A uniform but time varying magnetic field is present in a circular region of radius ' $R$ '. The magnetic field is perpendicular and into the plane of loop and the magnitude of field is increasing at a constant rate $\alpha$. There is a straight conducting rod of length 2 R placed as shown in figure. The magnitude of induced emf across the rod is

$\pi \mathrm{R}^2 \alpha$
$\frac{1}{2} \pi \mathrm{R}^2 \alpha$
$\frac{1}{\sqrt{2}} \mathrm{R}^2 \alpha$
$\frac{1}{4} \pi \mathrm{R}^2 \alpha$
From a tower of height $H$ ,a particle is thrown vertically upwards with a speed $u$ .The time taken by the particle to hit the ground is $n$ times that taken by it to reach the highest point of its path.The relation between $H, u$ and $n$ is
$2 g H=n^2 u^2$
$g H=(n-2)^2 u^2$
$2 g H=n u^2(n-2)$
$2 g H=u^2(n-2)^2$
There is a ring of radius $r$ having linear charge density $\lambda$ and rotating with a uniform angular velocity $\omega$. The magnitude of the magnetic field produced by this ring at its own centre would be ( $\mu_0=$ permeability of air)
$\frac{\lambda \omega^2}{2-\mu_0}$
$\frac{\mu_0 \lambda^2 \omega}{\sqrt{2}}$
$\frac{\mu_0 \lambda \omega}{2}$
$\frac{\mu_0 \lambda}{2 \omega^2}$
Three vectors $\vec{a}, \vec{b}$ and $\vec{c}$ are such that $|\vec{a}|=1,|\vec{b}|=2$ and $|\vec{c}|=4$ along with $\vec{a}+\vec{b}+\vec{c}=0$ .Then,the value of $4 \vec{a} \cdot \vec{b}+3 \vec{b} \cdot \vec{c}+3 \vec{c} \cdot \vec{a}$ will be
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-68 problem is wrong.
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