Physics

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Showing 951 to 975 of 1648 questions (page 39 of 66).

951. The back emf in a DC motor is greatest when the motor is

A. stalled B. just switched on C. disconnected D. reversed E. running at full speed

952. A step down transformer has 1000 turns in the primary and 100 in the secondary. If the primary voltage is 220 V, the secondary voltage is

A. 22 V B. 2200 V C. 110 V D. 2.2 V E. 220 V

953. The negative sign in Faraday's law expresses

A. Coulomb's law B. Lenz's law C. Ohm's law D. Ampere's law E. Gauss's law

954. Mutual inductance between two coils depends on

A. the current in the primary only B. the frequency of the supply only C. the voltage applied D. the relative geometry and number of turns of the coils E. the resistance of the secondary

955. The impedance of a series RLC circuit is

A. R + XL + XC B. R (XL - XC) C. sqrt(R2 + (XL - XC)2) D. sqrt(R2 + XL2 + XC2) E. R - XL + XC

956. The average value of a sinusoidal alternating current over one complete cycle is

A. twice the peak value B. the peak value C. zero D. 0.707 times the peak value E. 0.637 times the peak value

957. The frequency of the domestic AC mains supply in Pakistan is

A. 220 Hz B. 50 Hz C. 25 Hz D. 100 Hz E. 60 Hz

958. At resonance in a series RLC circuit, the impedance is

A. minimum and equal to R B. equal to XC C. infinite D. maximum and equal to XL E. zero

959. In a purely capacitive AC circuit, the current

A. lags the voltage by 90 degrees B. is zero C. is in phase with the voltage D. leads the voltage by 90 degrees E. leads by 180 degrees

960. The modulus that describes the deformation produced by a tangential force is

A. compressibility B. shear modulus C. Young's modulus D. Poisson's ratio E. bulk modulus

961. At absolute zero, a pure intrinsic semiconductor behaves as

A. a superconductor B. a metal C. a conductor D. a p-type material E. an insulator

962. A paramagnetic substance placed in a magnetic field is

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

963. The output ripple frequency of a half wave rectifier fed from a 50 Hz supply is

A. 150 Hz B. 25 Hz C. 100 Hz D. zero E. 50 Hz

964. A photodiode used as a light detector is normally operated in

A. breakdown as a regulator B. zero bias only C. the saturation region of a transistor D. reverse bias E. forward bias

965. A light emitting diode emits light when it is

A. cooled B. forward biased C. unbiased D. in breakdown E. reverse biased

966. The output of an XOR gate is high when

A. the inputs are different B. either input is low C. both inputs are high D. the inputs are the same E. both inputs are low

967. In a common emitter transistor amplifier, the current gain beta is the ratio of

A. collector current to base current B. base current to collector current C. emitter current to base current D. collector voltage to base voltage E. collector current to emitter current

968. According to special relativity, a moving clock runs

A. only at the speed of light B. backwards C. slower than a stationary clock D. faster than a stationary clock E. at the same rate

969. The energy equivalent of mass m is

A. m/c2 B. mc2 C. m2c D. mc E. (1/2)mc2

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

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

971. The wave nature of electrons was confirmed experimentally by

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

972. The momentum of a photon of wavelength lambda is

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

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

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

974. The Lyman series of hydrogen lies in the

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

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

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

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