Transistor

Q. In a NPN transistor, 108 electrons enter the emitter in ${10}^{-8}\text{sec.}$ If $1\%$ electrons are lost in the base, the fraction of current that enters the collector and current amplification factor are respectively

1. $0.8\text{and}49$
2. $0.9\text{and}90$
3. $0.7\text{and}50$
4. $0.99\text{and}99$

Q.

State two causes of energy loss in a transformer.

Q.

Relate electric power in terms of potential difference and resistance.

Q. In common base mode of transistor, the collector current is 5.488 mA for an emitter current of 5.60 mA. The value of the base current amplification factor $\left(\beta \right)$ will be

1. 48
2. 49
3. 50
4. 51

Q.

A heater coil is connected to $220\mathrm{V}$ power supply , has a resistor of $150\mathrm{\Omega }$ . How long this coil takes to heat 1 kg of water from $20\mathrm{to}60°C$, assuming that all heat is taken up by water ?

(Given Heat capacity of water$=4186\mathrm{J}/\mathrm{kg}°\mathrm{C}$)

Q.

A metallic coil connected to a $220\text{V}$ supply, has a resistance of $110\Omega$ (while hot). How long will this coil take to heat $1\text{kg}$ of water from $20$ to ${70}^{\circ }C$? Assume that whole of heat produced by the coil is taken up by water.

(Heat capacity Of Water $=4186{\text{J/kg}}^{\circ }\text{C}$)

Q. $A$ time varying current $i$ is passed through a resistance $R$ as shown in figure. The total heat generated in the resistance is

1. $13(i_0{)}^{2}T{t}_0$
2. $11(i_0{)}^{2}T{t}_0$
3. $15(i_0{)}^{2}T{t}_0$
4. $17(i_0{)}^{2}T{t}_0$

Q. A heating element using nichrome connected to a $230V$ supply draws an intial current of $3.2A$ which settles after a few seconds to a steady value of $2.8A.$ What is the steady temperature of the heating element if the room temperature is ${27.0}^{\circ }C?$ Temperature coefficient of resistance of nichrome averaged over the tempature range involved is $1.70\times {10}^{-4}$ ${}^{\circ }{C}^{-1}$

Q.

A $4kW$ heater is connected to a $220V$source of power. Calculate

i. the electric current passing through the heater

Q. In a transistor circuit, the base current changes from $30\mu \text{A}\text{to}90\mu \text{A}$. If the current gain of the transistor is $30$, the change in the collector current is

1. $4\text{mA}$
2. $2\text{mA}$
3. $3.6\text{mA}$
4. $1.8\text{mA}$

Q. A resistor $R_1$ dissipates the power $P$ when connected to a certain generator. If the resistor $R_2$ is put in series with $R_1$, the power dissipated by $R_1$

1. decreases
2. remains the same
3. any of the above depending upon
   the relative values of $R_1$ and $R_2$
4. incareases

Q.

What is the formula for electrical power in terms of current (I) and resistance (R) of the resistor?

Q.

Show that electric power is given by $\frac{V^2}{R}$. What is the SI unit of electric power?

Q.

A metallic coil is connected to a $220\mathrm{V}$supply, has a resistance of $110\mathrm{\Omega }$ (while hot). How long will this coil take to heat 1kg of water from $20\mathrm{to}70°\mathrm{C}$? Assume whole of the heat produced by the is taken up by water.

(given: Heat capacity of water= $4186\mathrm{J}/\mathrm{kg}°\mathrm{C}$)

Q.

Electric power in terms of $V$ and $R$ is

1. $V^2/R$

2. $V/R^2$

3. $R^2/V$

4. $R/V^2$

Q.

Write formula for electric power in terms of current and resistance R.

Q. Current in a coil decreases down to zero from $l_0$ uniformly during a time interval $t_0$ If amount of heat generated in time $t=0tot=\frac{t_0}{2}is{H}_1$ and heat generated in the $t=\frac{t_0}{2}$ to $t=t_{0}is{H}_{2}then\frac{H_1}{H_2}is$

1. $3:1$
2. $5:1$
3. $1:1$
4. $7:1$

Q. The output characteristics of a transistor is shown in the figure. When $V_{CE}$ is $10\text{V},$ and $I_C=4.0\text{mA},$ then value of ${\beta }_{ac}$ is ________.

Q. In common base mode of transistor, the collector current is 5.488 mA for an emitter current of 5.60 mA. The value of the base current amplification factor $\left(\beta \right)$ will be

1. 48
2. 49
3. 50
4. 51

Q. Draw the typical input and output characteristics of an n-p-n transistor in CE configuration. Show how these characteristics can be used to determine (a) the input resistance $\left(r_i\right)$, and (b) current amplification factor $\beta$.

Input charcteristics: It is the graph drawn between input current and input voltage when output voltage is kept constant.

Output characteristics : It is the graph drawn between output current and output voltage when input current is kept constant.

(a) Input resitance $(R_i$

$={\left[\frac{\text{Change in emitter base voltage}(△V_{BE})}{\text{Change in base current}(△I_B)}\right]}_{\text{at constant}{V}_{CE}}$


or $R_i={\left(\frac{△V_{BE}}{△I_B}\right)}_{V_{CE}}$

(b) Current amplification factor, $\left(\beta \right)={\left(\frac{△I_C}{△I_B}\right)}_{V_{CE}}$

= $\frac{△I_C}{△I_E-△I_C}$

= $\frac{\frac{△I_C}{△I_E}}{\frac{△I_C}{△I_E}-\frac{△I_C}{△I_E}}$

= $\frac{\alpha }{1-\alpha }$

$\Rightarrow \beta =\frac{\alpha }{1-\alpha }$

Q. In a silicoo transistor, base current is charged by $20{\mu }_A$. This results is a charge of 0.02 V in base emitter voltage and a change of $2mA$ in the collection current.
(a) Find the input resistance Base and trans-conductance of the transistor.
(b) The transistor is used as an amplifier with the load resistance 5 kz. What is the voltage gain of the amplifier?

Q. In a common emitter (CE) amplifier having a voltage gain $G$, the transistor used has transconductance $0.03mho$ and current gain $25$. If the above transistor is replaced with another one with transconductance $0.02mho$ and current gain $20$, the voltage gain will be

1. $\frac{2}{3}G$
2. $1.5G$
3. $\frac{5}{4}G$
4. $\frac{1}{3}G$

Q.

Write the expression for electric power, when

1. Voltage and current given
2. Current and resistance given
3. Voltage and resistance given

Q. The current gain $\alpha$ of a transistor is defined as

1. the ratio of change in collector current to the change in emitter current for a constant value of collector voltage in a common base arrangement.
2. the ratio of change in collector current to the change in base current for a constant collector voltage in a common collector arrangement.
3. the ratio of change in collector current to the change in base current for constant collector voltage in a common emitter arrangement.
4. the ratio of change in emitter current to the change in collector current for a constant emitter voltage in a common emitter arrangement

Q. In a common base transistor circuit, the current gain is $0.98$. On changing the emitter current by $5.00$mS, the change in collector current is$?$

1. $0.196$mA
2. $2.45$mA
3. $4.9$mA
4. $5.1$mA

Q. In a common-base mode of a transistor, the collector current is $5.488\text{mA}$ for an emitter current of $5.60\text{mA}$. The value of the current amplification factor $\left(\beta \right)$ will be

1. $49$
2. $50$
3. $51$
4. $48$

Q.

An electric heater of power $1470W$ has a resistance of $30\Omega$. Calculate the magnitude of

1. the current
2. the p.d. at its end.

Q. Explain using circuit diagram the working of n-p-n transistor as CE amplifier. Hence obtain expression for its voltage gain in common emitter configuration.

Q. Assertion :If the forward current changed by $1.5$ mA when the forward voltage in semiconductor triode is changed from $0.5V$ to $2V$, the forward resistance of diode will be $1\Omega$. Reason: The forward resistance is given by $R_f=\frac{\Delta V_f}{\Delta I_f}$

1. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
2. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
3. Assertion is incorrect but Reason is correct
4. Both Assertion and Reason are incorrect

Q. In the circuit shown, the current in the 1$\Omega$ resistor is :

1. 1.3 A, from P to Q
2. 0 A
3. 0.13 A, from Q to P
4. 0.13 A, from P to Q