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Showing 601 to 625 of 3046 questions (page 25 of 122).

601. Photoemission does not occur if the incident light has a frequency below the

A. cut off wavelength B. threshold frequency C. stopping potential D. Compton frequency E. Rydberg frequency

602. The wave nature of electrons was confirmed experimentally by

A. Millikan's oil drop experiment B. the Davisson and Germer electron diffraction experiment C. Rutherford's scattering experiment D. the photoelectric experiment E. Michelson's interferometer

603. The momentum of a photon of wavelength lambda is

A. h lambda B. h/lambda C. lambda/h D. hc/lambda E. h/c lambda

604. The work function of a metal is commonly expressed in

A. joules only B. electron volts C. watts D. coulombs E. hertz

605. The Lyman series of hydrogen lies in the

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

606. The energy of the electron in the second Bohr orbit of hydrogen is

A. -13.6 eV B. -6.8 eV C. -3.4 eV D. -1.51 eV E. -0.85 eV

607. In alpha decay, the mass number and atomic number of the nucleus change by

A. -4 and -2 B. -2 and -4 C. -4 and +2 D. 0 and -1 E. -1 and 0

608. The SI unit of radioactive activity is

A. curie B. becquerel C. gray D. sievert E. roentgen

609. Radiocarbon dating of organic remains uses the isotope

A. carbon 12 B. carbon 13 C. carbon 14 D. uranium 238 E. potassium 40

610. Nuclear forces are

A. long range and charge dependent B. short range and charge independent C. identical to electrostatic forces D. weaker than gravitational forces E. effective only between protons

611. The minimum mass of fissile material required to sustain a chain reaction is called the

A. atomic mass B. critical mass C. mass defect D. binding mass E. threshold mass

612. Cobalt 60 is used in medicine mainly as a source of

A. alpha particles B. beta particles C. gamma rays for radiotherapy D. neutrons E. X-rays

613. A radioactive sample of initial activity A0 has a half life T. Its activity after time 4T is

A. A0/4 B. A0/8 C. A0/16 D. A0/32 E. A0/2

614. The molar mass of carbon dioxide is

A. 28 g mol-1 B. 32 g mol-1 C. 44 g mol-1 D. 48 g mol-1 E. 12 g mol-1

615. One atomic mass unit is equal to

A. 1.661 x 10^-27 kg B. 1.661 x 10^-24 kg C. 6.02 x 10^-23 kg D. 9.1 x 10^-31 kg E. 1.6 x 10^-19 kg

616. The total number of atoms in one mole of methane is

A. 6.02 x 10^23 B. 1.204 x 10^24 C. 3.01 x 10^24 D. 2.41 x 10^24 E. 5 x 10^23

617. The molecular formula of a compound is related to its empirical formula by

A. division by a whole number B. multiplication by a whole number C. addition of a constant D. the ratio of densities only E. subtraction of hydrogen

618. Percentage yield is calculated as

A. theoretical yield divided by actual yield times 100 B. actual yield divided by theoretical yield times 100 C. actual yield minus theoretical yield D. mass of reactants divided by mass of products E. moles of product times 100

619. Distillation under reduced pressure is used for liquids that

A. have very low boiling points B. decompose at their normal boiling points C. are immiscible with water D. are highly volatile E. form no vapour

620. A desiccator is used to

A. heat substances strongly B. keep substances free from moisture while cooling C. distil liquids D. weigh precipitates E. dissolve solids

621. A sharp and constant melting point is used as a criterion of

A. solubility B. purity C. volatility D. density E. conductivity

622. In descending paper chromatography, the solvent moves

A. upwards by capillary action B. downwards under gravity C. horizontally only D. in a circle E. in the vapour phase only

623. At constant volume, the pressure of a fixed mass of gas is directly proportional to its

A. volume B. absolute temperature C. molar mass D. density E. number of collisions only

624. The volume occupied by 2 moles of an ideal gas at STP is

A. 11.2 dm3 B. 22.4 dm3 C. 44.8 dm3 D. 24.0 dm3 E. 5.6 dm3

625. Real gases deviate most from ideal behaviour at

A. high temperature and low pressure B. low temperature and high pressure C. high temperature and high pressure D. low temperature and low pressure E. standard conditions

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