Light of wavelength ' $\lambda$ ' is incident on a single slit of width ' $a$ ' and the distance between slit and screen is ' $D$ '. In diffraction pattern, if slit width is equal to the width of the central maximum then ' $D$ ' is equal to

In U.C.M., when time interval $\delta t \rightarrow 0$, the angle between change in velocity ( $\delta \mathbf{v}$ ) and linear velocity $(\boldsymbol{v})$ will be

A stretched string fixed at both ends has ' $m$ ' nodes, then the length of the string will be

A particle is performing a linear simple harmonic motion of amplitude ' $A$ '. When it is midway between its mean and extreme position, the magnitudes of its velocity and acceleration are equal. What is the periodic time of the motion?