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Showing 701 to 725 of 1648 questions (page 29 of 66).

701. The resistance of a conductor of length L, area of cross section A and resistivity rho is

A. rho L A B. A / rho L C. L / rho A D. rho L / A E. rho A / L

702. In the resistor colour code, the fourth band indicates

A. the multiplier B. the first digit C. the temperature coefficient D. the tolerance E. the power rating

703. The magnetic field at a perpendicular distance r from a long straight wire carrying current I is

A. mu_0 I / (2r) B. mu_0 I / (2 pi r) C. mu_0 I r D. mu_0 I / r2 E. 2 pi mu_0 I r

704. The force on a 2 m length of wire carrying 3 A placed perpendicular to a 0.5 T field is

A. 6 N B. 12 N C. 3 N D. 1.5 N E. 0.75 N

705. A loudspeaker converts electrical energy into sound using

A. the photoelectric effect B. electrostatic attraction C. thermal expansion D. piezoelectric heating only E. the force on a current carrying coil in a magnetic field

706. A diamagnetic substance in a magnetic field is

A. weakly repelled B. weakly attracted C. strongly attracted D. unaffected E. permanently magnetized

707. Flux linkage through a coil of N turns each enclosing flux Phi is

A. N/Phi B. N Phi C. N2 Phi D. Phi E. Phi/N

708. A generator converts

A. chemical to electrical energy B. light to electrical energy C. heat to electrical energy D. mechanical energy to electrical energy E. electrical energy to mechanical energy

709. Self induction in a coil always

A. opposes the change in current B. assists the change in current C. increases the resistance D. stops the current E. reverses the current

710. A transformer with 500 primary turns and 2500 secondary turns supplying 220 V to the primary gives a secondary voltage of

A. 2500 V B. 220 V C. 44 V D. 550 V E. 1100 V

711. 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)

712. 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

713. 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

714. 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

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

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

716. 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

717. 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

718. 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

719. 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

720. A bridge rectifier uses

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

721. 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

722. 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

723. 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

724. 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

725. 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

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