{"id":88511,"date":"2021-06-24T16:55:35","date_gmt":"2021-06-24T11:25:35","guid":{"rendered":"https:\/\/kseebsolutions.guru\/?p=88511"},"modified":"2021-07-01T12:34:59","modified_gmt":"2021-07-01T07:04:59","slug":"1st-puc-electronics-question-bank-chapter-7","status":"publish","type":"post","link":"https:\/\/kseebsolutions.guru\/1st-puc-electronics-question-bank-chapter-7\/","title":{"rendered":"1st PUC Electronics Question Bank Chapter 7 Bipolar Junction Transistor"},"content":{"rendered":"
One Mark Questions and Answers<\/span><\/p>\n Question 1. <\/p>\n Question 2. Question 3. Question 4. (ii) pnp transistor <\/p>\n Question 5. Question 6. Question 7. <\/p>\n Question 8. Question 9. Question 10. Question 11. Question 12. Question 13. Question 14. <\/p>\n Question 15. Question 16. Question 17. Question 18. Question 19. <\/p>\n Two Mark Questions and Answers<\/span><\/p>\n Question 1. Question 2. Question 3. The region of output characteristics between VCE<\/sub> = O and knee voltage is called saturation region. In this region, both emitter base and collector base junctions are forward biased.<\/p>\n <\/p>\n Question 4. Question 5. Question 6. Question 7. Question 8. <\/p>\n Question 9. Question 10. Question 11. Five Mark Questions and Answers<\/span><\/p>\n Question 1. The negative terminal of VE<\/sub>E<\/sub> repels the majority charge carriers electrons in the n type emitter towards the base region. When VE<\/sub>E<\/sub> is greater than the barrier potential of emitter base junction the electrons from emitter region move to thep type base region. This forms the emitter current L.<\/p>\n The base is thin and has only few electrons. Hence only few electrons and holes recombine and this forms the base current IE<\/sub>. The remaining free electrons in the base region move to collector region attracted by the +VCC<\/sub>. They move through the collector region into +VCC<\/sub>, This forms the collector current IC<\/sub>.<\/p>\n The relation connecting the currents in the transistor is IE<\/sub> = IB<\/sub> + IC<\/sub><\/p>\n <\/p>\n Question 2. 2. Common emitter configuration: 3. Common collector Configuration: Question 3. The two types of characteristics are :<\/p>\n Input Characteristics: <\/p>\n Input resistance Rm<\/sub> = \\(\\frac{\\Delta \\mathrm{V}_{\\mathrm{BE}}}{\\Delta \\mathrm{I}_{\\mathrm{B}}}\\)<\/p>\n <\/p>\n CE output characteristics Question 5. Active Region: Active region is the region of the output characteristics to the right of knee voltage and above IB<\/sub> = O. The emitter base junction is forward biased and the collector base junction is reverse biased. In amplifiers, the transistor is operated in the active region.<\/p>\n <\/p>\n
\nWhat is a transistor?
\nAnswer:
\nThe transistor is a three-terminal semiconductor device with two p-n junctions which can amplify weak electrical signals and it can also be used as a switch.<\/p>\n
\nWrite one important application of a transistor.
\nAnswer:
\nAmplification of weak ac signal.<\/p>\n
\nWhat is an npn transistor?
\nAnswer:
\nnpn transistor is a semiconductor device that has a layer of p type material sandwiched between two layers of n-type materials.<\/p>\n
\nDraw the symbols of (i) npn transistor and (ii) pnp transistor
\nAnswer:
\n(i) npn transistor
\n<\/p>\n
\n<\/p>\n
\nWhy is a transistor called a transfer resistor device?
\nAnswer:
\nA transistor is called a transfer resistor device because it transfers charge carriers from a low resistance region to a high resistance region.<\/p>\n
\nHow many p-n junctions a transistor has?
\nAnswer:
\nTwo<\/p>\n
\nWhat is an unbiased transistor?
\nAnswer:
\nA transistor without an external voltage (or biasing) applied is called an unbiased transistor.<\/p>\n
\nWhat is a biased transistor?
\nAnswer:
\nA transistor with an external voltage applied is called a biased transistor.<\/p>\n
\nMention (i) heavily doped region (ii) lightly doped regions of a transistor.
\nAnswer:<\/p>\n\n
\nWrite the relation between the current components of a transistor.
\nAnswer:
\nIE<\/sub> = IB<\/sub> + IC<\/sub><\/p>\n
\nWhat does the arrow in the circuit symbol of transistor indicate?
\nAnswer:
\nThe arrow is the symbol of the transistor indicates the direction of flow of conventional current.<\/p>\n
\nIn which mode of operation the transistor can be used as an amplifier?
\nAnswer:
\nActive mode.<\/p>\n
\nIn which modes of operation the transistor can be used as a switch?
\nAnswer:
\nSaturation (closed switch) and cutoff (open switch)<\/p>\n
\nWhat is an optocoupler?
\nAnswer:
\nIt is a device that connects two electrical circuits by means of an optical interface.<\/p>\n
\nWrite the regions of the transistor in the decreasing size of their area.
\nAnswer:
\nCollector, emitter, base.<\/p>\n
\nMention the regions of the transistor in the increasing doping levels.
\nAnswer:
\nBase, collector, emitter.<\/p>\n
\nWhich are the (i) largest and (ii) smallest currents of a transistor?
\nAnswer:<\/p>\n\n
\nHow are emitter-base and collector-base junctions biased in forwarding active mode?
\nAnswer:
\nEmitter base junction is forward biased and collector-base junction is reverse biased.<\/p>\n
\nWhy npn transistors are often used?
\nAnswer:
\nThe majority of charge carriers in npn transistors are free electrons which have more mobility compared to the holes. Hence npn transistors are often used.<\/p>\n
\nWhy is the collector of a transistor made larger?
\nAnswer:
\nThe collector of a transistor is made larger to dissipate the heat produced due to the flow of current.<\/p>\n
\nDistinguish between \u03b1dc and \u03b2dc.
\nAnswer:
\n\u03b2dc<\/sub> is the DC current gain which is the ratio collector current to emitter current in CB mode. \u03b2dc<\/sub> is the decurrent gain in CE mode which is the ratio of collection current to base current.
\n\u03b1dc<\/sub> = \\(\\frac{\\mathrm{I}_{\\mathrm{C}}}{\\mathrm{I}_{\\mathrm{E}}}\\) and \u03b2dc<\/sub> = \\(\\frac{\\mathrm{I}_{\\mathrm{C}}}{\\mathrm{I}_{\\mathrm{B}}}\\)<\/p>\n
\nDistinguish between cutoff region and saturation region.
\nAnswer:
\nThe region of the output characteristics below IB<\/sub> = OA is known as cutoff region . In cut off region, both emitter base and collector base junctions are reverse biased.<\/p>\n
\nWhat is a phototransistor? Draw its symbol.
\nAnswer:
\nA photo transistor is a three terminal optoelectronics device.
\n<\/p>\n
\nWrite any two application of phototransistors.
\nAnswer:<\/p>\n\n
\nMention lightly doped and moderately doped regions of a transistor.
\nAnswer:
\nLighty doped region of transistor is base and moderately doped region is collector.<\/p>\n
\nWhat is an IR transistor?
\nAnswer:
\nIR transistor is a phototransistor which is sensitive to the infrared radiation.<\/p>\n
\nWrite any two applications of an IR transistor.
\nAnswer:
\nIR transistors are used in<\/p>\n\n
\nWhich is the smallest of all the three currents in a transistor?
\nAnswer:
\nBase current (IB<\/sub>).<\/p>\n
\nHow are emitter base junction and collector base junctions biased under normal operation?
\nAnswer:
\nEmitter base junction is forward biased and collector base junction is reverse biased.<\/p>\n
\nWhat are saturation and cutoff regions?
\nAnswer:
\nSaturation region is the region of output characteristics between VCE<\/sub> = O and knee voltage. Cut off region is the region of the output characteristics below IB<\/sub> = O.<\/p>\n
\nExplain the working of an npn transistor.
\n
\nAnswer:
\nThe emitter base junction is forward biased by power supply VEE<\/sub>\u00a0and the collector base junction is reverse biased by the power supply VCC<\/sub>.<\/p>\n
\nExplain the different types of transistor configurations.
\nAnswer:
\nThe different types of transistor configurations are.
\n1. Common base configuration:
\nIn this mode, base terminal is made common to both the input and output circuits. The input is applied between emitter and base terminals and the output is taken across collector and base terminals. CB configuration is used in high frequency amplifiers.
\n
\nThe current gain in CB mode is \u03b1 = \\(\\frac{\\text { output current }}{\\text { input current }}\\)
\n\u03b1 = \\(\\frac{\\mathrm{I}_{\\mathrm{C}}}{\\mathrm{I}_{\\mathrm{E}}}\\)<\/p>\n
\nIn this mode, emitter is made common to both input and output circuits. The input is applied between base and emitter terminals and the output is taken between collector and emitter terminals. CE configuration of the transistor is used in amplifier circuits.
\n
\nCurrent gain in CE configuration is \u03b2 = \\(\\frac{\\mathrm{I}_{\\mathrm{C}}}{\\mathrm{I}_{\\mathrm{E}}}\\)<\/p>\n
\nIn this mode, collector is mode common to both the input and output circuits. The input is applied between base and colleqtor terminals and the output is taken from emitter and collector terminals.<\/p>\n
\nCC configuration is used buffer amplifier and for impedance matching circuits.<\/p>\n
\nExplain CE mode input and output characteristics of a npn transistor. Distinguish between the cutoff, active and saturation regions of a transistor.
\nAnswer:
\n
\nThe circuit to plot the CE characteristics of the transistor is as shown in the diagram.<\/p>\n\n
\nIt gives the relationship between input voltage VBE and the input current IB, when the output voltage VCE<\/sub> is kept constant. VBE<\/sub> is varied and corresponding IB values are noted keeping VCE<\/sub> constant. The input characteristics curve is similar to that of a forward biased semiconductor diode as emitter base junctioni s a pn junction.<\/p>\n
\nIt is a graph of output collector current Ic against output collector to emitter voltage VCE<\/sub> for a constant input base current IB<\/sub>.
\n
\nFrom the graph, it is clear that the output current Ic depends upon input current IB<\/sub> and VCE<\/sub> has no control over IC<\/sub>.
\nOutput resistance, Rout<\/sub>\u00a0= \\(\\frac{\\Delta V_{\\mathrm{CE}}}{\\Delta \\mathrm{I}_{\\mathrm{C}}}\\)<\/p>\n
\nDraw the output characteristics of a transistor in CE configuration. Show different regions of operation. What are biasing requirements for the transistor to operate in these regions..
\nAnswer:
\n
\nSaturation Region: The region of output characteristics between VCE<\/sub> = O and knee voltage VK<\/sub> is called saturation region. Both emitter base and collector base junctions are forward biased in this region . With the increase in VCE<\/sub>, collection current Ic increases.<\/p>\n