Tag: physics

Questions Related to physics

For a CE transistor amplifier, the audio signal voltage across the collector resistance of $2k\Omega $ is 2 V.Suppose the current amplification factor of the transistor is 100. The value of ${R _B}$ in series with ${V _{BB}}$ the supply of 2V, if the DC base current has to be 10 times the signal current is 

  1. $4k\Omega $

  2. $14k\Omega $

  3. $28k\Omega $

  4. $54k\Omega $


Correct Option: C

When a collector to emitter voltage is constant in a transistor, the collector current changes by $8.2mA$ when the emitter current changes by $8.3mA$. The value of forward current ratio $B$ is

  1. $82$

  2. $83$

  3. $8.2$

  4. $8.3$


Correct Option: A

In the CB mode of a transistor when the collector voltage is changed by $0.5V$. The collector current changes by $0.05mA$. The output resistance will be

  1. $10k\Omega$

  2. $20k\Omega$

  3. $5k\Omega$

  4. $2.5k\Omega$


Correct Option: A

Consider an n-p-n transistor amplifier in common-emitter configuration. The current gain of the transistor is $100$. if the collector current changes by $1mA$. What will be the change in emitter current.

  1. $1.1mA$

  2. $1.01mA$

  3. $0.01mA$

  4. $10mA$


Correct Option: B

Power gain for $N - P - N$ transistor is $10^6$, input resistance $100 \Omega$ and output resistance $1000 \,\Omega$. find out current gain.

  1. $100$

  2. $150$

  3. $200$

  4. $50$


Correct Option: A
Explanation:

Power gain = $(Current \, gain)^2 \left(\dfrac{R _{out}}{R _{in}} \right)$
$10^6 = \beta^2 \times \dfrac{10^4}{100}$
$\beta = 100$

A transistor, when connected in common emitter mode, has a:

  1. high input resistance and a low output resistance

  2. medium input resistance and high output resistance

  3. very low input resistance and a low output resistance

  4. high input resistance and a high output resistance


Correct Option: C

What is the voltage gain in a common emitter amplifier, where input resistance is $3.2$ and load resistance $24$$\Omega, \beta$$ = 0.6$?

  1. $8.4$

  2. $4.8$

  3. $2.4$

  4. $480$


Correct Option: B
Explanation:

Voltage gain, $\displaystyle A _v = \beta \dfrac{R _L}{R _i} = 0.6 \times \dfrac{24}{3} = 4.8$

In a common emitter transistor amplifier $\beta$ $= 60$, $R _0$ $= 5000$$\Omega$ and internal resistance of a transistor is $500$$\Omega$. The voltage amplification of amplifier will be

  1. $500$

  2. $460$

  3. $600$

  4. $560$


Correct Option: C
Explanation:

Voltage amplification, $\displaystyle A _v = \beta \dfrac{R _0}{R _i} = 60 \times \dfrac{5000}{500} = 600$

In a triode, $g$$ _m$ $= 2$ $\times$$ 10$$^{-3}$ $\Omega^{-1}$, $\mu$ $= 42$, resistance of load, $R = 50k\Omega$. The voltage amplification obtained from this triode will be

  1. $30.42$

  2. $29.57$

  3. $28.18$

  4. $27.15$


Correct Option: B
Explanation:

Voltage gain, $\displaystyle A _v = \beta \dfrac{R _L}{R _i} = 0.6 \times \dfrac{24}{3} = 4.8$

The grid voltage of any triode valve is changed from -1 volt to -3 volt and the mutual conductance is 3$\times$ 10$^{-4}$ mho. The change in plate circuit current will be

  1. 0.8 mA

  2. 0.6 mA

  3. 0.4 mA

  4. 1 mA


Correct Option: B
Explanation:

$\displaystyle g _m = \frac{\Delta I _p}{\Delta V _g}$

or $\Delta I _p = g _m \times \Delta V _g = 3 \times 10^{-4} \times [-3-(-1)]$
$= - 0.6 \times 10^{-3} A$ = shortage of $0.6 \times 10^{-3}A$