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# IIT-JEE-Physics–1998

Time : Three Hours                                                        Max. Marks : 100
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Instructions

1. This question paper is in two section and contains 8 pages. Section I has 40 objective type questions. Section II had 15 questions. There are no negative marks for wrong answers.
2. Answer section I only on the printed form on the third page of your answer book.
3. Answer problems of section II starting from page 4 of the answer book. All parts of a question must be answered sequentially at one place only.
4. Attempt all question/problems.
6. Use of logarithmic table is permitted.
7. Use of slide rule/calculate is not permitted.

Useful data
Acceleration due to gravity g = 10 m s–2
Speed of light in vacuum c = 3.0 × 108 ms–1
Planck’s constant h = 6.63 × 10–34 J s
Elementary charge e = 1.60 × 10–19 C ______________________________________________________________________

SECTION I

1. You must first transfer the code given here on top of this Section to your Answer Sheet In the appropriate box marked. Question Paper Code.
2. Answer Section I only on the printed form on the third page of your answer book by writing the appropriate letters (A), (B), (C) etc. against the question number in the table. Answers for Section I written in this space alone will be awarded marks.
3. Section I consists of 40 objective type questions.
5. Each question in this section carries 2 marks.
1A transistor is used in common emitter mode as an amplifier, then :
(A)the base emitter junction is forward biased

(B)the base emitter junction is reverse biased
(C)the input signal is connected in series with the voltage  applied to bias the base emitter junction.
(D)the input signal is connected in series with the voltage applied to bias the base collector junction.

2. Water from a tap emerges vertically downwards with an initial speed of 1.0 m/s. The cross-sectional area of tap is 10–4 m2. Assume that the pressure is constant throughout the stream of water and that the flow is steady, the cross-sectional area of stream 0.15 m below the tap is :
(A) 5.0 × 10–4 m2                                (B) 1.0 × 10–4 m2
(C) 5.0 × 10–5 m2                                (D) 2.0 × 10–5 m

3. A real image of a distant object is formed by a planoconvex lens on its principal axis. Spherical aberration:
(A) is absent
(B) is smaller if the curved surface of the lens faces the object
(C) is smaller if the plane surface of the lens faces the object
(D) is the same whichever side of the lens faces the object

4. Let v, vrms and vp respectively denote the mean speed, root mean square speed and most probable speed of the molecules in an ideal monoatomic gas at absolute temperature T. The mass of a molecule is m. Then :
(A) no molecule can have a energy greater then √2 Vrms
(B) no molecule can have speed less thenVp/√2
(C) Vp < V < Vrms
(D) the average kinetic energy of a molecule is 3/4 mvp2

5. A vessel contains a mixture of one mole of oxygen and two moles of nitrogen at 300K. The ratio of the average rotational kinetic energy per Omolecule to per N2molecule is:
(A) 1 : 1
(B) 1 : 2
(C) 2 : 1
(D) depends on the moment of inertia of the two molecules.

6. A string of length 0.4 ma and mass 10–2 Kg is tightly clamped at its ends. The tension in the string is 1.6N. Identical wave pulses are produced at one end at equal intervals of time Dt. The minimum value of  Dt, which allows constructive interference between successive pulses, is :
(A) 0.05 s                                                                              (B) 0.10 s
(C) 0.20 s                                                    (D) 0.40 s

7. Two particles, each of mass m and charge q, are attached to the two ends of a light rigid rod of length 2R. The rod is rotated at constant angular speed about a perpendicular axis passing through its centre. The ratio of the magnitudes of the magnetic moment of the system and its angular momentum about the centre of the rod is :
(A) q/2m                                                                               (B) q/m
(C) 2q/m                                                     (D) q/pm