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Showing 1251 to 1275 of 3046 questions (page 51 of 122).

1251. The peak to peak value of an alternating voltage of peak value V0 is

A. V0 B. V0/sqrt(2) C. V0/2 D. 2V0 E. V0 sqrt(2)

1252. A radio receiver is tuned to a station by adjusting the

A. capacitance of the tuning circuit B. loudspeaker impedance C. supply voltage D. aerial length only E. resistance in the circuit

1253. Electrical power is transmitted at high voltage over long distances in order to

A. increase the resistance of the line B. avoid using transformers C. reduce the voltage at the consumer end directly D. increase the current E. reduce the current and hence the I squared R loss

1254. The bulk modulus of a material relates

A. strain to time B. shear stress to shear strain C. volume stress to volume strain D. tensile stress to longitudinal strain E. stress to temperature

1255. A material that can be drawn into thin wires is described as

A. ductile B. amorphous C. malleable D. elastic only E. brittle

1256. Doping a semiconductor with a trivalent impurity produces

A. an n-type semiconductor B. an insulator C. an intrinsic semiconductor D. a p-type semiconductor E. a conductor

1257. In a metallic conductor, the valence and conduction bands

A. have a gap of 1.1 eV B. overlap or the valence band is partly filled C. are widely separated D. are both completely full E. are both completely empty

1258. The region near a p-n junction that is free of mobile charge carriers is called the

A. channel B. depletion region C. conduction band D. potential well E. forbidden gap

1259. The peak inverse voltage of a diode is the maximum reverse voltage it can withstand

A. without breaking down B. while conducting C. in forward bias D. at zero current E. during rectification only in a bridge circuit

1260. A bridge rectifier uses

A. a centre tapped transformer and one diode B. two diodes C. three diodes D. one diode E. four diodes

1261. The output of an OR gate is low only when

A. one input is high B. the inputs are equal C. both inputs are high D. both inputs are low E. the inputs differ

1262. A rod moving at high speed along its length appears

A. longer than its rest length B. bent C. shorter than its rest length D. unchanged in length E. of zero length at any speed

1263. The rest mass of a photon is

A. h/c B. zero C. 1.66 x 10^-27 kg D. equal to that of an electron E. infinite

1264. A photocell is a practical device based on

A. nuclear fission B. pair production C. the Compton effect D. the photoelectric effect E. the Doppler effect

1265. The difference between excitation and ionization of an atom is that ionization

A. involves only the nucleus B. produces no radiation C. requires less energy D. occurs only in molecules E. removes the electron completely from the atom

1266. The Paschen series of hydrogen lies in the

A. visible region B. ultraviolet region C. X-ray region D. infrared region E. microwave region

1267. Stimulated emission differs from spontaneous emission in that the emitted photon is

A. emitted in a random direction B. in phase and in the same direction as the incident photon C. of lower energy D. unpolarized E. of longer wavelength

1268. The relation between the decay constant and the half life is

A. lambda = T B. lambda = T/0.693 C. lambda = 0.693/T D. lambda = 1/T2 E. lambda = 2T

1269. In positron emission, the atomic number of the nucleus

A. decreases by 4 B. increases by 1 C. decreases by 1 D. increases by 2 E. is unchanged

1270. Control rods in a nuclear reactor are made of materials such as boron or cadmium because they

A. reflect neutrons B. conduct heat well C. produce neutrons D. slow down neutrons E. absorb neutrons strongly

1271. Nuclear fusion requires extremely high temperatures in order to

A. melt the fuel B. increase the nuclear force range C. reduce the mass defect D. overcome the electrostatic repulsion between nuclei E. ionize the surrounding air

1272. Radioisotopes are used in agriculture mainly to

A. trace the uptake of nutrients by plants B. reduce the need for water C. sterilize soil completely D. replace fertilizers E. increase rainfall

1273. Avogadro's law states that equal volumes of all gases under the same conditions contain

A. equal numbers of atoms B. the same density C. the same energy D. equal numbers of molecules E. equal masses

1274. The number of moles present in 4.4 g of carbon dioxide is

A. 0.01 B. 0.2 C. 0.44 D. 1.0 E. 0.1

1275. The percentage of oxygen by mass in water is about

A. 11.1% B. 88.9% C. 50% D. 66.7% E. 33.3%

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