201. The wavelength of light emitted by GaAs laser is 8670 x 10-10 m. If h = 6.626 x 10-34 Js, velocity of light = 3 x 108 m/s and eV = 1.602 x 10-19 J, the energy gap in GaAs is
202. Diamagnetic materials do not have permanent magnetic dipoles.
203. A piece of copper and another piece of Germanium are cooled from 30°C to 80 K. The resistance of
204. The direction of force an a conductor carrying current and lying in a magnetic field can be found by using
205. Assertion (A): Rochelle salt and Barium titanate are both ferroelectric. Reason (R): Ferroelectric materials exhibit hysteresis effect.
206. The units for electric dipole moment are
207. The temperature coefficient of resistivity of semiconductors is
208. Which of the following is used in automatic control of street lights?
209. A leaky dielectric has ∈r = ∈r' - j∈r". If a field E is applied, the current component in phase with E is proportional to ∈r".
210. Assertion (A): In ionic dielectrics, P = Pe + Pi.Reason (R): In ionic crystals, permanent electric dipole moment is zero.
211. The current flow in a semiconductor is due to
212. Assertion (A): Relative permittivity is determined by the atomic structure of the material.Reason (R): Absolute permittivity is determined by the atomic structure of the material.
213. Eddy current loss is
214. The dipole moment per unit volume P as a function of E for an insulator is
215. A good dielectric should have
216. Magnetic hysteresis phenomenon is explained by
217. The function of haemoglobin is?
218. The relation between thermal conductivity K (W/m/°C), heat flow density Q (watt/m2) and dT/dx (°C per metre) is
219. As per Matthiessen's rule, the total resistivity r of a conductor can be written as r = r i + aT, where r i and a are constants and T is absolute temperature. At very low temperatures
220. Consider the following statement: In case of a superconductor B = 0μr is highdiamagnetism is hightransition temperature varies with isotopic mass. Of the above statements
221. Assertion (A): In liquids and glassy substances, dielectric losses occur. Reason (R): The orientation polarization in many substances is frequency dependent.
222. A single layer air cored coil has n turns and inductance L. If a new coil is formed by having 2n turns while keeping the coil length and diameter the same, the new inductance is
223. The colour code on a carbon resistor is yellow-violet-orange. The value of resistance is
224. A dielectric of relative permittivity ∈r is subjected to a homogeneous electric field E. The dipole moment P per unit volume is given by
225. Which of these has the highest dielectric strength?