JEE 2017 :: Main 2017 :: Physics 2017

• Main 2017 - Physics 2017
• Main 2017 - Chemistry 2017
• Main 2017 - Mathematics 2017

In the beow circuit , the current in each resistance is

Answer:

Explanation:

Each resistance is converted with two cells combined in opposite direction. so, potential drop across each resistor is zero. Hence the current through each of resistor is zero.

In the given circuit diagram, when the current reaches a steady state in the circuit, the charge on the capacitor of capacitance C  will be

Answer:

Explanation:

In steady-state , no current flow through the capacitor, So, resistance becomes ineffective.

   So, the current in circuit

   $      I= \frac{E}{r+r_{2}(Total Resistance)}$

$\because$   Potential drop  across capacitor

                             = Potential drop across r₂ =I r₂ = $\frac{Er_{2}}{r+r_{2}}$

  $\therefore$       Stored charge of capacitor . Q= CV

                               = $CE \frac{r_{2}}{(r_{}+r_{2})}$

A capacitance of 2µF is required in an electrical circuit across a potential difference of 1kV. A large number of 1 µ F  capacitors are available which can withstand a potential difference of not more than 300 V. The  minimum number of capacitors required to achieve this is

Answer:

Explanation:

As a each capacitor cannot withstand more than 300V, so there should be four capacitors in each row became in the condition 1kV   i.e, 1000V will be divided by 4 (i.e. 250 not more than 300V)

    Now,equivalent capacitance of one row

                                         = $\frac{1}{4}\times 1\mu F=0.25\mu F$

                         [ $\therefore $ in series combination , $C_{eq}=\frac{c}{n}$ ]

Now, we need equivalent of 2μ F, so let

                we need n such rows

                                      $\therefore $    n × 0.25=2μF

                           [ $\therefore $  in parallel combination C_eq =nc]

                       $n=\frac{2}{0.25}$

                              =8

$\therefore $    Total number of capacitors = number of rows × number of capacitors in each row= 8 × 4=32

Which of the following statements is false?

Answer:

Explanation:

In a balanced Wheatstone bridge, there is no effect on the position of a null point. If we exchange the battery and the galvanometer. So, option (a) is incorrect

A radioactive nucleus A with a half-life T, decays into a nucleus B. At t=0, there is no nucleus B. After sometimes t. the ratio of the number of B to that of A is 0.3. Then, t is given by

Answer:

Explanation:

Decay scheme is,

Given        $\frac{N_{B}}{N_{A}}=0.3=\frac{3}{10}$

                 $\Rightarrow\frac{N_{B}}{N_{A}}=\frac{30}{100}$

  So,    N₀  =100+30=130 atoms

     By using  $N= N_{0}e^{-\lambda t}$

   We have , $100= 130e^{-\lambda t}$

           $\Rightarrow     \frac{1}{13}=e^{-\lambda t}\Rightarrow log1 .3=\lambda t$

    If T is half-life, then $t=\frac{\log_{e}{2}}{T}$

                 $\Rightarrow \log_{}{1.3}=\frac{\log_{e}{2}}{T}.t$

                               $\therefore     t=\frac{T.\log_{}{(1.3)}}{\log_{e}{2}}$

• Main 2017 - Physics 2017
• Main 2017 - Chemistry 2017
• Main 2017 - Mathematics 2017