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Showing 2676 to 2700 of 3046 questions (page 108 of 122).

2676. The region near a p-n junction that is free of mobile charge carriers is called the

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

2677. The peak inverse voltage of a diode is the maximum reverse voltage it can withstand

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

2678. A bridge rectifier uses

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

2679. The output of an OR gate is low only when

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

2680. A rod moving at high speed along its length appears

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

2681. The rest mass of a photon is

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

2682. A photocell is a practical device based on

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

2683. 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

2684. The Paschen series of hydrogen lies in the

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

2685. Stimulated emission differs from spontaneous emission in that the emitted photon is

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

2686. The relation between the decay constant and the half life is

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

2687. In positron emission, the atomic number of the nucleus

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

2688. Control rods in a nuclear reactor are made of materials such as boron or cadmium because they

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

2689. Nuclear fusion requires extremely high temperatures in order to

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

2690. Radioisotopes are used in agriculture mainly to

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

2691. 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. equal masses D. equal numbers of molecules E. the same energy

2692. The number of moles present in 4.4 g of carbon dioxide is

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

2693. The percentage of oxygen by mass in water is about

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

2694. The complete combustion of one mole of methane requires oxygen of amount

A. 3 mol B. 2 mol C. 0.5 mol D. 1.5 mol E. 1 mol

2695. For solvent extraction to work, the two solvents used must be

A. both aqueous B. chemically identical C. immiscible with each other D. of the same density E. miscible with each other

2696. A Buchner funnel with a filter flask is used for

A. sublimation B. distillation C. crystallization D. titration E. filtration under suction

2697. The solution left after crystals have separated out during crystallization is called the

A. mother liquor B. eluent C. filtrate only D. supernatant gas E. distillate

2698. In thin layer chromatography, the stationary phase is supported on

A. a filter funnel B. a column of solvent C. a glass or plastic plate D. a strip of paper E. a metal wire

2699. A gas occupies 2 dm3 at 1 atm. At constant temperature and 4 atm its volume becomes

A. 1 dm3 B. 8 dm3 C. 4 dm3 D. 0.5 dm3 E. 2 dm3

2700. A gas occupying 273 cm3 at 273 K is heated at constant pressure to 546 K. Its new volume is

A. 136 cm3 B. 409 cm3 C. 273 cm3 D. 1092 cm3 E. 546 cm3

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