IIT JEE Physics Final Revision Set 39

1. 1. A 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 m²

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. 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 O2 molecule to per N2 molecule is:
(A) 1 : 1
(B) 1 : 2
(C) 2 : 1
(D) depends on the moment of inertia of the two molecules.

5.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/πm

Source: JEE 1998