MHT CET 2018 :: Physics :: General questions

• Physics - General questions

An ideal transformer converts 200 V  AC to 3.3 kV  AC to transmit a power of 4.4 kW .If primary coil has 600 turns, then alternating current in the secondary coil is 

Answer:

Explanation:

 Given, input voltage (V_p) =220 V

 Output voltage (V_s) = 3.3 x 10³ V

 Power (P) = 4.4 kW = 4.4 x 10³ W

 Number of turns in primary coil = 600

 We know that,

   $P= V_{p}\times I_{p} \Rightarrow I_{p}=\frac{P}{V_{p}} or I_{p}=\frac{4.4\times 10^{3}}{220}=20A$

 For an ideal transformer,

$\frac{V_{s}}{V_{p}}=\frac{I_{p}}{I_{s}}$

$I_{s}=I_{p}\times\frac{V_{p}}{V_{s}}$

$I_{s}=\frac{20\times220}{3.3 \times 10^{3}}$

 or  $I_{s}=\frac{44}{33}=\frac{4}{3}A$

A metal wire of density $\rho$  floats on a water surface horizontally. If it is NOT to  sink in water , then maximum radius  of wire is proportional to (where, T= surface tension of water, g= gravitational  acceleration)

Answer:

Explanation:

Given, density of metal wire = $\rho$

 The surface tension of water = T

 If l is the length of the wire and f the total force on either side of the wire, then

 f= Tl ......(i)

 Also, f= mg  .......(ii)

 From, Eqs. (i) and (ii), we get

Tl= mg

 Tl= v$\rho$ g          [ $\because Density (\rho)=\frac{m}{v}$]

  $Tl= \pi r^{2}l\rho g$

$r^{2}=\frac{T}{\pi \rho g}\Rightarrow r=\sqrt{\frac{T}{\pi \rho g}}$

If M_z = magnetisation  of a paramagnetic sample, B- external magnetic field, T= absolute temperature, C= curie constant, then  according to Curie's law in magnetism, the correct relation is 

Answer:

Explanation:

Here, 

 M₂= magnetization of a paramagnetic sample

B= external magnetic field

 T= absolute temperature

C= Curie constant

 Curie's law in magnetism states that in paramagnetic material, the material's magnetization is directly proportional to the applied field, but when temperature increases the relation is reversed, i.e, the magnetization becomes inversely proportional to the temperature. Mathematically, it is written as 

$M_{2}=\frac{C\times B}{T}\Rightarrow C= \frac{M_{2}.T}{B}$

If the numerical  aperture of a microscope is increased, then is 

Answer:

Explanation:

 Resolving limit of microscope   is given by

$RL=\frac{\lambda}{2\mu \sin\alpha}$

 where, $\mu$ sin $\alpha$ is called numerical aperture [NA]

 and $\lambda$ = wavelength of light

 $\therefore$   $RL=\frac{\lambda}{2(NA)}$

 Hence, if numerical aperture of a microscope is increased , then its limit of resolution is decreased.

The angle made by an incident ray of light with reflecting surface is called

Answer:

Explanation:

 The angle made by an incident ray of light with a reflecting surface is called a glancing angle.

• Physics - General questions