2. The fringe separation in young's double slits experiment is constant. What about in a plane transmission grating experiment? Is the fringe separation also constant?
3. Why is the wavelength of a stationary wave fromed by a string when one end is free to move equal to 4 L (one loop)? Is it because the reflected wave does not undergo any phase change, therefore it overlaps with the wave?
4. Flash lamps used by professional photographers can find object distances by using infrared waves so as to adjust the flash output. Which of the following is/are the reason(s) of using infrared waves instead of ultrasonic waves in such flash lamps?
'Objects to be photographed will usually emit infrared waves' Why is this statement false?
5. Light travels in media M1 and M2 with speeds v1 and v2 respectively. When light travelling from media M1 strikes a boundary between the two media with angle of incidence i, it suffers total internal reflection. This indicates that
2) sin i is less than v1 / v2
3) sin i is greater than v2 / v3
Are these 2 statements correct? Can some1 explain it to me?
6. In a Young's double-slit experiment using a light of wavelength 600nm, a thin sheet of mica (n=1.5) is placed in from of one of the slits and the centre of the fringe pattern is displaced through 4 fringe widths. What is the thinkness of the mica?
I don't even know what it's talking about. Can some1 give me a diagram showing the set-up of that experiment?
thanks
更新1:
7. (A question related to gas) CE 1990 Q20 A flask with water at 80 C inside (with a thermometer) is connected to a vacuum pump. Which of the following will happen when thevacuum pump is switched on?
更新2:
Why the temperature reading is not constant? Since the vacuum pump is switched on, the number of molecules inside the flask should be decreasing. By pV=nRT, the pressure is thereofre lowered and the water can boil. Why does the temperature change as well?