If the circle $x^2+y^2+6x-2y+k=0$ bisects the circumference of the circle $x^2+y^2+2x-6y-15=0$,then $k=$

If the peak value of the magnetic field of an electromagnetic wave is $30 \times 10^{-9} \ T$,then the peak value of the electric field is (in $Vm^{-1}$)

If $X$ is a Poisson variate such that $\alpha = P(X=1) = P(X=2)$,then $P(X=4)$ is equal to

$A$ ray of light of intensity $I$ is incident on a parallel glass-slab at a point $A$ as shown in the figure. It undergoes partial reflection and refraction. At each reflection,$25\%$ of the incident energy is reflected. The rays $AB$ and $A'B'$ undergo interference. The ratio ${I_{\max }}/{I_{\min }}$ is (in $: 1$)

Which of the following is a bacterial domain?

In order to calculate the map distance of genes on a chromosome,one must know the