Physics

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Showing 601 to 625 of 1648 questions (page 25 of 66).

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

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

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

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

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

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

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

605. Two parallel wires carrying current in the same direction

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

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

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

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

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

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

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

609. 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. 110 V C. 2.2 V D. 2200 V E. 220 V

610. The negative sign in Faraday's law expresses

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

611. Mutual inductance between two coils depends on

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

612. The impedance of a series RLC circuit is

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

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

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

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

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

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

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

616. In a purely capacitive AC circuit, the current

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

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

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

618. 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

619. A paramagnetic substance placed in a magnetic field is

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

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

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

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

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

622. A light emitting diode emits light when it is

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

623. The output of an XOR gate is high when

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

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

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

625. According to special relativity, a moving clock runs

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

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