
question_answer1) A conductor is bent in the form of concentric semicircles as shown in the figure. The magnetic field at the point O is
A) Zero done
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B) \[\frac{{{\mu }_{0}}l}{6a}\] done
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C) \[\frac{{{\mu }_{0}}l}{a}\] done
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D) \[\frac{{{\mu }_{0}}l}{4a}\] done
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question_answer2) When a dc voltage of 200 V is applied to a coil of selfinductance \[(2\sqrt{3}\,/\pi )\]H, a current of 1 A flows through it. But by replacing dc source with ac source of 200 V, the current in the coil is reduced to 0.5 A. Then the frequency of ac supply is
A) \[100\text{ }Hz~\] done
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B) \[75\text{ }Hz\] done
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C) \[60\text{ }Hz\] done
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D) \[50\text{ }Hz\] done
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question_answer3) Two radioactive substances X and Y emit a current \[\alpha \]and \[\beta \]particles respectively. Their disintegration constants are in the ratio 2:3. To have equal probabilities of getting emission of a and p particles, the ratio of number of atoms of X to that of Y at any time instant is
A) \[2\text{:}3\] done
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B) \[3:2~\] done
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C) \[e:1\] done
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D) \[\left( e1 \right):1\] done
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question_answer4) An object is placed in front of a spherical mirror of focal length f. If x and X' respectively represent the distance of the object and the image from the focus, then
A) \[f=x+x'\] done
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B) \[{{f}^{^{2}}}=x\,\,x'\] done
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C) \[f=\left \left. xx' \right \right.\] done
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D) f = x ? x' depending upon whether image is real or virtual done
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question_answer5) In a certain particle accelerator, electrons emerge in pulses at the rate of 250 pulses per second. Each pulse is of duration of 200 ns and the electrons in the pulse constitute a current of 250 mA. The number of electrons delivered by the accelerator per pulse Is
A) \[8.00\text{ }\times \text{ }{{10}^{10}}~\] done
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B) \[5.00\text{ }\times \text{ }{{10}^{8}}\] done
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C) \[3.13\text{ }\times \text{ }{{10}^{11}}\] done
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D) \[9.60\text{ }\times \text{ }{{10}^{10}}\] done
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question_answer6) A solenoid of 0.4 m length with 500 turns carries a current of 3 A. A coil of 10 turnsand of radius 0.01 m carries a current of 0.4 A. The torque required to hold the coil with its axis at right angle to that of solenoid in the middle part of it, is
A) \[6{{\pi }^{2}}\times {{10}^{7}}N\,\,\,m\] done
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B) \[3{{\pi }^{2}}\times {{10}^{7}}N\,\,\,m\] done
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C) \[9{{\pi }^{2}}\times {{10}^{7}}N\,\,\,m\] done
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D) \[12{{\pi }^{2}}\times {{10}^{7}}N\,\,\,m\] done
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question_answer7) Uniform magnetic field 6 is directed vertically upwards and 3 wires of equal length L, carrying equal current l are lying in a horizontal plane such that the first one is along north, second one along northeast and the third one at \[{{60}^{{}^\circ }}\] north of east. Force exerted by magnetic field B on them is
A) zero on the first done
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B) \[\frac{BIL}{\sqrt{2}}\]on the second done
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C) \[\sqrt{3}\frac{BIL}{\sqrt{2}}\]on the third done
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D) BIL on all of them done
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question_answer8) A charged particle enters into a region which offers a resistance against its motion and uniform magnetic field exists in the region. The particle traces a spiral path as shown in the figure. Which of the following statements is correct?
A) Component of the magnetic field in the plane of spiral is zero. done
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B) Particle enters in the region at Q. done
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C) If the magnetic field is outward then the particle is positively charged. done
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D) All of the above. done
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question_answer9) Two identical charged spheres suspended from a common point by two massless strings of length l are initially a distance\[d(d<<l)\] apart because of their mutual repulsion. The charge begins to leak from both the spheres at a constant rate. As a result the charges approach each other with a velocity v. Then as a function of distance x between them
A) \[v\,\,\propto \,\,{{x}^{1/2}}\] done
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B) \[v\,\,\propto \,\,{{x}^{1}}\] done
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C) \[v\,\,\propto \,\,{{x}^{1/2}}\] done
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D) \[v\,\,\propto \,\,x\] done
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question_answer10) A particle of mass 40 mg and carrying a charge \[5\times {{10}^{9}}\] C is moving towards a fixed charge of magnitude \[{{10}^{8}}\] C. When it is at a distance of 10 cm from the fixed charge, it has a velocity of 50 cm/s. At what distance from the fixed charge will the particle come momentarily to rest?
A) \[1.3\,\times {{10}^{3}}\,\,\,m\] done
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B) \[1.9\,\times {{10}^{3}}\,\,\,m\] done
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C) \[3.9\,\times {{10}^{2}}\,\,\,m\] done
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D) \[4.7\,\times {{10}^{2}}\,\,\,m\] done
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question_answer11) A galvanometer has a resistance of 30 \[\Omega \] and a current of 2.0 mA gives full scale deflection. How will you convert this galvanometer into a voltmeter of 0.2 volt range?
A) 700\[\Omega \]. resistance should be connected parallel to the galvanometer. done
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B) 70 \[\Omega \] resistance should be connected parallel to the galvanometer. done
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C) 700\[\Omega \], resistance should be connected in series with the galvanometer. done
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D) 70 \[\Omega \] resistance should be connected in series with the galvanometer. done
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question_answer12) A resistor R and \[2\mu F\] capacitor in series is connected through a switch to 200 V direct supply. Across the capacitor is a neon bulb that lights up at 120 V. Find the value of R to make the bulb light up 5 s after the switch has been closed. \[\left( {{\log }_{10}}2.5=0.4 \right)\]
A) \[1.3\times {{10}^{4}}\Omega \] done
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B) \[1.7\times {{10}^{5}}\Omega \] done
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C) \[2.7\times {{10}^{6}}\Omega \] done
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D) \[3.3\times {{10}^{7}}\Omega \] done
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