A circular coil of radius $r=10 c m$ having 300 turns carries a current of 2 A . The coil is suspended vertically in a uniform magnetic field of strength 0.7 T . If the plane of the coil makes an angle $30^{\circ}$ with the magnetic field, the torque needed to prevent it from turning is:
11.42 Nm
1.1 Nm
22.84 Nm
5.71 Nm
The width of the fringes obtained with a light of wave length $6.2 \times 10^{-8} \mathrm{~m}$ is 1.82 mm . If the whole apparatus is immersed in a liquid of refractive index 1.3 , what will be the width of the resulting fringe?
1.4 mm
0.71 mm
2.8 mm
1.82 mm
If $\mu_0$ is the permeability of free space and $\varepsilon_0$ permittivity of free space then the dimension for $\left(\mu_0 \varepsilon_0\right)^{1 / 2}$ is :
$\left[M L^{-1} T\right]$
$\left[M L T^{-1}\right]$
$\left[L^{-1} T\right]$
$\left[L^{-1} T^{-1}\right]$
An electric field and magnetic field $1.8 \times 10^4 \mathrm{Vm}^{-1}$ and $6 \times 10^{-3} \mathrm{~T}$ respectively are applied simultaneously on an electron beam such that path of the beam remains undeviated, then the speed of the electron will be:
$1.5 \times 10^6 \mathrm{~ms}^{-1}$
$3 \times 10^7 \mathrm{~ms}^{-1}$
$3 \times 10^6 \mathrm{~ms}^{-1}$
$1.5 \times 10^7 \mathrm{~ms}^{-1}$
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