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?

If two mirrors are kept at $${60^ \circ }$$ to each other, then the number of images formed by them is