Topic 4 of 5 โข Chapter: Electronics โข Physics
Transistors โ Complete Notes, Revision, Important Questions & Downloads
Transistors in Electronics is built around Bipolar Junction Transistors (BJT), Transistor Operating Modes, Transistor Configurations, Field-Effect Transistor (FET), Transistor as Amplifier, Transistor Gains and Parameters, Transistor as Oscillator. NEET tests Transistors by asking you to identify which of these exact subtopics controls the setup, then apply the correct relation, sign convention, or limiting condition. A standard trigger is I_e = I_b + I_c, so the safe route is to map the wording back to the exact subtopic before any substitution. This page stays inside the Class 12 NEET scope: it keeps the textbook definitions, adds the exam-useful trap checks, and avoids university-level extensions that are outside the assigned OCR pages.
7 SubtopicsTheoryHard Difficulty
Expected QuestionsQ
1-2
Transistors usually appears as a direct NEET tool: sometimes direct, often embedded inside a larger electronics calculation or concept check.
Time Requiredโฑ
2-2.5 hrs
One pass to lock the formula or definition of each subtopic, one pass to solve NEET-style stems that force you to choose between nearby relations from Transistors.
Difficultyโก
Hard
Transistors is hard because the arithmetic is rarely the real issue; the real filter is whether you recognize the exact condition behind the active subtopic quickly enough.
NRI USA Curriculum GapUS
Medium
AP Physics 2 and AP Physics C usually cover the broad physics idea, but NEET expects faster textbook-speed recognition of Transistors, especially the short trigger conditions attached to Bipolar Junction Transistors (BJT).
7Subtopics
7Practice Questions
4Free Downloads
2-2.5 hrsPrep Time
NEET Weightage โ Transistors
Electronics (Chapter 27)| NEET Year | Questions from this Topic | Bar | Marks |
|---|---|---|---|
| 2024 | 1 | 4 | |
| 2023 | 0 | 0 | |
| 2022 | 1 | 4 | |
| 2021 | 0 | 0 | |
| 2020 | 1 | 4 | |
| 2019 | 0 | 0 | |
| 6-Year Pattern (2019โ2024) | 1-2 | ย | 4-8 |
Transistors is usually unlocked by spotting the right subtopic first: Bipolar Junction Transistors (BJT) is rarely interchangeable with the rest of the chapter even when the symbols look familiar.
The chapter emphasis is operational rather than decorative: NEET asks you to use Transistors inside a live setup, not just repeat the definition of Transistor Operating Modes.
The most reliable mark-saving habit in Transistors is to check sign, medium, geometry, or device condition before simplifying the formula.
The chapter emphasis is operational rather than decorative: NEET asks you to use Transistors inside a live setup, not just repeat the definition of Transistor Operating Modes.
The most reliable mark-saving habit in Transistors is to check sign, medium, geometry, or device condition before simplifying the formula.
1-2
Avg Questions / Year
4-8
Total Marks (6 yrs)
Direct
Pattern
Hard
Difficulty
Exam Strategy for Transistors
1
Lock one usable relation for each Transistors subtopic Write the main relation or textbook sentence for Bipolar Junction Transistors (BJT), Transistor Operating Modes, Transistor Configurations, Field-Effect Transistor (FET). Attach one condition of validity to each so you know when the relation can actually be used in NEET.
2
Classify the stem before calculating Decide whether the problem is asking for magnitude, direction, image position, current, device action, carrier behavior, or communication mode. That classification tells you which part of Transistors is active.
3
Run one trap check before marking the answer For Transistors, the final mistake is usually not algebra; it is a missed sign convention, wrong medium, wrong branch of a device characteristic, or confusion between two nearby subtopics. Check that before you stop.
4
Revise Transistors with mixed stems, not isolated notes After revising the page once, solve short chapter-level questions that force you to distinguish Bipolar Junction Transistors (BJT) from the neighboring ideas. That is much closer to the way NEET actually uses this topic.
Download Study Notes โ Transistors
PDF ยท Cheat Sheet ยท MCQ Set ยท PYQTransistors โ Full Notes
Complete topic notes covering all 7 subtopics in Transistors, with the governing relation, the validity condition, and one worked example per subtopic.
Download PDFTransistors โ Formula Sheet
One-page formula sheet for Transistors: compact relations, sign conventions, and short reminders of where each formula is valid.
Download PDFTransistors โ MCQ Practice
7 application-driven MCQ practice questions built from the same setups, devices, or optical geometries that NEET uses in Transistors.
Download PDFTransistors โ PYQ Practice
NEET-style PYQ practice set for Transistors that highlights the shortest reliable route from the active subtopic to the correct answer.
Download PDFSubtopics in Transistors
2-Column TableRapid Revision โ Transistors
Concept โ Trap โ Example1) Bipolar Junction Transistors (BJT)
Definition + ApplicationElectronic device derived from 'transfer resistor'. No heater needed. Small and light. Current operated device. Consists of three regions: Emitter (E), Base (B), Collector (C).
- Use Bipolar Junction Transistors (BJT) only when the stem is explicitly controlled by that exact physical object, device block, optical geometry, or transmission mode.
- Before calculating in Bipolar Junction Transistors (BJT), check the validity condition mentioned in the page: sign convention, medium, current direction, carrier type, or image-formation rule.
- Trap in Bipolar Junction Transistors (BJT): device questions reward correct terminal or carrier identification; the common error is to mix the role of majority carriers, current direction, or gate truth condition.
Example (NEET-style)Example: a 100 W, 200 V bulb connected to 100 V draws 25 W because power scales as V^2 when the resistance of the filament is unchanged.
2) Transistor Operating Modes
Definition + ApplicationEmitter junction forward biased, collector junction reverse biased. Transistor acts as amplifier.
- Use Transistor Operating Modes only when the stem is explicitly controlled by that exact physical object, device block, optical geometry, or transmission mode.
- Before calculating in Transistor Operating Modes, check the validity condition mentioned in the page: sign convention, medium, current direction, carrier type, or image-formation rule.
- Trap in Transistor Operating Modes: device questions reward correct terminal or carrier identification; the common error is to mix the role of majority carriers, current direction, or gate truth condition.
Example (NEET-style)Example: if alpha = 0.98 for a transistor, beta = alpha/(1-alpha) = 49, so a 0.04 mA base current can control about 1.96 mA collector current in common-emitter mode.
3) Transistor Configurations
Formula + ApplicationBase common to input and output. Input current = I_e, input voltage = V_EB. Output voltage = V_CB, output current = I_c. Input resistance โ 100ฮฉ. Dynamic input resistance R_i = (ฮV_EB/ฮI_e) at V_CB constant.
- Use Transistor Configurations only when the stem is explicitly controlled by that exact physical object, device block, optical geometry, or transmission mode.
- Before calculating in Transistor Configurations, check the validity condition mentioned in the page: sign convention, medium, current direction, carrier type, or image-formation rule.
- Trap in Transistor Configurations: device questions reward correct terminal or carrier identification; the common error is to mix the role of majority carriers, current direction, or gate truth condition.
Example (NEET-style)Example: if alpha = 0.98 for a transistor, beta = alpha/(1-alpha) = 49, so a 0.04 mA base current can control about 1.96 mA collector current in common-emitter mode.
4) Field-Effect Transistor (FET)
Definition + ApplicationN-channel FET consists of N-type material block with P-type material strip (gate) on side. PN junction reverse biased. Gate voltage controls channel depletion and current. Extremely high input impedance. Unipolar device. Slower than junction transistor.
- Use Field-Effect Transistor (FET) only when the stem is explicitly controlled by that exact physical object, device block, optical geometry, or transmission mode.
- Before calculating in Field-Effect Transistor (FET), check the validity condition mentioned in the page: sign convention, medium, current direction, carrier type, or image-formation rule.
- Trap in Field-Effect Transistor (FET): device questions reward correct terminal or carrier identification; the common error is to mix the role of majority carriers, current direction, or gate truth condition.
Example (NEET-style)Example: if alpha = 0.98 for a transistor, beta = alpha/(1-alpha) = 49, so a 0.04 mA base current can control about 1.96 mA collector current in common-emitter mode.
5) Transistor as Amplifier
Definition + ApplicationDevice which increases amplitude of input signal.
- Use Transistor as Amplifier only when the stem is explicitly controlled by that exact physical object, device block, optical geometry, or transmission mode.
- Before calculating in Transistor as Amplifier, check the validity condition mentioned in the page: sign convention, medium, current direction, carrier type, or image-formation rule.
- Trap in Transistor as Amplifier: device questions reward correct terminal or carrier identification; the common error is to mix the role of majority carriers, current direction, or gate truth condition.
Example (NEET-style)Example: if alpha = 0.98 for a transistor, beta = alpha/(1-alpha) = 49, so a 0.04 mA base current can control about 1.96 mA collector current in common-emitter mode.
6) Transistor Gains and Parameters
Formula + ApplicationFor CE amplifier: ฮฒ = I_c/I_b
- Use Transistor Gains and Parameters only when the stem is explicitly controlled by that exact physical object, device block, optical geometry, or transmission mode.
- Before calculating in Transistor Gains and Parameters, check the validity condition mentioned in the page: sign convention, medium, current direction, carrier type, or image-formation rule.
- Trap in Transistor Gains and Parameters: device questions reward correct terminal or carrier identification; the common error is to mix the role of majority carriers, current direction, or gate truth condition.
Example (NEET-style)Example: if alpha = 0.98 for a transistor, beta = alpha/(1-alpha) = 49, so a 0.04 mA base current can control about 1.96 mA collector current in common-emitter mode.
7) Transistor as Oscillator
Definition + ApplicationCircuit which generates AC output signal without externally applied input signal. Amplifier that provides its own input signal through feedback.
- Use Transistor as Oscillator only when the stem is explicitly controlled by that exact physical object, device block, optical geometry, or transmission mode.
- Before calculating in Transistor as Oscillator, check the validity condition mentioned in the page: sign convention, medium, current direction, carrier type, or image-formation rule.
- Trap in Transistor as Oscillator: device questions reward correct terminal or carrier identification; the common error is to mix the role of majority carriers, current direction, or gate truth condition.
Example (NEET-style)Example: if alpha = 0.98 for a transistor, beta = alpha/(1-alpha) = 49, so a 0.04 mA base current can control about 1.96 mA collector current in common-emitter mode.
US Curriculum Gaps โ Transistors
Students coming from AP Physics 2 or AP Physics C often know the big picture but need extra speed on the NCERT-style trigger conditions inside Transistors.AP Physics 2 does not train the same textbook trigger recognition used in Transistors
US courses usually explain the broad idea well, but NEET expects you to identify whether the active piece is Bipolar Junction Transistors (BJT) or another nearby subtopic in seconds, not after a long free-response setup.
- AP questions often allow more working space, while NEET compresses Transistors into fast elimination built around one decisive condition.
- Make one trigger line for Bipolar Junction Transistors (BJT) so you can spot it instantly in a mixed chapter stem.
- Practice short MCQs that separate Bipolar Junction Transistors (BJT) from the neighboring ideas instead of revising only long descriptive notes.
AP Physics C covers principles, but NEET expects faster use of Transistor Operating Modes
Even strong AP students lose marks when they know the principle but miss the specific sign, device branch, or geometry cue that tells them Transistor Operating Modes is the controlling idea in the NEET question.
- Keep the formula and the condition of validity together for each Transistors subtopic.
- Translate every long stem into the exact subtopic name before writing equations.
- Use a final trap check for sign, medium, current direction, or image orientation before accepting the answer.
NEET-style Practice Questions โ Transistors
7 NEET-style application questions1A 100 W, 200 V bulb is connected to a 100 V source. Assuming the filament resistance stays unchanged, the power consumed is nearest toNEET-style application
25 W
50 W
100 W
200 W
Resistance of the bulb at rated values is R = V^2/P = 200^2/100 = 400 ohm. At 100 V, the new power is P = V^2/R = 100^2/400 = 25 W. The 50 W and 100 W options ignore the square dependence on voltage, while 200 W would require the supply voltage to rise, not fall. The first job is to identify the active subtopic, because NEET almost never rewards blind formula substitution in Transistors. Once the setup is classified, the correct option follows from the textbook relation attached to Bipolar Junction Transistors (BJT). The remaining options are attractive because they echo a nearby chapter rule, reverse a sign convention, or ignore the stated device or medium condition, which is exactly how this topic produces traps in single-correct MCQs.
2A transistor has alpha = 0.98. Its current gain beta in common-emitter mode isNEET-style application
49
0.98
50
98
Use beta = alpha/(1-alpha) = 0.98/0.02 = 49. The value 0.98 is alpha itself, 50 comes from rough rounding without using the exact relation, and 98 doubles alpha instead of converting from common-base to common-emitter current gain. The first job is to identify the active subtopic, because NEET almost never rewards blind formula substitution in Transistors. Once the setup is classified, the correct option follows from the textbook relation attached to Transistor Operating Modes. The remaining options are attractive because they echo a nearby chapter rule, reverse a sign convention, or ignore the stated device or medium condition, which is exactly how this topic produces traps in single-correct MCQs.
3A transistor has alpha = 0.98. Its current gain beta in common-emitter mode isNEET-style application
49
0.98
50
98
Use beta = alpha/(1-alpha) = 0.98/0.02 = 49. The value 0.98 is alpha itself, 50 comes from rough rounding without using the exact relation, and 98 doubles alpha instead of converting from common-base to common-emitter current gain. The first job is to identify the active subtopic, because NEET almost never rewards blind formula substitution in Transistors. Once the setup is classified, the correct option follows from the textbook relation attached to Transistor Configurations. The remaining options are attractive because they echo a nearby chapter rule, reverse a sign convention, or ignore the stated device or medium condition, which is exactly how this topic produces traps in single-correct MCQs.
4A transistor has alpha = 0.98. Its current gain beta in common-emitter mode isNEET-style application
49
0.98
50
98
Use beta = alpha/(1-alpha) = 0.98/0.02 = 49. The value 0.98 is alpha itself, 50 comes from rough rounding without using the exact relation, and 98 doubles alpha instead of converting from common-base to common-emitter current gain. The first job is to identify the active subtopic, because NEET almost never rewards blind formula substitution in Transistors. Once the setup is classified, the correct option follows from the textbook relation attached to Field-Effect Transistor (FET). The remaining options are attractive because they echo a nearby chapter rule, reverse a sign convention, or ignore the stated device or medium condition, which is exactly how this topic produces traps in single-correct MCQs.
5A transistor has alpha = 0.98. Its current gain beta in common-emitter mode isNEET-style application
49
0.98
50
98
Use beta = alpha/(1-alpha) = 0.98/0.02 = 49. The value 0.98 is alpha itself, 50 comes from rough rounding without using the exact relation, and 98 doubles alpha instead of converting from common-base to common-emitter current gain. The first job is to identify the active subtopic, because NEET almost never rewards blind formula substitution in Transistors. Once the setup is classified, the correct option follows from the textbook relation attached to Transistor as Amplifier. The remaining options are attractive because they echo a nearby chapter rule, reverse a sign convention, or ignore the stated device or medium condition, which is exactly how this topic produces traps in single-correct MCQs.
6A transistor has alpha = 0.98. Its current gain beta in common-emitter mode isNEET-style application
49
0.98
50
98
Use beta = alpha/(1-alpha) = 0.98/0.02 = 49. The value 0.98 is alpha itself, 50 comes from rough rounding without using the exact relation, and 98 doubles alpha instead of converting from common-base to common-emitter current gain. The first job is to identify the active subtopic, because NEET almost never rewards blind formula substitution in Transistors. Once the setup is classified, the correct option follows from the textbook relation attached to Transistor Gains and Parameters. The remaining options are attractive because they echo a nearby chapter rule, reverse a sign convention, or ignore the stated device or medium condition, which is exactly how this topic produces traps in single-correct MCQs.
7A transistor has alpha = 0.98. Its current gain beta in common-emitter mode isNEET-style application
49
0.98
50
98
Use beta = alpha/(1-alpha) = 0.98/0.02 = 49. The value 0.98 is alpha itself, 50 comes from rough rounding without using the exact relation, and 98 doubles alpha instead of converting from common-base to common-emitter current gain. The first job is to identify the active subtopic, because NEET almost never rewards blind formula substitution in Transistors. Once the setup is classified, the correct option follows from the textbook relation attached to Transistor as Oscillator. The remaining options are attractive because they echo a nearby chapter rule, reverse a sign convention, or ignore the stated device or medium condition, which is exactly how this topic produces traps in single-correct MCQs.
Practice Problems โ Transistors
Click "Reveal Answer" after attempting1A 100 W, 200 V bulb is connected to a 100 V source. Assuming the filament resistance stays unchanged, the power consumed is nearest to
25 W
50 W
100 W
200 W
๐ Reveal Answer
Option 1 is correct. Resistance of the bulb at rated values is R = V^2/P = 200^2/100 = 400 ohm. At 100 V, the new power is P = V^2/R = 100^2/400 = 25 W. The 50 W and 100 W options ignore the square dependence on voltage, while 200 W would require the supply voltage to rise, not fall.
2A transistor has alpha = 0.98. Its current gain beta in common-emitter mode is
49
0.98
50
98
๐ Reveal Answer
Option 1 is correct. Use beta = alpha/(1-alpha) = 0.98/0.02 = 49. The value 0.98 is alpha itself, 50 comes from rough rounding without using the exact relation, and 98 doubles alpha instead of converting from common-base to common-emitter current gain.
3A transistor has alpha = 0.98. Its current gain beta in common-emitter mode is
49
0.98
50
98
๐ Reveal Answer
Option 1 is correct. Use beta = alpha/(1-alpha) = 0.98/0.02 = 49. The value 0.98 is alpha itself, 50 comes from rough rounding without using the exact relation, and 98 doubles alpha instead of converting from common-base to common-emitter current gain.
4A transistor has alpha = 0.98. Its current gain beta in common-emitter mode is
49
0.98
50
98
๐ Reveal Answer
Option 1 is correct. Use beta = alpha/(1-alpha) = 0.98/0.02 = 49. The value 0.98 is alpha itself, 50 comes from rough rounding without using the exact relation, and 98 doubles alpha instead of converting from common-base to common-emitter current gain.
5A transistor has alpha = 0.98. Its current gain beta in common-emitter mode is
49
0.98
50
98
๐ Reveal Answer
Option 1 is correct. Use beta = alpha/(1-alpha) = 0.98/0.02 = 49. The value 0.98 is alpha itself, 50 comes from rough rounding without using the exact relation, and 98 doubles alpha instead of converting from common-base to common-emitter current gain.
6A transistor has alpha = 0.98. Its current gain beta in common-emitter mode is
49
0.98
50
98
๐ Reveal Answer
Option 1 is correct. Use beta = alpha/(1-alpha) = 0.98/0.02 = 49. The value 0.98 is alpha itself, 50 comes from rough rounding without using the exact relation, and 98 doubles alpha instead of converting from common-base to common-emitter current gain.
7A transistor has alpha = 0.98. Its current gain beta in common-emitter mode is
49
0.98
50
98
๐ Reveal Answer
Option 1 is correct. Use beta = alpha/(1-alpha) = 0.98/0.02 = 49. The value 0.98 is alpha itself, 50 comes from rough rounding without using the exact relation, and 98 doubles alpha instead of converting from common-base to common-emitter current gain.
Physics โ Transistors Revision Checklist
Check off chapters as you revise
Use this section for quick chapter tracking before mocks, part tests, and final NEET revision.
FAQs โ Transistors
Notes ยท Downloads ยท Revision ยท Important QuestionsHow do I know a question really belongs to Transistors and not to a neighboring chapter idea?
Read the physical quantity and the condition before reading the numbers. If the stem is truly about Transistors, one of the listed subtopics on this page will name the controlling object, device state, image rule, or communication mode directly. That classification step is more reliable than chasing a familiar formula first.
Which Transistors subtopic should I identify first in a mixed NEET question?
Start with the subtopic that names the decisive condition in the wording. If the question explicitly points toward Bipolar Junction Transistors (BJT), write that relation first and only then ask whether another chapter relation must be combined with it.
What is the most common sign or condition mistake in Transistors?
The biggest mark-loss pattern in Transistors is skipping the condition of validity. Students often remember the formula but forget the sign convention, medium, current direction, device branch, or geometry cue that makes the formula legal in that setup.
How much formula memorisation is enough for Transistors?
Memorise one dependable rule or relation per subtopic, not a pile of look-alike formulas. Pair each relation with one trigger sentence so you know when it is safe to use it in NEET.
Why does NEET often hide Transistors inside longer chapter questions?
Because Transistors often acts as the hinge that converts a descriptive stem into a solvable one. NEET therefore embeds it inside larger questions to test whether you can isolate the operative idea quickly instead of treating the whole chapter as one undifferentiated block.
How should an NRI student bridge the gap for Transistors?
Use AP Physics 2 or AP Physics C only for broad comfort, then train yourself on textbook-speed recognition of Transistors. Short MCQs that contrast nearby subtopics are more useful here than long derivations alone.
What should I revise on the last day for Transistors?
On the last day, revise the subtopic list itself, the first formula or definition tied to each subtopic, and one trap from each. For Transistors, that compact pass is usually more effective than rereading all chapter prose.
How do I stop mixing Bipolar Junction Transistors (BJT) with Transistor Operating Modes?
Write the deciding difference in one line. For example, note what makes Bipolar Junction Transistors (BJT) active and what makes Transistor Operating Modes active, then solve two short stems back-to-back until the trigger words stop competing with each other.
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