The materials suitable for making electromagnets should have

A plano convex lens of refractive index $$1.5$$ and radius of curvature $$30$$ $$cm$$. Is silvered at the curved surface. Now this lens has been used to form the image of an object. At what distance from this lens an object be placed in order to have a real image of size of the object

A light ray is incident perpendicularly to one face of a $${90^ \circ }$$ prism and is totally internally reflected at the glass-air interface. If the angle of reflection is $${45^ \circ }$$, we conclude that the refractive index $$n$$

A particle of mass $$m$$ is attached to a spring (of spring constant $$k$$) and has a natural angular frequency $${\omega _0}.$$ An external force $$F(t)$$ proportional to $$\cos \,\omega t\left( {\omega \ne {\omega _0}} \right)$$ is applied to the oscillator. The time displacement of the oscillator will be proportional to