74. In an astronomical telescope in normal adjustment a straight black line of length L is drawn on inside part of objective lens. The eyepiece forms a real image of this line. The length of this image is l. The magnification of the telescope is :

61. The refracting angle of a prism is ’ A ’, and refractive index of the material of the prism is cot(A/2). The angle of minimum deviation is :

60. A beam of light consisting of red, green and blue colours is incident on a right angled prism. The refractive index of the material of the prism for the above red, green and blue wavelengths are 1.39, 1.44 and 1.47 , respectively. The prism will :

60. A beam of light consisting of red, green and blue colours is incident on a right angled prism. The refractive index of the material of the prism for the above red, green and blue wavelengths are 1.39, 1.44 and 1.47 , respectively. The prism will :

48. Two identical thin plano-convex glass lenses (refractive index 1.5) each having radius of curvature of 20 cm are placed with their convex surfaces in contact at the centre. The intervening space is filled with oil of refractive index 1.7. The focal length of the combination is ?

A parallel plate air capacitor of capacitance C is connected to a cell of emf V and then disconnected from it. A dielectric slab of dielectric constant K, which can just fill the air gap of the capacitor, is now inserted in it. Which of the following is incorrect ?

A parallel plate air capacitor has capacity ’ C ’ distance of separation between plates is ’ d ’ and potential difference ’ V ’ is applied between the plates. Force of attraction between the plates of the parallel plate air capacitor is ?

If potential (in volts) in a region is expressed as V (x, y, z) = 6xy − y + 2yz, the electric field (in N/C ) at point (1, 1, 0) is ?

The electric field in a certain region is acting radially outward and is given by E = Aa. A charge contained in a sphere of radius ’ a ’ centered at the origin of the field, will be given by ?