11. 12. A parallel beam of monochromatic light is incident on a narrow rectangular slit of width 1mm. When the diffraction pattern in seen on a screen placed at a distance of 2m, the width of principal maxima is found to be 2.5mm. The wavelength of light is (a) 6250 (b) 6200 (c) 5890 (d) 6000 The figure shows the initial position of a point source of lights, a detector D and lens L. Now at t = 0, all three starts moving towards right with different velocity as shown in figure. The times at which detector receives the maximum light, is (Assume that the detector is initially just touching the lens). 3cms L lcms D 3cms focal length = 0.9cm 10cm (a) 5s and 10s (b) 0.5s and 4.5s (c) 2s and 3s (d) Only 10s 13. Figure shows the anode potential vs photo-current graph when photons of 6 eV are incident on cathode in a photoelectric experiment set-up. In the same experimental set-up, if photons of 8 eV and same intensity are incident on cathode, then anode-potential vs photo-current graph will be (assume 100% efficiency of photons to eject photo-electrons in both cases) photocurrent I -3V (A) -3V O anode potential shiksha (B) -3V (C) (D) -3V + -3V 14. A sound source is located somewhere along the x-axis. Experiment shows that the same wavefront simultaneously reaches listeners at x = -10m and x = +4.0m. A third listener is positioned along the positive y-axis. What is y-coordinate (in m) if the same wavefront reaches at him at the same instant it does the first two listeners? (a) 40 (b) 3 (c) 7 (d) 30 15. The temperature-entropy diagram of a reversible engine cycle is given in the figure. Its efficiency is: (a) 1/2 T 2T (b) 11/14 . S So 250 (c) 3 (d) 23 16. At t < 0, the capacitor is charged and the switch is opened. At t = 0 the switch is closed. The shortest time T at which the charge on the capacitor will be zero is given by: Qo C TH (a) LC 3 (b) -LC 2 (c) VLC (d) 2VLC