Sum of infinite number of terms of GP is 20 and sum of their square is 100. The common ratio of GP is

If the chord y = mx + 1 of the circle $${x^2}\, + \,{y^2} = 1$$ subtends an angle of measure $${45^ \circ }$$ at the major segment of the circle then value of m is :

The energy band gap is maximum in

Which of the following are not electromagnetic waves?