Why does an operational amplifier need two power supplies?

Related questions

1. Why feedback is used in op amp?
2. Which feedback is used in amplifiers?
3. What is the function of offset pin in IC 741?
4. What is the difference between transistor and amplifier?
5. Is op amp a linear device?
6. Is transistor A linear device?
7. Can we amplify DC signal?
8. Why op amps are called linear devices?
9. Does resistor limit voltage?
10. What is the difference between amplifier and operational amplifier?

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