Introduction to Transistor

Q. The tension in a wire is decreased by 19% the percentage decrease in frequency will be

Q.

Can a transistor amplify DC?

Q. How to find whether springs are connected in series or parallel?

Q. The most commonly used transistor arrangement is .

1. common emitter
2. common base
3. common collector

Q. An annular disc has inner and outer radius $R_1$​ and $R_2$​ respectively. Charge is uniformly distributed. Surface charge density is $\sigma$. Find the electric field at any point distant $y$ along the axis of the disc.

1. $\frac{\sigma }{2{ϵ}_0}$
2. $\frac{\sigma y}{2{ϵ}_0}[\frac{1}{\sqrt{R_1^2+y^2}}-\frac{1}{\sqrt{R_2^2+y^2}}]$
3. $\frac{\sigma }{2{ϵ}_0}\log \frac{R_2+y}{R_1+y}$
4. $\frac{\sigma y}{2{ϵ}_0(R_2-R_1)}$

Q. A point charge $-q$ having mass $m$ is placed at the centre of a uniformly charged ring of charge $Q$ and radius $R$. Find the time period of oscillation if the point charge is slightly displaced and released.

1. $T=2\pi \sqrt{\frac{m{R}^3}{KQq}}$
2. $T=2\pi \sqrt{\frac{m{R}^2}{KQq}}$
3. $T=2\pi \sqrt{\frac{m{R}^3}{2KQq}}$
4. None of the above

Q. In which of the following situations, the transistor is operating in the active region ?

1. 
2. 
3. 
4. 

Q.

In a common emitter transistor, the current gain is 80. What is the change in collector current, when the change in base current is 250 mA

1. 80 ´ 250 mA

2. (250 - 80) mA
3. (250 + 80) mA
4. 250/80 mA

Q. A uniform electric field $E$ is created between two parallel and oppositely charged plates as shown in figure. An electron enters the field symmetrically between the plates with a speed $v_0$. The length of each plate is $l$. Find the angle of deviation (which is given by $\theta$ in the figure) of the path of the electron as it comes out of the field interms of mass of electron $m$ and charge of the electron $e$. (Acceleration due to gravity can be neglected)

1. $\theta ={\tan }^{-1}\left(\frac{eEl}{m{v}_0^2}\right)$
2. $\theta ={\cot }^{-1}\left(\frac{2eEl}{m{v}_0^2}\right)$
3. $\theta ={\tan }^{-1}\left(\frac{2eEl}{m{v}_0^2}\right)$
4. $\theta ={\tan }^{-1}\left(\frac{eE}{m{v}_0^2}\right)$

Q. Two point charges of $3.2\times {10}^{-19}\text{C}$ and $-3.2\times {10}^{-19}\text{C}$ are seperated from each other by $2.4\times {10}^{-10}\text{m}$. The dipole is situated in a uniform electric field of intensity $4\times {10}^5\text{V/m}$. The work done in rotating the dipole by ${180}^{\circ }$ is $p\times {10}^{-24}\text{J}$. Find the value of $p$.