Electromagnetic Induction And Alternating Current Class 12 Pdf Download

Chapter 4 ELECTROMAGNETIC INDUCTION AND ALTERNATING CURRENTS

• The phenomenon of production of induced emf in a conductor when electric flux linked with that changes is called electromagnetic induction.

• Magnetic flux through a surface of area A placed in a uniform magnetic field B is defined as Cosθ where θ is the angle between B and A.

• Magnetic flux is a scalar quantity and its SI unit is weber (Wb).

First Law: When magnetic flux linked with the conductor changes, induced emf produces across it. Second Law:

The magnitude of the induced e.m.f in a circuit is equal to the rate of change of magnitude flux linked with that circuit

The direction of induced current or the polarity of the induced e.m.f is in such a way that it opposes the cause that produces it. (The negative sign in Faraday’s law indicates this fact.) Lenz law obeys the principle of energy conservation.

• The induced current in a closed loop can be produced by changing the

(i) magnitude of B

(ii) area A of the loop

(iii) its orientation in magnetic field.

• The direction of induced current is obtained from Fleming’s right hand rule.

• When a metal rod of length l is placed normal to a uniform magnetic field B and moved with a velocity v perpendicular to the field, the induced e.m.f is called motional e.m.f. It produces across the ends of the rod. ε = Blv.If ‘R’ is the resistance of the metal rod, the induced current is given by I=Blv/R, the force acting on the conductor in the presence of magnetic field (due to drift of charge) is given by F =B^{2}l^{2}v / R. The power required to move the conductor with a constant speed is given by P= B^{2}l^{2}v^{2}/R.

• The induced currents produced on the surface of a thick conductor when magnetic flux linked with that changes are called eddy currents.

• The phenomenon of production of induced emf in a coil itself when electric current passing through that changes is called self induction. Self Inductance is the ratio of the flux linkage to current. =

• When a current in a coil changes it induces a back e.m.f in the same coil. The self induced e.m.f is given by ε = where L is the self-inductance of the coil. It is a measure of inertia of the coil against the change of current through it. Its S.I unit is henry (H).

• The inductance is said to be one Henry when an emf of one volt induces in a coil for unit rate of change of electric current through it.

• The changing current in a coil can induce an e.m.f in a nearby coil. This
relation, ε = shows that Mutual inductance of coil 1 with respect to coil
2 (M_{12}) is due to change of current in coil 2. (M_{12} =M_{21}).

• The self-inductance of a long solenoid is given by L = μ_{0}n^{2}Al where A is the
area of cross-section of the solenoid, l is its length and n is the number of turns
per unit length.

• The mutual inductance of two co-axial coils is given by M_{12} = M_{21} = μM^{0}
n_{1}n_{2}A_{l} where n1& n2 are the number of turns per unit length of coils 1 & 2. A is the
area of cross-section and l is the length of the solenoids.

• Energy stored in an inductor in the form of magnetic field is and Magnetic energy density

• The electric current whose magnitude changes continuously and direction
changes periodically is called alternating current (AC). I = Io Sin ωt.
• The root mean square value of a.c. may be defined as that value of steady
current which would generate the same amount of heat in a given resistance in a
given time as is done by the a.c. when passed through the same resistance during
the same time. Irms = I_{o}/√2 = 0.707i0 . Similarly, vrms = v_{o}/√2 = 0.707v_{o}.

• The rotating vectors which represent the varying quantities are called phasors. The diagram in which the AC voltage and AC currents are represented as phasors is called phasor diagram.

• The opposition offered by resistor is called resistance (R). The non-resistive opposition offered by a device is called reactance (X). The combination of reactance and resistance is called impedance (Z).

• An alternating voltage ε=ε_{0}Sinωt, applied to a resistor R drives a current I =
I_{0}Sinωt in the resistor, I_{0} = ε_{0} /R where ε_{0}& I_{0} are the peak values of voltage and
current. (also represented by V_{m} & I_{m})

• For an AC e_{m}f ε = ε_{m} Sin ωt applied to a resistor, current and voltage are in
phase.

• In case of an a.c. circuit having pure inductance current lags behind e.m.f by
a phase angle 90°. ε = εm Sin ωt and i = i_{m} Sin (ωt-π/2). I_{m} = ε_{m}/X_{L}; X_{L} = ωL is
called inductive reactance.

• In case of an a.c. circuit having pure capacitance, current leads e._{m}.f by a
phase angle of 90°. ε = ε_{m}Sinωt and I= I_{m}Sin(ωt+π/2) where I_{m} = ε_{m}/X_{C} and X_{C} =
1/ωC is called capacitive reactance.

• In case of an a.c. circuit having R, L and C, the total or effective resistance of the circuit is called impedance (Z).

• Average power loss over a complete cycle in an LCR circuit is P =
ε_{rms}I_{rms}CosΦ

• In a purely resistive circuit Φ = 0; P = V_{RMS}I_{RMS}.

• In a purely inductive circuit Φ = π/2; P = 0.

• In a purely capacitive circuit Φ = π/2; P = 0.

• The electric current in an AC circuit is said to be wattless current when average power dissipated or consumed is zero.

• In an LCR circuit, the circuit admits maximum current if X_{C} = X_{L}, so that Z
= R and resonant frequency w_{r}

• The device which converts mechanical energy in to AC electrical energy by virtue of electromagnetic induction is called AC Generator.

• Rotation of rectangular coil in a magnetic field causes change in flux (Φ =
NBACosωt). Change in flux induces e.m.f in the coil which is given by ε= -dΦ/dt = NBAωSinωt. ε = ε_{0}Sinωt. Current induced in the coil I = ε/R = ε_{0}Sinωt/R =
I_{0}Sinωt

• The device which converts an AC voltage of one value to another is called Transformer. For an ideal transformer,• In an ideal transformer, εPIP = εSIS. i.e

• If N_{S}>N_{P}; ε_{S>}ε_{P}& I_{S}< I_{P} – step up. If N_{P}>N_{S}; εP>ε_{S} & I_{P}I_{S} – step down.

• Losses in transformer: Copper losses; Iron losses, Flux losses; Hysteresis losses; Humming losses.

• When a charged capacitor is allowed to discharge through an inductor, electrical oscillations of constant amplitude and frequency are produced, which is called LC oscillations. The charge on capacitor q satisfies the equation of SHM

•

Please send your queries to ncerthelp@gmail.com you can aslo visit our facebook page to get quick help. Link of our facebook page is given in sidebar

- Chapter 5: Magnetrism And Matter
- chapter 1 ELECTROSTATICS
- Chapter 2 CURRENT ELECTRICITY
- Chapter 3 Agnetic Effects Of Current And Magnetisml
- Chapter 4 ELECTROMAGNETIC INDUCTION AND ALTERNATING CURRENTS
- Chapter 5 Electro Magnetic Waves
- Chapter 6 Optics Ray Optics
- Chapter 7 Dual Nature Of Matter & Radiation
- Chapter 8 Atoms & Nuclei
- Chapter 10: Wave Optics
- Chapter 14: Semiconductor Electronics, Materials, Devices and Sample Circuits

- NCERT Solutions for Class 9 Science Maths Hindi English Math
- NCERT Solutions for Class 10 Maths Science English Hindi SST
- Class 11 Maths Ncert Solutions Biology Chemistry English Physics
- Class 12 Maths Ncert Solutions Chemistry Biology Physics pdf

- Class 1 Model Test Papers Download in pdf
- Class 5 Model Test Papers Download in pdf
- Class 6 Model Test Papers Download in pdf
- Class 7 Model Test Papers Download in pdf
- Class 8 Model Test Papers Download in pdf
- Class 9 Model Test Papers Download in pdf
- Class 10 Model Test Papers Download in pdf
- Class 11 Model Test Papers Download in pdf
- Class 12 Model Test Papers Download in pdf

Copyright @ ncerthelp.com A free educational website for CBSE, ICSE and UP board.