AC Current vs DC Current – Class 12 Physics Easy Explanation
- Admin
- 13 minutes ago
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When we study Class 12 Physics, we come across two types of current:
DC Current (Direct Current)
AC Current (Alternating Current)
DC Current (Direct Current)
DC current is produced by a battery.
A battery has two polarities → positive and negative.
In DC circuits, we mainly use resistors.
Reason: Resistors follow Ohm’s Law and always obey it.
That is why, in most DC circuits, resistance is the main element.
AC Current (Alternating Current)
AC is represented by a sine waveform:
V=V0sin(ωt)V = V_0 \sin(\omega t)V=V0sin(ωt)
In India, the domestic AC supply is:
220 Volts (RMS value)
50 Hz frequency
This means the voltage keeps changing with time in a sine wave pattern.
Why Do We Use AC Instead of DC?
Compatibility with Components
AC works with resistors, inductors, and capacitors.
DC does not work properly with inductors and capacitors.
For inductors → DC has zero frequency, so there is no rate of change of flux.
For capacitors → DC charges them once, then no current flows.
Vector Nature of AC
AC is treated as a vector (phasor) quantity.
Example: In a three-phase AC supply, three waveforms are separated by 120°.
Their resultant current in the neutral wire = 0, so the neutral wire can be thin and cheap.
In industries, this three-phase system saves cost and improves efficiency.
Easy Transmission (Step-Up and Step-Down)
AC can be stepped up or stepped down using a transformer.
DC cannot be stepped up or down easily. This makes DC transmission costly and inefficient.
Can AC Be Stored?
AC cannot be stored directly.
Example: A mobile charger has an adapter.
The adapter converts AC into DC.
Only DC is stored in the mobile battery.
If we calculate the average value of AC over a complete cycle, it is always zero.
Vavg=0V_{\text{avg}} = 0Vavg=0
That is why only DC can be stored in batteries, not AC.
AC vs DC in Power Distribution
Domestic Supply (homes): 2 wires (Phase + Neutral).
Industrial Supply: 3 Phase wires (Red, Yellow, Blue) + Neutral.
With AC, neutral carries zero current → thin and cheap wire.
With DC, for three-phase equivalent → 6 wires of equal thickness are needed → very costly.
AC in Semiconductor Devices
Our devices like TV, computer, refrigerators are built using semiconductors.
These are designed to work well with AC.
Designing them for DC is not as efficient or cost-effective.
✅ Final Conclusion
DC Current: Produced by batteries, follows Ohm’s law, can be stored in capacitors and batteries.
AC Current: Sine waveform, cannot be stored directly, but used in power supply, transmission, and industries.
AC is better for transmission because it can be stepped up or down, works with inductors & capacitors, and reduces cost in three-phase systems.
That is why AC is the main source of electricity in our homes and industries, while DC is used for storage in batteries.
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