IIT JEE Physics Final Revision Set 41

1. The electron in a hydrogen atom makes a transition n1 ®n2 where n1 and n2 are the principal quantum numbers of two states. Assume the Bohr model to be valid. The time period of the electron in the initial state is eight times that in the final state. The possible values of n1 and n2 are :
(A) n1 = 4, n2 = 2 (B)n1 = 8, n2 = 2
(C) n1 = 8, n2 = 1 (D) n1 = 6, n2 = 3

2.A dielectric slab of thickness d is inserted in a parallel late capacitor whose negative plate is at x = 0 and positive plate is at x = 3d. The slab iis equidistant from the plates. The capacitor is given some charge. As x goes from 0 to 3d:
(A) the magnitude of the electric field remains the same
(B) the direction of the electric field remains the same
(C) the electric potential increases continuously
(D) the electric potential increases at first, then decreases and again increases.


3.The (x, y) coordinated of the corners of a square plate are (0, 0), (L, 0), (L, L) and (0, L). The edges of the plate are clamped and transverse standing waves re set up in it. If u (x, y) denotes the displacements of the plate at the point (x, y) at some instant of time, the possible expression (s) for u is (are) (a = positive constant):
(A) a cos (π x/2L) cos (π y/2L)
(B) a sin (π x/L) sin (π y/L)
(C) a sin (π x/L) sin (2π y/L)
(D) a cos (2π x/L) sin (π y/L)

4. A force F= K(y î + x ĵ) (where K is a positive constant) acts on a particle moving in the xy plane. Starting from the origin, the particle is taken along the positive x-axis to the point (a, 0) and then parallel to the y-axis to the point (a, a). The total work done by the force F on the particle is:
(A) –2Ka² (B) 2Ka²
(C) –Ka² (D) Ka²

5. A small square loop of wire of side l is placed inside a large square loop of wire of side L(L >> l). The loops are coplanar and their centres coincide. The mutual inductance of the system is proportional to :
(A) l/L (B) I²/L
(C) L/l (D) L²/l.


JEE 1998