Length of rod, L=50cm
Magnetic Field, B=10G
Motional emf=BlVsinθ=10×50×10sin30o=2500 CGS unit
A conducting disc of radius R is rotating with angular velocity ω.Mass of electron is and charged e. If electrons are the current carries in a conductor, the potential difference between the center and the edge of the disc is:
Given that,
Self-inductance of coil = 2.0H
Let the current flowing through the coil be 2A at time t2
Now,
2=2sint2
t=√π2
Now, the amount of energy spent during the period when the current changes from 0 to 2 A
Now, Self-induced e. m. f
E=Ldidt
Now, the work done is
dW=L(didt)dq
dW=L×didt×idt
dW=Lidi
Now, on integrate
∫dW=t∫0Lidi
W=t∫0L2sint2d(2sint2)
W=t∫08Lsint2cost2tdt
W=4Lt∫0sin2t2dt
Now, let
θ=2t2
dθ=4tdt
dt=dθ4t
Now, put the value of 2t2and dt
W=4Lt∫0sinθdθ4
W=L[(−cosθ)]t0
W=−L[cos2t2]t0
W=−L[cos2t2]√π20
W=2L
W=2×2
W=4J
Hence, the amount of energy is 4 J
The disc is rotating in magnetic field from North to South.
If the direction of the magnetic field is perpendicular to the plane of the disc:
Viewing disk from the top.
Force on each proton is toward the inside, and force on each electron is outside.
So, the negative charge will develop, in the outskirt of the disk, and the positive charge will develop at the center.
Hence, Current will flow from P to Q.
Alternatively:
If the magnetic field is perpendicular to the normal vector of the plane of the disc:
The emf induced will not be radial, as governed by flaming's right hand rule, thus no current will flow through the resistance R.
The rate of change of magnetic flus is called as induced emf. To induce an emf, magnetic field must be changing. When the flux in the graph is constant then there is no magnetic field and hence no emf induces.
Induced emf is negative times the rate of change of flux.
So, induce emf is shown in graph 3
When both coil and magnet moves in same direction, then there will be no induced emf in the coil because there is no change in the magnetic flux. If both are moves in same direction, then induced emf in coil is zero. The induced emf is given by:
emf=−dϕdt=−d(BA)dt
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