A plano convex lens of refractive index $$\mu $$₁ and focal length ƒ₁ is kept in contact with another plano concave lens of refractive index $$\mu $$₂ and focal length ƒ₂. If the radius of curvature of their spherical faces is R each and ƒ₁ = 2ƒ₂, then $$\mu $$₁ and $$\mu $$₂ are related as -

In an electron microscope, the resolution that can be achieved is of the order of the wavelength of electrons used. To resolve a width of 7.5 × 10^–12 m, the minimum electron energy required is close to -

A string of length 1 m and mass 5 g is fixed at both ends. The tension in the string is 8.0 N. The string is set into vibration using an external vibrator of frequency 100 Hz. The separation between successive nodes on the string is close to -

A homogeneous solid cylindrical roller of radius R and mass M is pulled on a cricket pitch by a horizontal force. Assuming rolling without slipping, angular acceleration of the cylinder is -