26.The combination of gates shown below yields A) OR gate B) NOT gate C) NAND gate D) XOR gate View Answer Report DiscussAnswer: Option AExplanation:The final boolean expression is $X=\left(\overline{\bar{A}.\bar{B}}\right)=\overline{\bar{A}}+\overline{\bar{B}} = A+B\Rightarrow OR gate$
27.An alternating voltage of 220 V 50 Hz frequency is applied across a capacitor of capacitance 2 μF. The impedence of the circuit is A) $\frac{\pi}{5000}$ B) $\frac{1000}{\pi}$ C) $500\pi$ D) $\frac{5000}{\pi}$ View Answer Report DiscussAnswer: Option DExplanation:Impedance of a capacitor is $X_{c} = \frac{1}{\omega c}$ $X_{c} = \frac{1}{2\pi fc}$ = $\frac{1}{2\pi\times50\times2\times10^{-6}} = \frac{5000}{\pi}$
28.The current in a coil of L = 40 mH is to be increased uniformly from 1 A to 11 A in 4 milli sec. The induced e.m.f will be A) 100 V B) 0.4 V C) 440 V D) 40 V View Answer Report DiscussAnswer: Option AExplanation:$e = \frac{LdI}{dt} = \frac{40\times10^{-3}(11-1)}{4\times10^{-3}} = 100 V$
29.Kerosene oil rises up in a wick of a lantern because of A) diffusion of the oil through the wick B) Capillary action C) buoyant force of air D) the gravitational pull of the wick View Answer Report DiscussAnswer: Option BExplanation:Kerosene oil rises up in wick of a lantern because of capillary action. If the surface tension of oil is zero, then it will not rise, so oil rises up in a wick of a lantern due to surface tension.
30.A smooth sphere of mass M moving with velocity u directly collides elastically with another sphere of mass m at rest. After the collision, their final velocities are V and v respectively. The value of v is A) $\frac{2uM}{m}$ B) $\frac{2um}{M}$ C) $\frac{2u}{1+m/M}$ D) $\frac{2u}{1+ M/m}$ View Answer Report DiscussAnswer: Option CExplanation:By law of conservation of momentum, Mu = MV +mv ...(1) Also e = $\frac{|v_{1}-v_{2}|}{|u_{1}-u_{2}|}\Rightarrow Mu = Mv-MV$ ....(2) From (1) and (2), 2Mu = (M+m)v $\Rightarrow v = \frac{2uM}{M+m}$ v = $\frac{2u}{1+m/M}$
