MHT CET 2020 :: Physics :: General questions

• Physics - General questions

 In the system of two particles of masses m₁ and m₂, the first particle is moved by a distance d towards the centre of mass.To keep the centre of mass unchanged, the second  particle will have  to be moved by a distance

Answer:

Explanation:

 Lert x₁  and x₂  be the position of masses m₁  and m₂, respectively 

 The position of centre of mass is 

$X_{CM}$=$\frac{x_{1}m_{1}+x_{2}m_{2}}{m_{1}+m_{2}}$

 If  $\triangle x_{1}$ and $\triangle x_{2}$  be the changes in positions , then change in the position  of the  centre of mass,

$\triangle X_{CM}=\frac{\triangle x_{1}m_{1}+\triangle x_{2}m_{2}}{m_{1}+m_{2}}$

 Given that  , the centre of mass remains unchannged  i.e, $\triangle$X_CM =0 and  $\triangle x_{1}$ =d

 $\Rightarrow 0=\frac{dm_{1}+m_{2}\triangle x_{2}}{m_{1}+m_{2}}$

 or    $\triangle x_{2}=-\frac{m_{1}}{m_{2}} d$

 In conversion of moving coil  galvanometer into an ammeter of required range, the resistance of ammeter , so formed is       

[ S= shunt and G= resistance of galvanometer]

Answer:

Explanation:

 A moving coil galvanometer can be converted into an ammeter by connecting a low resistance (called shunt resistance) in parallel to it.

 Hence, the resistance  (R) of the ammeter , so formed is 

$\frac{1}{R}=\frac{1}{S}+\frac{1}{G}$

$R=\frac{SG}{S+G}$

Five capacitors each of capacity C are connected as shown in the figure. If their resultant  capacity is 2 $\mu$ F, then the capacity  of each  condenser is 

Answer:

Explanation:

 Given, resultant capacity , C_eq  = 2 $\mu$ F

 The equivalent  capacity  of the circuit  is given by 

$\frac{1}{C_{eq}}=\frac{1}{C}+\frac{1}{C}+\frac{1}{C}+\frac{1}{C}+\frac{1}{C}$

                                    ($\because$  all capacitors are in series)

$\frac{1}{C_{eq}}=\frac{5}{C}$

$\frac{1}{2\mu F}=\frac{5}{C}$

 $\Rightarrow$      $ C=10\mu F$

 A absolute  zero temperature, pure silicon behaves as

Answer:

Explanation:

 The pure silicon has a negative temperature coefficient of resistivity

 At absolute zero temperature, its resistance becomes infinite and acts as an insulator.

A spherical rubber balloon carries a charge, uniformly distributed over the surface. As the balloon is blown up and increase in size. The total electric flux coming out of the surface

Answer:

Explanation:

 The electric field intensity  due to the point charge q placed at the centre of a sphere of radius r,

 $E=\frac{1}{4\pi \epsilon_{0}}\frac{q}{r^{2}}$

As the balloon is blown up, the charge enclosed by the Gaussian surface remains the same. So, electric field intensity remains the same. The electric flux is given by

$\phi= E.dS$

$\Rightarrow$    $ \phi\propto E$

 As E remains the same, the flux remains unchanged

• Physics - General questions