The resistivity of iron at 20°C is 9.71 × 108 The resistivity of silver at 20°C is 1.59 × 108 The resistivity of Glass at 20°C is 1.10 × 109 The resistivity of nichrome at 20°C is 100 × 108 Hence silver is the least resistive material in the given option.
A single-phase induction motor with only one winding on the stator cannot produce any starting torque. Hence, some extra arrangement is required to start the motor. In the running condition, the motor is capable of developing the torque with only one winding on the stator. The simplest method of starting is to provide an auxiliary winding on the stator in addition to the main winding. The two windings are placed in the stator with their axes displaced by 90 electrical degrees in space.
While estimating the overhead lines, the first and last pole is always earth connected and after every 3rd electrical pole, the fourth pole is earthed. Therefore, the approximate number of required ground set = 4
Skin Effect The steady direct current distributes itself uniformly over the whole section of a conductor but the alternating current does not distribute uniformly rather than it tends to concentrate near the surface of a conductor. In fact in the AC system, no current flows through the core and the entire current is concentric at the surface regions. This phenomenon is called skin effect. The skin effect causes the effective resistance of the conductor to increase with the frequency of the current. The skin effect is due to eddy currents set up by the AC current. The skin effect has practical consequences in the design of radiofrequency and microwave circuits and to some extent in AC electrical power transmission and distribution systems.
EXAMIANS