Two cars are moving towards each other at the speed of $$50 \mathrm{~ms}^{-1}$$. If one of the cars blows a horn at a frequency of 250 Hz , the wave length of the sound perceived by the driver of the other car is
(Speed of sound in air $$=350 \mathrm{~ms}^{-1}$$)
A needle is lying at the bottom of a water tank of height 12 cm. The apparent depth of the needle measured by a microscope is 9 cm . If the water is replaced by a liquid of refractive index of 1.5 of same height, the distance through which the microscope has to be moved to focus the needle again is
Young's double slit experiment is conducted with monochromatic light of wavelength 5000$$\mathop A\limits^o $$, with slit separation of 3 mm and observer at 20 cm away from the slits. If a 1 mm transparent plate is placed infront of one of the slits, the fringes shift by 6 mm . The refractive index of the transparent plate is
A large number of positive charges each of magnitude $$q$$ are placed along the $$X$$-axis at the origin and at every 1 cm distance in both the directions. The electric flux through a spherical surface of radius 2.5 cm centred at the origin is