Physics

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Showing 351 to 375 of 1648 questions (page 15 of 66).

351. Below its critical temperature, the electrical resistance of a superconductor is

A. very large B. slightly reduced C. zero D. negative E. temperature dependent and rising

352. In a series circuit, the quantity that is the same through every component is

A. potential difference B. current C. power D. resistance E. charge stored

353. The direction of force on a current carrying conductor in a magnetic field is given by

A. Fleming's right hand rule B. Fleming's left hand rule C. Lenz's law D. Coulomb's law E. the corkscrew rule for potential

354. A charged particle of mass m and charge q entering a magnetic field B perpendicularly with speed v moves in a circle of radius

A. mv/qB B. qB/mv C. mvB/q D. qvB/m E. mq/vB

355. Two parallel wires carrying current in the same direction

A. repel each other B. attract each other C. exert no force D. rotate about each other E. attract only if the currents are unequal

356. Faraday's law of induction states that the induced emf is proportional to the

A. magnetic flux B. rate of change of magnetic flux C. current in the coil D. resistance of the coil E. area of the coil only

357. The peak emf produced by an AC generator with N turns, area A, rotating at angular frequency omega in field B is

A. NAB B. NAB omega C. NAB/omega D. NA omega E. AB omega

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

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

359. 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. 2200 V B. 220 V C. 22 V D. 2.2 V E. 110 V

360. The negative sign in Faraday's law expresses

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

361. Mutual inductance between two coils depends on

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

362. The impedance of a series RLC circuit is

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

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

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

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

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

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

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

366. In a purely capacitive AC circuit, the current

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

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

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

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

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

369. A paramagnetic substance placed in a magnetic field is

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

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

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

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

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

372. A light emitting diode emits light when it is

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

373. The output of an XOR gate is high when

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

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

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

375. According to special relativity, a moving clock runs

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

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