26.A metallic bar is heated from 0° C to 100° C. The coefficient of linear expansion is $10^{-5}K^{-1}$. What will be the percentage increase in length A) 0.01% B) 0.1% C) 1% D) 10% View Answer Report DiscussAnswer: Option BExplanation:$\frac{\triangle l}{l}=\alpha \triangle T=10^{-5}\times 100=10^{-3}$ $\frac{\triangle l}{l}\times 100$ % $=10^{-3}\times 100=10^{-1}=0.1$ %
27. A (+ve) vely charged particle is placed in an infinitely long straight conductor where there is zero gravity. then A) the charged particle will not move B) it will move parallel to the straight conductor C) it will move perpendicular to the straight conductor D) it will move constant acceleration View Answer Report DiscussAnswer: Option AExplanation:As the changed particle is at rest , no force will act on it due to the magnetic field produced by the conductor at the site of the charge . Hence, it will remain at rest.
28.Which statement is correct for the given circuit ? A) I through $R_{1} > 1 $ through $ R_{2}$ B) I through $R_{3} > 1 $ through $R_{2}$ and $R_{1}$ C) I through $R_{2} > 1 $ through $R_{3}$ and $R_{1}$ D) I is same in $R_{1}$ , $R_{2}$ , $R_{3}$ View Answer Report DiscussAnswer: Option DExplanation: $R_{1}$ , $R_{2}$ and $R_{3}$ are in series. Therefore , same current will flow through all the resistors
29.Two solenoids are given- 1st has 1 turn per unit length and 2nd has n turns per unit length.Ratio of magnetic fields at their centres is A) n:1 B) 1:n C) $1:n^{2}$ D) $n^{2}:1$ View Answer Report DiscussAnswer: Option BExplanation: Magnetic field $\propto$ no. of turns per unit length $\therefore$ Required ratio =1:n
30. The wavelength of an electron for the transition from a state n1 to n2 is $\frac{9}{8R}$ which of the following wavelength is possible for a transition from n2 to n1 A) $\frac{16}{15R}$ B) $\frac{4}{3R}$ C) $\frac{9}{8R}$ D) $\frac{36}{5R}$ View Answer Report DiscussAnswer: Option CExplanation:Energy released in transition from state n1 to n2 is equal to the energy absorbed in transition from state n2 to n1
