VITEEE 2015 :: Physics :: General questions

• Physics - General questions

The ratio of the volume occupied by an atom to the volume of the nucleus is 

Answer:

Explanation:

As we knows, radius of an atom, 

$\gamma_{A}\approx 10^{-10}m$

 radius of nucleus,   $\gamma_{B}\approx 10^{-15}m$

 So, ratio of their volumes

$\frac{V_{A}}{V_{N}}=\frac{\frac{4}{3}\pi r^{3}_{A}}{\frac{4}{3}\pi r^{3}_{N}}=\left(\frac{r_{A}}{I_{N}}\right)^{3}=\left(\frac{10^{-10}}{10^{-15}}\right)^{3}$

 $V_{A}:V_{N}=10^{15}:1$

When sunlight is scattered by atmospheric atoms and molecules the amount of scattering of light of wavelength 880nm is A. Then, the  amount of scattering  of light of wavelength 330nm is approximately

Answer:

Explanation:

From Rayleigh's law of scattering, intensity

$I\propto\frac{1}{\lambda^{4}}$

 $\therefore$    $\frac{I_{1}}{I_{2}}\propto\left(\frac{\lambda_{2}}{\lambda_{1}}\right)^{4}$

$\Rightarrow\frac{I_{1}}{I_{2}}=\left(\frac{330}{880}\right)^{4}=\left(\frac{3}{8}\right)^{4}=\frac{81}{4096}$

${I_{2}}=(\frac{4096}{81})$Å =(50.557)Å

Pick out the wrong statement

Answer:

Explanation:

An electromagnetic wave is the wave radiated by an accelerated charge and propagates through space as coupled electric and magnetic field. These fields are oscillating  perpendicular to each other

An electromagnetic wave propagating along north lies its electric field vertically upward.The magnetic field vector points towards

Answer:

Explanation:

 As the electromagnetic wave is the crossed field of electric and magnetic waves, so the direction of propagation of EM  wave is the direction of vector  E x B. Here E is upward and (Ex B) is towards the north. So, from right-hand thumb rule B will be along east 

Two polaroids are kept crossed on top each other. If one of them is rotated an angle 60°, the percentage of incident light now transmitted through the system is 

Answer:

Explanation:

Let the intensity of unpolarised light be I₀. so the intensity of first polaroid   is  $\frac{I_{0}}{2}$. On rotating  through 60° , the intensity of light from second polaroid

$I=\frac{I_{0}}{2}(\cos 60)^{2}=\frac{I_{0}}{2}\frac{I}{4}=\frac{I_{0}}{8}=0.125 I_{0}$

 $\therefore$ percentage of incident light transmitted through the system=12.5%

• Physics - General questions