If a ray of light in denser medium strikes a rarer medium at angle of incidence $$i$$, the angles of reflection and refraction are $$r$$ and $$r^{\prime}$$ respectively. If the reflected and refracted rays are at right angles to each other, the critical angle for the given pair of media is

A spring has a certain mass suspended from it and its period for vertical oscillations is '$$T_1$$'. The spring is now cut in to two equal halves and the same mass is suspended from one of the halves. The period of vertical oscillations is now '$$\mathrm{T}_2$$'. The ratio $$\mathrm{T}_1 / \mathrm{T}_2$$ is

When photons of energies twice and thrice the work function of a metal are incident on the metal surface one after other, the maximum velocities of the photoelectrons emitted in the two cases are $$\mathrm{v}_1$$ and $$\mathrm{v}_2$$ respectively. The ratio $$\mathrm{v}_1: \mathrm{v}_2$$ is

A simple pendulum of length $$2 \mathrm{~m}$$ is given a horizontal push through angular displacement of $$60^{\circ}$$. If the mass of bob is 200 gram, the angular velocity of the bob will be (Take Acceleration due to gravity $$=10 \mathrm{~m} / \mathrm{s}^2$$ ) $$\left(\sin 30^{\circ}=\cos 60^{\circ}=0.5, \cos 30^{\circ}=\sin 60^{\circ}=\sqrt{3} / 2\right)$$