A hollow sphere of volume V is floating on water surface with half immersed in it. What should be the minimum volume of water poured inside the sphere so that the sphere now sinks into the water
V
A parallel plate capacitor with air as the dielectric has capacitance C. A slab of dielectric constant K and having the same thickness as the separation between the plates is introduced so as to fill one-fourth of the capacitor as shown in the figure. The new capacitance will be
A coil of n number of turns is wound tightly in the form of a spiral with inner and outer radii a and b respectively. When a current of strength I is passed through the coil, the magnetic field at its centre is
A magnetic field exerts no force on
a magnet
an unmagnetised iron bar
a moving charge
stationary charge
In an L-C-R circuit inductance is changed from L to L/2.To keep the same resonance frequency, C should be changed to
2 C
4 C
Which one of the following graph represents the variation of maximum kinetic energy (Ek) of the emitted electrons with frequency v in photoelectric effect correctly?
A vessel of height 2 d is half filled with a liquid of refractive index and the other half with a liquid of refractive index n (the given liquids are immiscible). Then, the apparent depth of the inner surface of the bottom of the vessel (neglecting the thickness of the bottom of the vessel) will be
The two lenses of an achromatic doublet should have
equal powers
equal dispersive powers
equal ratio of their power and dispersive power
sum of the product of their powers and dispersive power equal to zero
The tip of a needle does not give a sharp image on a screen. This is due to
polarisation
interference
diffraction
None of these
C.
diffraction
As the size of tip of the needle is very small ( because its a point ) and it comes under the range of wavelength of light, so the ray coming from back side of needle ( i.e consider needle's tip just blocking a ray of light) will bend across the tip.
And hence on screen, that ray will also give brightness near so formed image of needle's tip, hence reducing the original sharpness of the needle's tip.
The tip of a needle does not give a sharp image, it is due to diffraction.
The truth table given below is for (A and B are the inputs, Y is the output)
A | B | Y |
0 | 0 | 1 |
0 | 1 | 1 |
1 | 0 | 1 |
1 | 1 | 0 |
NOR
AND
XOR
NAND