Chapter 13 

āĻ…āϧ্āϝাāϝ় ā§§ā§Š

Magnetic Electric Current

āϚুāĻŽ্āĻŦāĻ•ীāϝ় āĻŦৈāĻĻ্āϝুāϤিāĻ• āĻĒ্ā§°āĻŦাāĻš

EXERCISES

āĻŦ্āϝাāϝ়াāĻŽ 

 1. Which of the following correctly describes the magnetic field near a long straight wire? 

1. āϤāϞ⧰ āĻ•োāύāϟোā§ąে āĻĻীāϘāϞ āĻĒোāύ āϤাঁā§°ā§° āĻ“āϚ⧰⧰ āϚুāĻŽ্āĻŦāĻ•ীāϝ় āĻ•্āώেāϤ্ā§°āĻ–āύ āϏāĻ িāĻ•āĻ­াā§ąে āĻŦā§°্āĻŖāύা āϕ⧰িāĻ›ে?

(a) The field consists of straight lines perpendicular to the wire,

(āĻ•) āĻ•্āώেāϤ্ā§°āĻ–āύ āϤাঁā§°ā§° āϞāĻ—āϤ āϞāĻŽ্āĻŦāĻ­াā§ąে āĻĨāĻ•া āϏ⧰āϞ⧰েāĻ–াā§°ে āĻ—āĻ িāϤ, 

(b) The field consists of straight lines parallel to the wire.

(āĻ–) āĻ•্āώেāϤ্ā§°āĻ–āύ āϤাঁā§°ā§° āϏāĻŽাāύ্āϤ⧰াāϞāĻ­াā§ąে āϏ⧰āϞ⧰েāĻ–াā§°ে āĻ—āĻ িāϤ।

 (c) The field consists of radial lines originating from the wire.

(āĻ—) āϤাঁā§°ā§° āĻĒā§°া āĻ‰ā§ŽāĻĒāϤ্āϤি āĻšোā§ąা ā§°েāĻĄিāϝ়েāϞ ā§°েāĻ–াā§°ে āĻ•্āώেāϤ্ā§°āĻ–āύ āĻ—āĻ িāϤ।

 (d) The field consists of concentric circles centred on the wire.

(āϘ) āϤাঁā§°ā§° āĻ“āĻĒā§°āϤ āĻ•েāύ্āĻĻ্ā§° āϕ⧰ি āϏāĻŽāĻ•েāύ্āĻĻ্ā§°িāĻ• āĻŦৃāϤ্āϤ⧰ে āĻ•্āώেāϤ্ā§°āĻ–āύ āĻ—āĻ িāϤ।

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2. The phenomenon of electromagnetic induction is

⧍/ āĻŦিāĻĻ্āϝুā§ŽāϚুāĻŽ্āĻŦāĻ•ীāϝ় āĻĒ্ā§°ā§°োāϚāύাā§° āĻĒā§°িāϘāϟāύাāϟো āĻš’āϞ

 (a) the process of charging a body.

(āĻ•) āĻ•োāύো āĻŦāϏ্āϤুāĻ• āϚাā§°্āϜ āϕ⧰াā§° āĻĒ্ā§°āĻ•্ā§°িāϝ়া।

 (b) the process of generating magnetic field due to a current passing through a coil.

(āĻ–) āĻ•ুāĻŖ্āĻĄāϞীā§° āĻŽাāϜেā§°ে āĻĒাā§° āĻšৈ āϝোā§ąা āĻŦিāĻĻ্āϝুā§Ž āĻĒ্ā§°āĻŦাāĻšā§° āĻĢāϞāϤ āϚুāĻŽ্āĻŦāĻ•ীāϝ় āĻ•্āώেāϤ্ā§° āĻ‰ā§ŽāĻĒāύ্āύ āϕ⧰া āĻĒ্ā§°āĻ•্ā§°িāϝ়া।

 (c) producing induced current in a coil due to relative motion between a magnet and the coil.

(āĻ—) āϚুāĻŽ্āĻŦāĻ• āφ⧰ু āĻ•ুāĻŖ্āĻĄāϞীā§° āĻŽাāϜāϤ āφāĻĒেāĻ•্āώিāĻ• āĻ—āϤিā§° āĻŦাāĻŦে āĻ•ুāĻŖ্āĻĄāϞীāϤ āĻĒ্ā§°ā§°োāϚিāϤ āĻŦিāĻĻ্āϝুā§Ž āĻĒ্ā§°āĻŦাāĻš āĻ‰ā§ŽāĻĒāύ্āύ āϕ⧰া।

 (d) the process of rotating a coil of an electric motor.

(āϘ) āĻŦৈāĻĻ্āϝুāϤিāĻ• āĻŽāϟ⧰⧰ āĻāϟা āĻ•āχāϞ āϘূā§°োā§ąাā§° āĻĒ্ā§°āĻ•্ā§°িāϝ়া।

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3. The device used for producing electric current is called a

ā§Š) āĻŦৈāĻĻ্āϝুāϤিāĻ• āĻĒ্ā§°āĻŦাāĻš āĻ‰ā§ŽāĻĒāύ্āύ āϕ⧰িāĻŦāϞৈ āĻŦ্āĻ¯ā§ąāĻšাā§° āϕ⧰া āϝāύ্āϤ্ā§°āϟোāĻ• āĻ• āĻŦোāϞা āĻšāϝ়

 (a) generator.

(āĻ•) āϜেāύেā§°েāϟ⧰।

 (b) galvanometer.

(āĻ–) āĻ—েāϞāĻ­েāύ’āĻŽিāϟাā§°।

 (c) ammeter.

(āĻ—) āĻāĻŽিāϟাā§°।

 (d) motor.

(āϘ) āĻŽāϟ⧰।

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4. The essential difference between an AC generator and a DC generator is that 

ā§Ē/ āĻ āϚি āϜেāύেā§°েāϟ⧰ āφ⧰ু āĻĄি āϚি āϜেāύেā§°েāϟ⧰⧰ āĻŽাāϜāϤ āĻĨāĻ•া āĻ…āĻĒā§°িāĻšাā§°্āϝ āĻĒাā§°্āĻĨāĻ•্āϝāϟো āĻš’āϞ

(a) AC generator has an electromagnet while a DC generator has permanent magnet.

(āĻ•) āĻ āϚি āϜেāύেā§°েāϟ⧰āϤ āĻŦিāĻĻ্āϝুā§ŽāϚুāĻŽ্āĻŦāĻ• āĻĨাāĻ•ে āφāύāĻšাāϤে āĻĄি āϚি āϜেāύেā§°েāϟ⧰āϤ āϏ্āĻĨাāϝ়ী āϚুāĻŽ্āĻŦāĻ• āĻĨাāĻ•ে।

 (b) DC generator will generate a higher voltage.

(āĻ–) āĻĄিāϚি āϜেāύেā§°েāϟ⧰ে āĻ…āϧিāĻ• āĻ­āϞ্āϟেāϜ āĻ‰ā§ŽāĻĒāύ্āύ āϕ⧰িāĻŦ।

 (c) AC generator will generate a higher voltage.

(āĻ—) āĻ āϚি āϜেāύেā§°েāϟ⧰ে āĻ…āϧিāĻ• āĻ­āϞ্āϟেāϜ āĻ‰ā§ŽāĻĒāύ্āύ āϕ⧰িāĻŦ।

 (d) AC generator has slip rings while the DC generator has a commutator.

(āϘ) āĻ āϚি āϜেāύেā§°েāϟ⧰āϤ āϏ্āϞিāĻĒ ā§°িং āĻĨাāĻ•ে āφāύāĻšাāϤে āĻĄি āϚি āϜেāύেā§°েāϟ⧰āϤ āĻ•āĻŽিāωāϟেāϟ⧰ āĻĨাāĻ•ে।

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5. At the time of short circuit, the current in the circuit

ā§Ģ) āĻļ্āĻŦā§°্āϟ āϚাā§°্āĻ•িāϟ⧰ āϏāĻŽāϝ়āϤ āϚাā§°্āĻ•িāϟāϤ āĻĨāĻ•া āĻ•াā§°েāĻŖ্āϟ

 (a) reduces substantially.

(āĻ•) āϝāĻĨেāώ্āϟ āĻĒā§°িāĻŽাāĻŖে āĻš্ā§°াāϏ āĻĒাāϝ়।

 (b) does not change.

(āĻ–) āϏāϞāύি āύāĻšāϝ়।

 (c) increases heavily.

(āĻ—) āĻŦāĻšু āĻĒā§°িāĻŽাāĻŖে āĻŦৃāĻĻ্āϧি āĻĒাāϝ়।

 (d) vary continuously.

(āϘ) āĻ…āĻŦিā§°āϤāĻ­াā§ąে āϤাā§°āϤāĻŽ্āϝ āϘāϟে।

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6. State whether the following statements are true or false.

ā§Ŧ) āϤāϞāϤ āĻĻিāϝ়া āĻŦāĻ•্āϤāĻŦ্āϝāĻŦোā§° āϏঁāϚা āύে āĻŽিāĻ›া āϏেāχāϟো āĻ•োā§ąা।

 (a) An electric motor converts mechanical energy into electrical energy.

(āĻ•) āĻŦৈāĻĻ্āϝুāϤিāĻ• āĻŽāϟ⧰ āĻāϟাāχ āϝাāύ্āϤ্ā§°িāĻ• āĻļāĻ•্āϤিāĻ• āĻŦৈāĻĻ্āϝুāϤিāĻ• āĻļāĻ•্āϤিāϞৈ ā§°ূāĻĒাāύ্āϤ⧰িāϤ āϕ⧰ে।

 (b) An electric generator works on the principle of electromagnetic induction.

(āĻ–) āĻāϟা āĻŦৈāĻĻ্āϝুāϤিāĻ• āĻ‰ā§ŽāĻĒাāĻĻāĻ•ে āĻŦিāĻĻ্āϝুā§ŽāϚুāĻŽ্āĻŦāĻ•ীāϝ় āĻĒ্ā§°ā§°োāϚāύাā§° āύীāϤিā§° āĻ“āĻĒā§°āϤ āĻ•াāĻŽ āϕ⧰ে।

 (c) The field at the centre of a long circular coil carrying current will be parallel straight lines.

(āĻ—) āĻ•াā§°েāĻŖ্āϟ āĻ•āĻĸ়িāϝ়াāχ āύিāϝ়া āĻĻীāϘāϞ āĻŦৃāϤ্āϤাāĻ•াā§° āĻ•ুāĻŖ্āĻĄāϞীā§° āĻ•েāύ্āĻĻ্ā§°āϤ āĻĨāĻ•া āĻ•্āώেāϤ্ā§°āĻ–āύ āϏāĻŽাāύ্āϤ⧰াāϞ āϏ⧰āϞ⧰েāĻ–া āĻš’āĻŦ।

 (d) A wire with a green insulation is usually the live wire of an electric supply.

 (āϘ) āϏেāωāϜীāϝ়া āχāύāϚুāϞেāϚāύ āĻĨāĻ•া āϤাঁā§° āĻšৈāĻ›ে āϏাāϧাā§°āĻŖāϤে āĻŦৈāĻĻ্āϝুāϤিāĻ• āϝোāĻ—াāύ⧰ āϜীā§ąāύ্āϤ āϤাঁā§°।

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7. List two methods of producing magnetic fields.

ā§­) āϚুāĻŽ্āĻŦāĻ•ীāϝ় āĻ•্āώেāϤ্ā§° āĻ‰ā§ŽāĻĒāύ্āύ āϕ⧰াā§° āĻĻুāϟা āĻĒāĻĻ্āϧāϤি āϤাāϞিāĻ•াāĻ­ুāĻ•্āϤ āϕ⧰া।

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8. How does a solenoid behave like a magnet? Can you determine the north and south poles of a current-carrying solenoid with the help of a bar magnet? Explain.

ā§Ž/ āĻ›’āϞেāύ’āχāĻĄে āϚুāĻŽ্āĻŦāϕ⧰ āĻĻā§°ে āĻ•েāύেāĻ•ৈ āφāϚ⧰āĻŖ āϕ⧰ে? āĻŦাā§° āϚুāĻŽ্āĻŦāϕ⧰ āϏāĻšাāϝ়āϤ āĻ•াā§°েāĻŖ্āϟ āĻ•āĻĸ়িāϝ়াāχ āύিāϝ়া āĻ›’āϞেāύ’āχāĻĄā§° āωāϤ্āϤ⧰ āφ⧰ু āĻĻāĻ•্āώিāĻŖ āĻŽেā§°ু āύিā§°্āĻŖāϝ় āϕ⧰িāĻŦ āĻĒাā§°িāĻŦāύে? āĻŦ্āϝাāĻ–্āϝা āϕ⧰া.

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9. When is the force experienced by a current-carrying conductor placed in a magnetic field largest?

⧝) āϚুāĻŽ্āĻŦāĻ•ীāϝ় āĻ•্āώেāϤ্ā§°āϤ āϏ্āĻĨাāĻĒāύ āϕ⧰া āĻŦিāĻĻ্āϝুā§Ž āĻĒ্ā§°āĻŦাāĻš āĻŦāĻšāύāĻ•াā§°ী āĻĒā§°িāĻŦাāĻšীāϝ়ে āĻ…āύুāĻ­ā§ą āϕ⧰া āĻŦāϞ āĻ•েāϤিāϝ়া āφāϟাāχāϤāĻ•ৈ āĻĄাāϙ⧰ āĻšāϝ়?

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10. Imagine that you are sitting in a chamber with your back to one wall. An electron beam, moving horizontally from back wall towards the front wall, is deflected by a strong magnetic field to your right side. What is the direction of magnetic field?

ā§§ā§Ļ) āĻ•āϞ্āĻĒāύা āϕ⧰āĻ• āϝে āφāĻĒুāύি āĻāϟা āĻ•োāĻ াāϤ āĻāϟা āĻŦেā§°āϤ āĻĒিāĻ ি āĻĻি āĻŦāĻšি āφāĻ›ে। āĻĒিāĻ›āĻĢাāϞ⧰ āĻŦেā§°ā§° āĻĒā§°া āϏāύ্āĻŽুāĻ–ā§° āĻŦেā§°ā§° āĻĢাāϞে āĻ…āύুāĻ­ূāĻŽিāĻ•āĻ­াā§ąে āĻ—āϤি āϕ⧰া āĻāϟা āχāϞেāĻ•্āϟ্ā§°āύ ā§°āĻļ্āĻŽি āĻāϟা āĻļāĻ•্āϤিāĻļাāϞী āϚুāĻŽ্āĻŦāĻ•ীāϝ় āĻ•্āώেāϤ্ā§°ā§° āĻĻ্āĻŦাā§°া āφāĻĒোāύাā§° āϏোঁāĻĢাāϞে āĻŦিāϚ্āϝুāϤ āĻšāϝ়। āϚুāĻŽ্āĻŦāĻ•ীāϝ় āĻ•্āώেāϤ্ā§°ā§° āĻĻিāĻļ āĻ•ি?

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11. Draw a labelled diagram of an electric motor. Explain its principle and working. What is the function of a split ring in an electric motor?

ā§§ā§§) āĻāϟা āĻŦৈāĻĻ্āϝুāϤিāĻ• āĻŽāϟ⧰⧰ āϞেāĻŦেāϞāϝুāĻ•্āϤ āĻĄাāϝ়েāĻ—্ā§°াāĻŽ āφঁāĻ•িāĻŦ। āχāϝ়াā§° āύীāϤি āφ⧰ু āĻ•াāĻŽ āϕ⧰া āĻŦ্āϝাāĻ–্āϝা āϕ⧰া। āĻŦৈāĻĻ্āϝুāϤিāĻ• āĻŽāϟ⧰āϤ āĻāϟা āĻŦিāĻ­āĻ•্āϤ āφāĻ™āĻ িā§° āĻ•াā§°্āϝ্āϝ āĻ•ি?

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12. Name some devices in which electric motors are used.

⧧⧍) āχāϞেāĻ•্āϟ্ā§°িāĻ• āĻŽāϟ⧰ āĻŦ্āĻ¯ā§ąāĻšাā§° āϕ⧰া āĻ•িāĻ›ুāĻŽাāύ āϝāύ্āϤ্ā§°ā§° āύাāĻŽ āϞিāĻ–া।

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13. A coil of insulated copper wire is connected to a galvanometer. What will happen if a bar magnet is (i) pushed into the coil, (ii) withdrawn from inside the coil, (iii) held stationary inside the coil?

ā§§ā§Š) āχāύāϚুāϞেāϟেāĻĄ āϤাāĻŽā§° āϤাঁā§°ā§° āĻāϟা āĻ•ুāĻŖ্āĻĄāϞী āĻ—েāϞāĻ­েāύ’āĻŽিāϟাā§°ā§° āϏৈāϤে āϏংāϝোāĻ— āϕ⧰া āĻšāϝ়। āϝāĻĻি āĻāϟা āĻŦাā§° āϚুāĻŽ্āĻŦāĻ• (i) āĻ•ুāĻŖ্āĻĄāϞীā§° āĻ­িāϤ⧰āϞৈ āĻ েāϞি āĻĻিāϝ়া āĻšāϝ়, (ii) āĻ•ুāĻŖ্āĻĄāϞীā§° āĻ­িāϤ⧰⧰ āĻĒā§°া āωāϞিāϝ়াāχ āĻĻিāϝ়া āĻšāϝ়, (iii) āĻ•ুāĻŖ্āĻĄāϞীā§° āĻ­িāϤ⧰āϤ āϏ্āĻĨāĻŦিā§° āϕ⧰ি ā§°āĻ–া āĻšāϝ় āϤেāύ্āϤে āĻ•ি āĻš’āĻŦ?

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14. Two circular coils A and B are placed closed to each other. If the current in the coil A is changed, will some current be induced in the coil B? Give reason.

ā§§ā§Ē) āĻĻুāϟা āĻŦৃāϤ্āϤাāĻ•াā§° āĻ•ুāĻŖ্āĻĄāϞী A āφ⧰ু B āχāϟোā§ąে āϏিāϟোā§° āĻ“āϚ⧰āϤ āĻŦāύ্āϧ āϕ⧰ি ā§°āĻ–া āĻšāϝ়। āϝāĻĻি āĻ•āχāϞ A āϤ āĻĨāĻ•া āĻ•াā§°েāĻŖ্āϟ āϏāϞāύি āϕ⧰া āĻšāϝ় āϤেāύ্āϤে āĻ•āχāϞ B āϤ āĻ•িāĻ›ু āĻ•াā§°েāĻŖ্āϟ āĻĒ্ā§°ā§°োāϚিāϤ āĻš’āĻŦāύে? āĻ•াā§°āĻŖ āĻĻিāϝ়āĻ•।

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15. State the rule to determine the direction of a (i) magnetic field produced around a straight conductor-carrying current, (ii) force experienced by a current-carrying straight conductor placed in a magnetic field which is perpendicular to it, and (iii) current induced in a coil due to its rotation in a magnetic field.

15. (i) āĻāϟা āĻĒোāύ āĻĒā§°িāĻŦাāĻšী āĻŦāĻšāύāĻ•াā§°ী āĻĒ্ā§°āĻŦাāĻšā§° āϚাā§°িāĻ“āĻĢাāϞে āĻ‰ā§ŽāĻĒāύ্āύ āĻšোā§ąা āϚুāĻŽ্āĻŦāĻ•ীāϝ় āĻ•্āώেāϤ্ā§°, (ii) āχāϝ়াā§° āϞāĻ—āϤ āϞāĻŽ্āĻŦāĻ­াā§ąে āĻĨāĻ•া āϚুāĻŽ্āĻŦāĻ•ীāϝ় āĻ•্āώেāϤ্ā§°āϤ āϏ্āĻĨাāĻĒāύ āϕ⧰া āĻĒ্ā§°āĻŦাāĻš āĻŦāĻšāύāĻ•াā§°ী āĻĒোāύ āĻĒā§°িāĻŦাāĻšীāϝ়ে āĻ…āύুāĻ­ā§ą āϕ⧰া āĻŦāϞ, āφ⧰ু ( iii) āϚুāĻŽ্āĻŦāĻ•ীāϝ় āĻ•্āώেāϤ্ā§°āϤ āϘূā§°্āĻŖāύ⧰ āĻĢāϞāϤ āĻ•ুāĻŖ্āĻĄāϞীāϤ āĻĒ্ā§°ā§°োāϚিāϤ āĻŦিāĻĻ্āϝুā§Ž āĻĒ্ā§°āĻŦাāĻš।

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16. Explain the underlying principle and working of an electric generator by drawing a labelled diagram. What is the function of brushes?

ā§§ā§Ŧ) āϞেāĻŦেāϞāϝুāĻ•্āϤ āĻĄাāϝ়েāĻ—্ā§°াāĻŽ āĻāĻ–āύ āφঁāĻ•ি āĻŦৈāĻĻ্āϝুāϤিāĻ• āϜেāύেā§°েāϟ⧰⧰ āĻ…āύ্āϤ⧰্āύিāĻšিāϤ āύীāϤি āφ⧰ু āĻ•াāĻŽ-āĻ•াāϜ⧰ āĻŦিāώāϝ়ে āĻŦ্āϝাāĻ–্āϝা āϕ⧰া। āĻŦ্ā§°াāϛ⧰ āĻ•াā§°্āϝ্āϝ āĻ•ি?

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17. When does an electric short circuit occur?

ā§§ā§­) āĻŦৈāĻĻ্āϝুāϤিāĻ• āĻļ্āĻŦā§°্āϟ āϚাā§°্āĻ•িāϟ āĻ•েāϤিāϝ়া āĻšāϝ়?

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18. What is the function of an earth wire? Why is it necessary to earth metallic appliances?

ā§§ā§Ž) āĻŽাāϟিā§° āϤাঁā§°ā§° āĻ•াā§°্āϝ্āϝ āĻ•ি? āϧাāϤুā§° āϏঁāϜুāϞিāĻŦোā§° āĻŽাāϟিāϤ āϞāĻ—াāĻŦ āϞাāĻ—ে āĻ•িāϝ়?

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