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MHT-CET : Physics Entrance Exam

MHT - CET : Physics - Electomagnetic Induction Know More

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        I.            Self Inductance of a Coil:

The self inductance (L) is given by L = 



Where m0 =

permeability of free space

N =

total number of turns

A =

area of cross-section of coil

l =

length of the coil.


    IV.            Mutual Inductance Between Two Coils:

The mutual inductance (M) is given by M = m0 



      V.            Where N, N2 = number of turns of the two coils.

    VI.            Wattless Current:
If an alternating circuit contains a pure inductor or a pure capacitor only, its ohmic resistance is zero. The phase difference between the current and the voltage in such a circuit is 90. Thus, the power in the circuit P = Erms Irms cos
f = Erms Irms cos 90 = 0.
Hence, there is no dissipation of energy in the circuit. The current in such a circuit is called wattless current.

VII.            Time Constant:
(a) L
-R Circuit:

                                             When key K is pressed the current in the circuit (shown above) starts from 0 and increases to a maximum value I0. The growth of current is given by the equation I = I0 (1 - e (R/L)t)
Where I0 = steady value of current at
t = .
The following graph shows the variation of I with


                                             The rate of increase of current becomes less as I approaches I0, it is proportional to R/L.

                                             The ratio is called the time constant and is denoted by l. The time constant l of a circuit is the time taken by the current to rise from zero to 0.632 or 63.2% of its final value.

b) C - R circuit:


                                             If key K is closed, the charge on the capacitor increases according to the equation q = CE (1 - e- -t/RC) = q0 (1 - e- -t/RC).

                                             The product RC is called the time constant (l) of the circuit. It is the time taken by the capacitor to aquire 0.632 or 63.2% of its maximum charge.

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