1. 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 is l.t. V is l.t. Vrms
(D) the average kinetic energy of a molecule is 3/4 mvp²
2. 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) 0.05s (B) 0.10 s
(C) 0.20 s
(D) 0.40 s
3.A ray of light travelling in a transparent medium falls on a surface separating the medium from air at an angle of incidence 450. The ray undergoes total internal reflection. If n is the refractive index of the medium with respect to air, select the possible value(s) of n from the following :
(A) 1.3 (B) 1.4
(C) 1.5 (D) 1.6
4. Let mp be the mass of proton, mn the mass of neutron. M1 the mass of 20/10 Ne nucleus and M2 the mass of 40/20 Ca nucleus. Then :
(A) M2 = 2M1 (B) M2 > 2M1
(C) M2 < 2M1 (D) M1 < 10 (mn + mp)
5. A parallel monochromatic beam of light is incident normally on a narrow slit. A diffraction pattern is formed on a screen placed perpendicular to the direction of the incident beam. At the first minimum of the diffraction pattern, the phase difference between the rays coming from the two edges of the slit is:
(A) 0 (B) π /2
(C) π (D) 2π
Source. 1998 JEE
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