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301.

A parallel plate capacitor of plate separation `2 mm` is connected in an electric circuit having source voltage `400 V`. If the plate area is `60 cm^(2)`, then the value of displacement current for `10^(-6) sec` will beA. `1.062 amp`B. `1.062xx10^(-2)amp`C. `1.062xx10^(-3)amp`D. `1.062xx10^(-4)amp`

Answer» Correct Answer - b
`I_(D)=epsilon_(0)(dphi_(E))/(dt)=epsilon_(0)(EA)/(t)=epsilon_(0)((V)/(d)).(A)/(t)`
`=(8.85xx10^(-12)xx400xx60xx10^(-4))/(10^(-3)xx10^(-6))=1.602xx10^(-2)amp`
Discussion
302.

If `epsi_(0)` and `mu_(0)` are respectively, the electric permittivity and the magnetic permeability of free space, `epsi` and `mu` the corresponding quantities in a medium, the refractive index of the medium isA. `sqrt((muepsi)/(mu_(0)epsi_(0)))`B. `(muepsi)/(mu_(0)epsi_(0))`C. `sqrt((mu_(0)epsi_(0))/(muepsi))`D. `sqrt((mumu_(0))/(epsiepsi_(0)))`

Answer» Correct Answer - A
Refractive index, `eta = (c)/(v) ((1)/(sqrt(mu_(0)epsi_(0))))/((1)/(sqrt(muepsi)))=sqrt((muepsi)/(mu_(0)epsi_(0)))`
Discussion
303.

A plane e.m. wave travelling along the x-direction has a wavelength of 3mm. The variation in the electric field occurs in the y-direction with an amplitude `66Vm^-1`. The equation for the electric and magnetic fields as a function of x and t are respectivelyA. `E_y=33cos pixx10^(11)(t-x/c)` `B_z=1.1 xx10^-7cos pixx10^(11) (t-x/c)`B. `E_y=11cos 2pixx10^(11)(t-x/c)` `B_y=11 xx10^-7cos 2pixx10^(11) (t-x/c)`C. `E_x=33cos pixx10^(11)(t-x/c)` `B_y=11 xx10^-7cos pixx10^(11) (t-x/c)`D. `E_y=66cos pixx10^(11)(t-x/c)` `B_z=2.2 xx10^-7cos 2pixx10^(11) (t-x/c)`

Answer» Correct Answer - d
`lambda=3mm=3xx10^-3m , E_0=66Vm^-1`
`B_0=(E_0)/c =66/(3xx10^8)=2.2 xx10^-7T`
As em wave is propagating along
x-axis and electric field variation is along
y-direction, the magnetic field variation is along
z-direction.
Using the relation for harmonic wave
`E_y=E_0cos .(2pi)/lambda(ct-x)`
`E_y=E_0cos .(2pic)/lambda(t-x/c)`
`:. E_y=66cos .(2pixx3xx10^8)/(3xx10^-3)(t-x/c)`
`=66 cos 2pixx10^(11)(t-x/c)`
and `B_z= B_0cos .(2pic)/lambda(t-x/c)`
`=2.2xx10^-7cos 2pixx10^(11)(t-x/c)`
Thus, option (d) is correct.
Discussion
304.

The waves used in telecommunication areA. `IR`B. `UV`C. MicrowavesD. Cosmic rays

Answer» Correct Answer - c
In telecommunication, microwaves are used.
Discussion