The magnifying power of a telescope with tube 60 cm is 5. What is the focal length of its eye piece ?

At time t = 0 magnetic field of 1000 Gauss is passing perpendicularly through the area defined by the closed loop shown in the figure. If the magnetic field reduces linearly to 500 Gauss, in the next 5s, then induced EMF in the loop is :

The critical angle of a medium for a specific wavelength, if the medium has relative permittivity 3 and relative permeability $${4 \over 3}$$ for this wavelength, will be :

Three charged particle A, B and C with charges –4q, 2q and –2q are present on the circumference of a circle of radius d. the charged particles A, C and centre O of the circle formed an equilateral triangle as shown in figure. Electric field at O along x-direction is :