Rutherford's experiment on scattering of $\alpha-$particles showed for the first time that the atom has

The transformed equation of $3x^2 + 3y^2 + 2xy = 2$,when the coordinate axes are rotated through an angle of $45^{\circ}$,is

If $L: ax + by + c = 0$ is a variable straight line,where $a, b$ and $c$ are the second,fourth and seventh terms of an $AP$ respectively,then $L$ passes through the fixed point -

Electric field at a point varies as $r^0$ for

$A$ common emitter transistor amplifier has a current gain of $50$. If the load resistance is $4 \ k\Omega$ and input resistance is $500 \ \Omega$,the voltage gain of the amplifier is

The cork cambium, cork, and secondary cortex are collectively called $........$.