Class 12 Physics — Chapter 7: ALTERNATING CURRENT
Chapter 7: ALTERNATING CURRENT is a chapter in Class 12 Physics (Part 1), part of the CBSE NCERT curriculum followed by over 25 million students across India. This chapter covers 6 topics including Introduction to Alternating Current (AC), AC Voltage Applied to a Pure Resistor, Root Mean Square (RMS) Values. BrainWeave provides free AI-powered explanations — by voice or text, in Hindi or English — with no signup required.
What you'll learn
-
▸Introduction to Alternating Current (AC)alternating currentdirect currentsinusoidal voltagetransformerpower transmission
-
▸AC Voltage Applied to a Pure ResistorCore conceptpure resistorin phaseOhm's lawphase angleKirchhoff's rule
-
▸Root Mean Square (RMS) ValuesCore conceptRMS currentRMS voltageeffective valuepeak voltageroot mean square
-
▸Power in AC CircuitsCore conceptaverage powerinstantaneous powerpower dissipationJoule heatingpower factor
-
▸Phasor DiagramsCore conceptphasorphasor diagramrotating vectorphase relationshipamplitude
-
▸AC Voltage Applied to a Pure InductorCore conceptpure inductorinductive reactancecurrent lagsphase differenceinduced EMF
Chapter Summary
Understand the fundamental difference between alternating current (AC) and direct current (DC), including the sinusoidal nature of AC voltage (v = vm sin ωt). Learn the primary advantages of AC, such as efficient voltage conversion with transformers and economical long-distance power transmission.
Analyze a purely resistive AC circuit. Understand that the current and voltage are in phase, meaning they reach their maximum and zero values simultaneously. Apply Ohm's law to the peak values (im = vm/R) and RMS values (V=IR).
Define and understand the concept of Root Mean Square (RMS) or 'effective' values for AC voltage and current. Learn the relationship between RMS and peak values (I = im/√2, V = vm/√2) and why RMS values are the standard for specifying AC quantities like household voltage.
Understand how power is dissipated in an AC circuit. Differentiate between instantaneous power and average power. Learn to calculate the average power in a resistive circuit using both peak values (P = ½ i_m² R) and RMS values (P = I²R = V²/R).
Learn to represent sinusoidally varying AC quantities (voltage and current) as rotating vectors called phasors. Understand that a phasor's length represents the amplitude (peak value) and its projection on the vertical axis represents the instantaneous value, which helps visualize the phase relationship between different quantities.
Analyze a purely inductive AC circuit. Understand the relationship between the applied voltage and the self-induced EMF using Kirchhoff's rule (v = L di/dt). This leads to the crucial understanding that the current lags behind the voltage by a phase angle of 90 degrees (π/2).
Practice Questions from this Chapter
Tap "Get Solution" on any question to ask our AI tutor.
- Explain alternating current simply. Get Solution →
- Describe how transformers work? Get Solution →
- Compare AC versus DC power. Get Solution →
- What is a voltage that varies like a sine function with time called? Get Solution →
- What is the main reason mentioned in the text for preferring AC voltage over DC voltage for power distribution? Get Solution →
- What is the symbol for an AC source in a circuit diagram? Get Solution →
- In a purely resistive AC circuit, what is the phase relationship between the voltage and the current? Get Solution →
- What is the average value of alternating current over one complete cycle? Get Solution →
Did you know?
- 💡 Thomas Edison once electrocuted animals to make people fear alternating current.
- 💡 Nicola Tesla imagined a global wireless power system, but it was never built.
- 💡 The electricity in your wall outlet switches direction 100 or 120 times each second.
- 💡 Electricity flows through wires incredibly fast, nearly the speed of light.
- 💡 A single bolt of lightning contains enough energy to power a city for days.
Frequently Asked Questions
How many topics are covered in this chapter?
This chapter covers 6 key topics: Introduction to Alternating Current (AC), AC Voltage Applied to a Pure Resistor, Root Mean Square (RMS) Values, Power in AC Circuits, Phasor Diagrams, and more. The BrainWeave AI tutor explains each one with examples.
Is Chapter 7: ALTERNATING CURRENT important for board exams?
Yes — Class 12 is a CBSE board exam year, and every NCERT chapter is part of the syllabus. Use BrainWeave's AI tutor to master this chapter, then practice with the auto-generated quizzes and mind maps.
Can I get NCERT solutions for this chapter in Hindi?
Yes. BrainWeave's AI tutor supports Hindi, English, and Hinglish for both voice and text chat. Just ask your question in your preferred language.
Is BrainWeave free for Class 12 - Science?
Yes. BrainWeave's free Spark plan gives generous daily messages — enough for regular homework. Premium features unlock when you bring your own free Google Gemini API key.
Can I use voice chat for this chapter?
Absolutely. Tap the mic, ask any question about Chapter 7: ALTERNATING CURRENT, and the AI tutor will explain it back in voice and text.
How is BrainWeave better than static NCERT solutions sites?
Static solution sites give the same answer to everyone. BrainWeave adapts to your question — ask "explain like I'm 12" or "give a real-world example" and get a personalized response. Voice mode and Hindi support work seamlessly.
Related Chapters
Ask Any Question About Chapter 7: ALTERNATING CURRENT
Voice or text. Hindi or English. Free to start. No signup required.
Start Now →