Torque acting on a rectangular coil carrying current ' $l$ ' situated parallel to magnetic field of induction ' $B$ ', having number of turns ' $n$ ' and area ' $A$ ' is

A force $(F)=-5 \hat{\mathbf{i}}-7 \hat{\mathbf{j}}+3 \hat{\mathbf{k}}$ acting on a particle causes a displacement $(s)=3 \hat{\mathbf{i}}-2 \hat{\mathbf{j}}+a \hat{\mathbf{k}}$ in its own direction. If the work done is 14 J , then the value of ' $a$ ' is

When the electron in hydrogen atom jumps from fourth Bohr orbit to second Bohr orbit, one gets the

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