Sit a full NEET(UG) paper, free
45 questions, 45 minutes, out of 180, marked the way the exam marks it. No payment, no card, and no account needed to start.
1,000 XP coins free the first time you open your portal — enough to open a whole chapter level there and then.
Alternating Current looks heavier than it is. Once you accept that a resistor, an inductor and a capacitor each treat an alternating voltage differently, the whole chapter reduces to three reactances, one impedance formula and the resonance condition. NEET(UG) asks very standard questions here, and a student who knows the phase relations cold rarely drops a mark. Ten questions below. Give them ten honest minutes.
What this chapter carries in NEET(UG)
- Usually 2 to 3 questions every year, which is 8 to 12 marks.
- Series LCR, resonance and impedance are the regular questions.
- Power factor, rms values and the transformer fill the rest.
What the syllabus says
In the syllabus (Unit 14, Electromagnetic Induction and Alternating Currents): Alternating currents, peak and RMS values of alternating current and voltage, reactance and impedance, the LCR series circuit and resonance, power in AC circuits, wattless current, the AC generator and the transformer.
Taken out in 2024: quality factor.
Taken from the NMC syllabus for NEET (UG) 2026, the latest one published. See the full syllabus, unit by unit.
Formulas you must know by heart
| Instantaneous current | I = I0 sinωt |
| Root mean square values | Irms = I0/√2, Vrms = V0/√2 |
| Average over a half cycle | Iav = 2I0/π |
| Inductive reactance | XL = ωL |
| Capacitive reactance | XC = 1/ωC |
| Impedance | Z = √(R2 + (XL − XC)2) |
| Phase angle | tanφ = (XL − XC)/R |
| Resonance | XL = XC, f = 1/(2π√(LC)) |
| Average power | P = VrmsIrms cosφ |
| Transformer | Vs/Vp = Ns/Np = Ip/Is |
| Power factor | cosφ = R/Z |
The power formula is the one to understand rather than memorise. A pure inductor or a pure capacitor has φ = 90°, so cosφ = 0 and it consumes nothing over a full cycle. It borrows energy for half the cycle and gives all of it back in the other half.
Ten questions. Give yourself ten minutes.
Write your answers down before you scroll. A question you looked up is a question you have not answered.
Q1. The peak value of an alternating current is 2 A. Its rms value is about
- (a) 2 A
- (b) 1.414 A
- (c) 2.828 A
- (d) 1 A
Q2. In a purely inductive circuit, the current
- (a) leads the voltage by π/2
- (b) lags the voltage by π/2
- (c) is in phase with the voltage
- (d) lags the voltage by π
Q3. As the frequency of the supply rises, the capacitive reactance of a capacitor
- (a) increases
- (b) decreases
- (c) stays the same
- (d) becomes zero
Q4. At resonance in a series LCR circuit, the impedance is
- (a) maximum
- (b) minimum
- (c) zero at all frequencies
- (d) equal to XL
Q5. If both L and C in a series circuit are doubled, the resonant frequency becomes
- (a) double
- (b) half
- (c) four times
- (d) unchanged
Q6. The power factor of a purely resistive circuit is
- (a) 0
- (b) 1
- (c) 0.5
- (d) infinite
Q7. The average power consumed over a full cycle in a purely inductive circuit is
- (a) VI
- (b) zero
- (c) ½VI
- (d) VI cosφ
Q8. In a step-up transformer
- (a) the voltage rises and the current falls
- (b) both the voltage and the current rise
- (c) the voltage falls and the current rises
- (d) both fall
Q9. The impedance of a series LCR circuit is given by
- (a) R + XL + XC
- (b) √(R2 + (XL − XC)2)
- (c) √(R2 + XL2 + XC2)
- (d) R alone
Q10. The SI unit of impedance is the
- (a) henry
- (b) farad
- (c) ohm
- (d) watt
Answer key, with a hint for each
| Q1 | (b) | Irms = I0/√2 = 2/1.414. |
| Q2 | (b) | An inductor fights any change in current, so the current is always running a quarter cycle behind the voltage. |
| Q3 | (b) | XC = 1/ωC. A capacitor passes high frequencies easily and blocks direct current completely. |
| Q4 | (b) | XL and XC cancel, leaving Z = R, which is the smallest it can be. The current is then largest. |
| Q5 | (b) | f ∝ 1/√(LC). Doubling both doubles √(LC), so f halves. |
| Q6 | (b) | There is no phase difference in a resistor, so cos 0° = 1 and all the power is used. |
| Q7 | (b) | cos 90° = 0. The current here is called a wattless current for exactly that reason. |
| Q8 | (a) | Power is conserved, so if the voltage goes up the current must come down. A transformer cannot create energy. |
| Q9 | (b) | R and the net reactance add like two sides of a right-angled triangle, not as plain numbers. |
| Q10 | (c) | Impedance, reactance and resistance all share the same unit. |
Now mark yourself honestly
NEET(UG) marks the way it marks. Use the same rule here:
- +4 for a right answer
- −1 for a wrong one
- 0 for a blank
So ten questions here are out of 40. In the real paper, 45 Physics questions are out of 180.
If you scored 32 or more, the basics of this chapter are secure. Move to harder questions, not more of these.
If you scored below 24, do not feel bad about it. You have just found out something useful before the exam did. Go back to the formula table above, learn it properly, and sit these ten again tomorrow.
And if you guessed a few and they landed, count those as wrong. A guess that works once will not work in May.
The full chapter, on a clock
Ten questions tell you a little. Forty-five tell you the truth.
The Beginner paper for Alternating Current is waiting for you on the portal: 45 questions, 45 minutes, marked out of 180, with the answer key and a hint for every question. Sit it tonight and you will know exactly where this chapter stands.
Free the moment you register
1,000 XP coins, free
A Foundation paper opens for 230 coins, so your first four are already paid for. And every paper you sit sincerely pays you more.
Every chapter of NEET(UG) Physics has three papers on the portal: Beginner, Intermediate and Expert. You move up only when you clear the one below. 30 chapters, 90 papers, open 24×7.
Want to know how many marks this chapter usually carries? See the NEET Physics chapter-wise weightage.
All the formulas for every chapter in one place: NEET Physics formula sheet.
One NEET(UG) Physics question every morning
It comes at 7 AM on Telegram. Tap the option you think is right and you will know at once whether it was. The worked hint follows the next morning.