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Showing 1901 to 1925 of 3046 questions (page 77 of 122).

1901. The output of an OR gate is low only when

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

1902. A rod moving at high speed along its length appears

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

1903. The rest mass of a photon is

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

1904. A photocell is a practical device based on

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

1905. The difference between excitation and ionization of an atom is that ionization

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

1906. The Paschen series of hydrogen lies in the

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

1907. Stimulated emission differs from spontaneous emission in that the emitted photon is

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

1908. The relation between the decay constant and the half life is

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

1909. In positron emission, the atomic number of the nucleus

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

1910. 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. slow down neutrons D. produce neutrons E. absorb neutrons strongly

1911. Nuclear fusion requires extremely high temperatures in order to

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

1912. Radioisotopes are used in agriculture mainly to

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

1913. Avogadro's law states that equal volumes of all gases under the same conditions contain

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

1914. The number of moles present in 4.4 g of carbon dioxide is

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

1915. The percentage of oxygen by mass in water is about

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

1916. The complete combustion of one mole of methane requires oxygen of amount

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

1917. For solvent extraction to work, the two solvents used must be

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

1918. A Buchner funnel with a filter flask is used for

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

1919. The solution left after crystals have separated out during crystallization is called the

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

1920. In thin layer chromatography, the stationary phase is supported on

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

1921. A gas occupies 2 dm3 at 1 atm. At constant temperature and 4 atm its volume becomes

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

1922. A gas occupying 273 cm3 at 273 K is heated at constant pressure to 546 K. Its new volume is

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

1923. Standard temperature and pressure are defined as

A. 0 K and zero pressure B. 273 K and 760 mm of mercury only at the equator C. 373 K and 1 atm D. 298 K and 1 atm E. 273.15 K and 1 atm

1924. The volume occupied by 0.5 mol of any ideal gas at STP is

A. 5.6 dm3 B. 11.2 dm3 C. 2.24 dm3 D. 22.4 dm3 E. 44.8 dm3

1925. A hydrogen bond is typically

A. weaker than a covalent bond but stronger than a London force B. stronger than a covalent bond C. of zero energy D. weaker than a London dispersion force E. identical to an ionic bond

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