L27. Two point charges each of mass m and charge g are suspended by strings of length / from a common point. Find the value of g for which the angle made by the strings at the common point is 90. 1.27. From the construction shown, mg = tan 45* =1 AXE - 212 or, Q = 8x Egl mg 4 TIC . 212 VEL mg1.42. Obtain the expression for the orbital frequency for an electron moving in a circular orbit normal to a uniform magnetic field of flux density B, Wh/m". Compute its value for By equal to 5 x 1077, 1.42. Equating the magnetic force to the centripetal force, we have 2 my evBo = , Or, /= eBo rt eBo eBo Orbital frequency = 2am For Bo = 5 x10,1.7578x101 1 orbital frequency = X 5x10 5 = 1.3988 x10 Hz = 1.3988 MHz.1.43. A magnetic field B = By(a, + 2a, - 4a,) exists at a point. What should be the electric field at that point if the force experienced by a test charge moving with a velocity v = 10(3a, - a, + 2a,) is to be zero?