EdgineerX

1626. Electromagnetic braking in trains relies on

A. compressed air alone B. friction pads only C. eddy currents induced in a moving metal disc or rail D. permanent magnets repelling E. chemical reaction

1627. A device that generates alternating current from mechanical rotation is called an

A. inverter B. electrolyser C. electromagnet D. amplifier E. alternator

1628. The induced emf in a coil is greatest when the rate of change of flux is

A. negative only B. maximum C. zero D. equal to the flux E. constant and small

1629. The inductive reactance of a coil of inductance L at frequency f is

A. f L B. 2 pi L divided by f C. L divided by 2 pi f D. 2 pi f L E. 1 divided by 2 pi f L

1630. A capacitor in a circuit

A. blocks direct current and passes alternating current B. passes both equally C. passes direct current and blocks alternating current D. blocks both E. behaves as a pure resistance

1631. In an LC circuit, energy oscillates between

A. the resistor and the source B. the magnetic field of the inductor and the electric field of the capacitor C. two capacitors only D. the source and earth E. heat and light

1632. In amplitude modulation, the quantity of the carrier wave that is varied in step with the signal is its

A. phase B. frequency C. wavelength only D. speed E. amplitude

1633. The rms value of an alternating current is defined as the steady direct current that would

A. produce the same heating effect in a given resistance B. have the same frequency C. have zero average D. have the same peak value E. flow for the same time

1634. Beyond the yield point, a metal specimen

A. becomes perfectly elastic B. obeys Hooke's law C. fractures immediately D. undergoes appreciable permanent deformation E. returns exactly to its original length

1635. Shear strain is measured as

A. the angle through which a face is displaced B. the change in volume divided by the original volume C. the change in length divided by the original length D. stress divided by strain E. force divided by area

1636. Conduction in a pure semiconductor arising from thermally generated electron hole pairs is described as

A. extrinsic B. intrinsic C. ionic D. superconducting E. metallic

1637. The output of an AND gate is high only when

A. the inputs differ B. all inputs are low C. all inputs are high D. any input is high E. one input is low

1638. A diode acts approximately as a closed switch when it is

A. in breakdown only B. unbiased C. at absolute zero D. reverse biased E. forward biased above its threshold voltage

1639. In a photoelectric experiment, increasing the intensity of light of a fixed frequency increases the

A. work function B. number of electrons emitted per second C. stopping potential D. threshold frequency E. maximum kinetic energy of the electrons

1640. A perfect black body is one that

A. transmits all radiation B. emits no radiation C. absorbs all incident radiation and is also the best emitter D. is always black in colour E. reflects all radiation

1641. The energy of the photon emitted when an electron falls from level n2 to level n1 equals

A. the sum of the two level energies B. zero C. the kinetic energy of the nucleus D. the ionization energy E. the difference between the two level energies

1642. Hard X-rays differ from soft X-rays in having

A. no charge B. lower frequency C. the same wavelength D. shorter wavelength and greater penetrating power E. longer wavelength and less penetrating power

1643. In a helium neon laser, the active medium is

A. a plasma of metal vapour B. a gas mixture C. a liquid dye D. a semiconductor junction E. a solid crystal

1644. The number of nucleons in a nucleus is given by its

A. mass number B. atomic number C. charge number D. binding energy E. neutron number

1645. Alpha particles have very low penetrating power because they

A. are heavy and doubly charged, so they ionize strongly and lose energy quickly B. are electromagnetic waves C. have no mass D. carry no charge E. travel at the speed of light

1646. On a graph of the number of undecayed nuclei against time, the curve is

A. a straight line with negative slope B. a horizontal line C. a parabola D. an exponential decay curve E. a sine wave

1647. The chief difficulty in disposing of high level nuclear waste is that it

A. dissolves in water instantly B. is chemically inert C. remains dangerously radioactive for very long times D. evaporates quickly E. cannot be transported

1648. The binding energy of a nucleus is the energy

A. of one photon B. of the emitted alpha particle C. stored in the electron shells D. released when the nucleus decays E. required to separate it completely into its individual nucleons

Physics