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A.c. and D.c.
D.c. flows in one direction; a.c. reverses periodically.
Choose Your Level
A.c. and D.c.
A battery gives current mainly in one direction: d.c.
Mains electricity keeps reversing direction: a.c.
Recommended for Class 10
A.c. and D.c.
This topic compares alternating current and direct current.
D.c.
Direction → one direction.
Common sources → cells, batteries, solar cells.
Typical use → electronics and battery-powered systems.
A.c.
Direction → reverses periodically.
Common source → electrical generators and mains supply.
Typical use → electrical power transmission and distribution.
Comparison
Direction
D.c. → fixed overall direction.
A.c. → reverses.
Waveform
Ideal constant d.c. → horizontal line.
Sinusoidal a.c. → alternating positive and negative values.
Transformers
A.c. can be conveniently stepped up or down using transformers.
Steady d.c. cannot be transformed by an ordinary transformer without first being switched or converted.
Why Both Are Used
A.c. is highly convenient for large-scale power distribution.
D.c. is widely used by electronic devices, batteries, and many low-voltage systems.
Modern electrical systems often convert between the two.
A.c. and D.c. — Advanced
The distinction concerns time dependence and polarity.
Power-electronic converters can rectify a.c. to d.c. and invert d.c. to a.c., allowing modern systems to use whichever form is most suitable.
Common Mistakes
Common Mistakes
- Mistake
A.c. is not automatically more dangerous simply because it alternates; electrical risk depends on voltage, current, path, duration, frequency, and other factors.
- Mistake
D.c. does not mean “no voltage change under any circumstance.”
Revision Zone
60-Second Revision
Quick cues from this topic — use them for last-minute revision.
D.c. → one direction.
A.c. → reverses.
Battery → d.c.
Mains → generally a.c.
- Definition
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Practice
PQ
Q1. State the main difference between a.c. and d.c.
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Q2. Give a common d.c. source.
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Q3. Give a common a.c. source/application.
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Q4. Why is a.c. convenient in power distribution?
PQ
Q5. What does a rectifier do?
Exam Practice
EQ
Q1. Differentiate a.c. and d.c.
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Q2. Sketch/describe their waveforms.
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Q3. Give two sources/applications of each.
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Q4. Explain why transformers favour a.c. transmission systems.
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Q5. State the functions of a rectifier and inverter.
School-standard facts for Matric and Intermediate. Original explanations — not copied from textbooks.