Chapter - 12

Electricity

( āĻŦিāĻĻ্āϝুā§Ž )


EXERCISES:-

( āĻŦ্āϝাāϝ়াāĻŽ:- )

1. A piece of wire of resistance R is cut into five equal parts. These parts are then connected in parallel. If the equivalent resistance of this combination is R, then the ratio R/R is -

( āĻĒ্ā§°āϤিā§°োāϧ āφ⧰-ā§° āϤাঁā§°ā§° āϟুāĻ•ুā§°া āĻāϟা āĻĒাঁāϚāϟা āϏāĻŽাāύ āĻ…ংāĻļāϤ āĻ•āϟা āĻšāϝ়। āĻāχ āĻ…ংāĻļāĻŦোā§° āϤাā§° āĻĒিāĻ›āϤ āϏāĻŽাāύ্āϤ⧰াāϞāĻ­াā§ąে āϏংāϝোāϜিāϤ āϕ⧰া āĻšāϝ়। āϝāĻĻি āĻāχ āĻŽিāĻļ্ā§°āĻŖāϟোā§° āϏāĻŽāϤুāϞ্āϝ āĻĒ্ā§°āϤিā§°োāϧ āĻšৈāĻ›ে āφ⧰, āϤেāύেāĻš'āϞে āφ⧰/āφ⧰ āĻ…āύুāĻĒাāϤ āĻšৈāĻ›ে - )

(a) 1/25 (b) 1/5 (c) 5 (d) 25

Answer:-

2. Which of the following terms does not represent electrical power in a circuit?

( āύিāĻŽ্āύāϞিāĻ–িāϤ āĻ•োāύāϟো āĻļāĻŦ্āĻĻāχ āĻŦā§°্āϤāύীāĻāϟাāϤ āĻŦৈāĻĻ্āϝুāϤিāĻ• āĻļāĻ•্āϤি āĻĒ্ā§°āϤিāύিāϧিāϤ্āĻŦ āύāϕ⧰ে? )

(a) FR (b) IR2 (c) VI (d) V/R

Answer:-

3. An electric bulb is rated 220 V and 100 W. When it is operated on 110 V, the power consumed will be

( āĻāϟা āĻŦৈāĻĻ্āϝুāϤিāĻ• āĻŦাāϞ্āĻŦāĻ• 220 āĻ­ি āφ⧰ু 100 āĻĄāĻŦ্āϞিāω ā§°েāϟিং āĻĻিāϝ়া āĻšāϝ়। āϝেāϤিāϝ়া āχāϝ়াāĻ• 110 āĻ­ি-āϤ āĻĒā§°িāϚাāϞāύা āϕ⧰া āĻšāϝ়, āĻŦ্āϝāϝ় āϕ⧰া āĻļāĻ•্āϤি āĻš'āĻŦ )

(a) 100 W

(b) 75 W

(c) 50 W

(d) 25 W

Answer:-

4. Two conducting wires of the same material and of equal lengths and equal diameters are first connected in series and then parallel in a circuit across the same potential difference. The ratio of heat produced in series and parallel combinations would be -

(āĻāĻ•ে āĻĒāĻĻাā§°্āĻĨā§° āĻĻুāϟা āĻĒā§°িāĻŦাāĻšী āϤাঁā§° āφ⧰ু āϏāĻŽাāύ āĻĻৈā§°্āϘ্āϝ āφ⧰ু āϏāĻŽাāύ āĻŦ্āϝাāϏ⧰ āĻĒ্ā§°āĻĨāĻŽে āĻļৃংāĻ–āϞাāϤ āϏংāϝোāϜিāϤ āĻšāϝ় āφ⧰ু āϤাā§° āĻĒিāĻ›āϤ āĻāĻ•ে āϏāĻŽ্āĻ­াā§ą্āϝ āĻĒাā§°্āĻĨāĻ•্āϝ⧰ āĻāϟা āĻŦā§°্āϤāύীāϤ āϏāĻŽাāύ্āϤ⧰াāϞāĻ­াā§ąে āϏংāϝোāϜিāϤ āϕ⧰া āĻšāϝ়। āĻļৃংāĻ–āϞা āφ⧰ু āϏāĻŽাāύ্āϤ⧰াāϞ āϏংāĻŽিāĻļ্ā§°āĻŖāϤ āĻ‰ā§ŽāĻĒাāĻĻিāϤ āϤাāĻĒā§° āĻ…āύুāĻĒাāϤ āĻš'āĻŦ - )

(a) 1:2

(b) 2:1

(c) 1:4

(d) 4:1

Answer:-

5. How is a voltmeter connected in the circuit to measure the potential difference between two points?

( āĻĻুāϟা āĻŦিāύ্āĻĻুā§° āĻŽাāϜ⧰ āϏāĻŽ্āĻ­াā§ą্āϝ āĻĒাā§°্āĻĨāĻ•্āϝ āϜোāĻ–াā§° āĻŦাāĻŦে āĻŦā§°্āϤāύীāϤ āĻāϟা āĻ­āϞ্āϟāĻŽিāϟাā§° āĻ•েāύেāĻĻā§°ে āϏংāϝোāϜিāϤ āĻšāϝ়? )

Answer:-

6. A copper wire has diameter 0.5 mm and resistivity of 1.6 x 10-82 m. What will be the length of this wire to make its resistance 10 2? How much does the resistance change if the diameter is doubled?

( āϤাāĻŽā§° āϤাঁā§°ā§° āĻŦ্āϝাāϏ ā§Ļ.ā§Ģ āĻŽিāĻŽি āφ⧰ু āĻĒ্ā§°āϤিā§°োāϧীāϤা ā§§.ā§Ŧ āĻāĻ•্āϏ ā§§ā§Ļ-ā§Žā§¨ āĻŽিāϟাā§°। āχāϝ়াā§° āĻĒ্ā§°āϤিā§°োāϧ ā§§ā§Ļ ⧍ āϕ⧰িāĻŦāϞৈ āĻāχ āϤাঁā§°ā§° āĻĻৈā§°্āϘ্āϝ āĻ•িāĻŽাāύ āĻš'āĻŦ? āϝāĻĻি āĻŦ্āϝাāϏ āĻĻুāĻ—ুāĻŖ āϕ⧰া āĻšāϝ় āϤেāύ্āϤে āĻĒ্ā§°āϤিā§°োāϧ āĻ•িāĻŽাāύ āĻĒā§°িā§ąā§°্āϤāύ āĻšāϝ়? )

Answer:-

7. The values of current I flowing in a given resistor for the corresponding values of potential difference Vacross the resistor are given below -

( āϏāĻŽ্āĻ­াā§ą্āϝ āĻĒাā§°্āĻĨāĻ•্āϝ⧰ āϏংāĻļ্āϞিāώ্āϟ āĻŽূāϞ্āϝāĻŦোā§°ā§° āĻŦাāĻŦে āĻŽāχ āĻĒ্ā§°āĻĻāϤ্āϤ ā§°েāϜিāώ্āϟ⧰āϤ āĻĒ্ā§°āĻŦাāĻšিāϤ āĻšোā§ąা āĻŦিāĻĻ্āϝুāϤ⧰ āĻŽূāϞ্āϝāĻŦোā§° āϤāϞāϤ āĻĻিāϝ়া āĻšৈāĻ›ে - )

I(amperes)   0.5  1.0  2.0  3.0  4.0

I(āĻāĻŽ্āĻĒিāϝ়াā§°) ā§Ļ.ā§Ģ ā§§.ā§Ļ ⧍.ā§Ļ ā§Š.ā§Ļ ā§Ē.ā§Ļ

V (volts) 1.6 3.4 6.7 10.2 13.2

V (āĻ­āϞ্āϟ) ā§§.ā§Ŧ ā§Š.ā§Ē ā§Ŧ.ā§­ ā§§ā§Ļ.⧍ ā§§ā§Š.⧍

Plot a graph between V and I and calculate the resistance of that resistor.

Answer:-

8. When a 12 V battery is connected across an unknown resistor, there is a current of 2.5 mA in the circuit. Find the value of the resistance of the resistor.

( āϝেāϤিāϝ়া āĻāϟা ⧧⧍ āĻ­ি āĻŦেāϟাā§°ী āĻ…āϜ্āĻžাāϤ ā§°েāϜিāώ্āϟ⧰⧰ āĻ“āĻĒā§°েā§°ে āϏংāϝোāϜিāϤ āĻšāϝ়, āĻŦā§°্āϤāύীāϟোāϤ ⧍.ā§Ģ āĻāĻŽāĻ āĻŦিāĻĻ্āϝুā§Ž āĻĨাāĻ•ে। āĻĒ্ā§°āϤিā§°োāϧāĻ•াā§°ীā§° āĻĒ্ā§°āϤিā§°োāϧ⧰ āĻŽূāϞ্āϝ āύিā§°্āĻŖāϝ় āϕ⧰āĻ•। )

Answer:-

9. A battery of 9 V is connected in series with resistors of 0.2 02, 0.3 0, 0.42, 0.52 and 12, respectively. How much current would flow through the 12 resistor?

( ⧝ āĻ­ি-ā§° āĻāϟা āĻŦেāϟাā§°ী āĻ•্ā§°āĻŽাāύ্āĻŦāϝ়ে ā§Ļ.⧍ ā§Ļ⧍, ā§Ļ.ā§Š ā§Ļ, ā§Ļ.ā§Ē⧍, ā§Ļ.ā§Ģ⧍ āφ⧰ু ⧧⧍ ā§° ā§°েāϜিāώ্āϟ⧰⧰ āϏৈāϤে āĻļৃংāĻ–āϞাāϤ āϏংāϝোāϜিāϤ āĻšāϝ়। ⧧⧍ ā§°েāϜিāώ্āϟ⧰⧰ āĻŽাāϜেā§°ে āĻ•িāĻŽাāύ āĻŦিāĻĻ্āϝুā§Ž āĻĒ্ā§°āĻŦাāĻšিāϤ āĻš'āĻŦ? )

Answer:-

10. How many 176 Q resistors (in parallel) are required to carry 5 A on a 220 V line?

( ⧍⧍ā§Ļ āĻ­ি āϞাāχāύāϤ ā§Ģ āĻ āĻ• āĻĸ়িāĻŦāϞৈ āĻ•িāĻŽাāύāϟা ā§§ā§­ā§Ŧ āĻ•িāω ā§°েāϜিāώ্āϟ⧰ (āϏāĻŽাāύ্āϤ⧰াāϞāĻ­াā§ąে) āĻĒ্ā§°āϝ়োāϜāύ? )

Answer:-

11. Show how you would connect three resistors, each of resistance 6 so that the combination has a resistance of (i) 9 , (ii) 4 .

( āφāĻĒুāύি āϤিāύিāϟা ā§°েāϜিāώ্āϟ⧰ āĻ•েāύেāĻĻā§°ে āϏংāϝোāĻ— āϕ⧰িāĻŦ āĻĻেāĻ–ুā§ąাāĻ“āĻ•, āĻĒ্ā§°āϤিāϟো āĻĒ্ā§°āϤিā§°োāϧ ā§Ŧ āϝাāϤে āĻŽিāĻļ্ā§°āĻŖāϟোāϤ (āĻ•) ⧝, (āφāχāφāχ) ā§Ē ā§° āĻĒ্ā§°āϤিā§°োāϧ āĻĨাāĻ•ে। )

Answer:-

12. Several electric bulbs designed to be used on a 220 V electric

( ⧍⧍ā§Ļ āĻ­ি āĻŦৈāĻĻ্āϝুāϤিāĻ• āϤ āĻŦ্āĻ¯ā§ąāĻšাā§° āϕ⧰িāĻŦāϞৈ āĻĄিāϜাāχāύ āϕ⧰া āĻ•েāχāĻŦাāϟাāĻ“ āĻŦৈāĻĻ্āϝুāϤিāĻ• āĻŦাāϞ্āĻŦ )

Answer:-

13. A hot plate of an electric oven connected to a 220 V line has two resistance coils A and B, each of 24 Ί resistance, which may be used separately, in series, or in parallel. What are the corrrents in the three case?

( ⧍⧍ā§Ļ āĻ­ি āϞাāχāύ⧰ āϏৈāϤে āϏংāϝোāϜিāϤ āĻŦৈāĻĻ্āϝুāϤিāĻ• āĻ…āĻ­েāύ⧰ āĻāϟা āĻ—ā§°āĻŽ āĻĒ্āϞেāϟāϤ āĻĻুāϟা āĻĒ্ā§°āϤিā§°োāϧ āĻ•ুāĻŖ্āĻĄāϞী āĻ āφ⧰ু āĻŦি āĻĨাāĻ•ে, āĻĒ্ā§°āϤিāϟোāϤ ⧍ā§Ē Ί āĻĒ্ā§°āϤিā§°োāϧ āĻĨাāĻ•ে, āϝাāĻ• āĻĒৃāĻĨāĻ•ে, āĻļৃংāĻ–āϞাāϤ āĻŦা āϏāĻŽাāύ্āϤ⧰াāϞāĻ­াā§ąে āĻŦ্āĻ¯ā§ąāĻšাā§° āϕ⧰া āĻš'āĻŦ āĻĒাā§°ে। āϤিāύিāϟা āĻ•্āώেāϤ্ā§°āϤ āĻ•ি āĻš'āĻŦ? )

Answer:-

14. Compare the power used in the 2 ÎŠ resistor in each of the following circuits: (i) a 6 V batter in series with 1 ÎŠ and 2 ÎŠ resistors, and (ii) a 4 V battery in parallel with 12 ÎŠ and 2 ÎŠ resistors.

( āύিāĻŽ্āύāϞিāĻ–িāϤ āĻĒ্ā§°āϤিāϟো āĻŦā§°্āϤāύীāϤ ⧍ Ί ā§°েāϜিāώ্āϟ⧰āϤ āĻŦ্āĻ¯ā§ąāĻšৃāϤ āĻļāĻ•্āϤি āϤুāϞāύা āϕ⧰āĻ•: (āφāχ) ā§§ Ί āφ⧰ু ⧍ Ί ā§°েāϜিāώ্āϟ⧰⧰ āϏৈāϤে āĻļৃংāĻ–āϞাāϤ ā§Ŧ āĻ­ি āĻŦেāϟাā§°, āφ⧰ু (āφāχāφāχ) ⧧⧍ Ί āφ⧰ু ⧍ Ί ā§°েāϜিāώ্āϟ⧰⧰ āϏāĻŽাāύ্āϤ⧰াāϞāĻ­াā§ąে ā§Ē āĻ­ি āĻŦেāϟাā§°ী। )

Answer:-

15. Two lamps, one rated 100 W at 220 V, and the other 60 W at 220 V, are connected in parallel to electric mains supply. What current is drawn from the line if the supply voltage is 220 V?

( āĻĻুāϟা āϞেāĻŽ্āĻĒ, āĻāϟা ⧍⧍ā§Ļ āĻ­ি-āϤ ā§§ā§Ļā§Ļ āĻĄāĻŦ্āϞিāω ā§°েāϟিং, āφ⧰ু āφāύāϟো ⧍⧍ā§Ļ āĻ­ি-āϤ ā§Ŧā§Ļ āĻĄāĻŦ্āϞিāω, āĻŦৈāĻĻ্āϝুāϤিāĻ• āĻŽেāχāύ āϝোāĻ—াāύ⧰ āϏāĻŽাāύ্āϤ⧰াāϞāĻ­াā§ąে āϏংāϝোāϜিāϤ। āϝāĻĻি āϝোāĻ—াāύ āĻ­āϞ্āϟেāϜ ⧍⧍ā§Ļ āĻ­ি āĻšāϝ় āϤেāύ্āϤে āϞাāχāύ⧰ āĻĒā§°া āĻ•ি āĻŦিāĻĻ্āϝুā§Ž āϏংāĻ—্ā§°āĻš āϕ⧰া āĻšāϝ়? )

Answer:-

 16. Which uses more energy, a 250 W TV set in 1 hr, or a 1200 W toaster in 10 minutes?

( āĻ•োāύে āĻ…āϧিāĻ• āĻļāĻ•্āϤি, 1 āϘāĻŖ্āϟাāϤ 250 āĻĄāĻŦ্āϞিāω āϟিāĻ­ি āĻ›েāϟ, āĻŦা 10 āĻŽিāύিāϟāϤ 1200 āĻĄāĻŦ্āϞিāω āϟোāώ্āϟাā§° āĻŦ্āĻ¯ā§ąāĻšাā§° āϕ⧰ে? )

Answer:-

17. An electric heater of resistance 8 2 draws 15 A from the service mains 2 hours. Calculate the rate at which heat is developed in the heater.

( āĻĒ্ā§°āϤিā§°োāϧ 8 2-ā§° āĻŦৈāĻĻ্āϝুāϤিāĻ• āĻšিāϟাā§°ে āϏেā§ąা ā§° āĻŽেāχāύ⧰ āĻĒā§°া 2 āϘāĻŖ্āϟা15 āĻ āϟা āϟাāύি āφāύে। āĻšিāϟাā§°āϤ āϤাāĻĒ āĻ•ি āĻšাā§°āϤ āĻŦিāĻ•āĻļিāϤ āĻšāϝ় āĻ—āĻŖāύা āϕ⧰āĻ•। )

Answer:-

18. Explain the following.

( āύিāĻŽ্āύāϞিāĻ–িāϤāĻŦোā§° āĻŦā§°্āĻŖāύা āϕ⧰āĻ•। )

(a) Why is the tungsten used almost exclusively for filament of electric lamps?

(āĻ•) āϟাংāώ্āϟেāύ āĻĒ্ā§°াāϝ় āĻ•েā§ąāϞ āĻŦৈāĻĻ্āϝুāϤিāĻ• āϞেāĻŽ্āĻĒā§° āĻĢিāϞাāĻŽেāĻŖ্āϟ⧰ āĻŦাāĻŦে āĻ•িāϝ় āĻŦ্āĻ¯ā§ąāĻšাā§° āϕ⧰া āĻšāϝ়?

Answer:-

(b) Why are the conductors of electric heating devices, such as bread-toasters and electric irons, made of an alloy rather than a pure metal?

(āĻ–) āĻŦ্ā§°েāĻĄ-āϟোāώ্āϟাā§° āφ⧰ু āĻŦৈāĻĻ্āϝুāϤিāĻ• āϞোāĻšাā§° āĻĻā§°ে āĻŦৈāĻĻ্āϝুāϤিāĻ• āωāϤ্āϤাāĻĒāύ āϝāύ্āϤ্ā§°ā§° āĻĒā§°িāĻŦাāĻšীāĻŦোā§° āĻŦিāĻļুāĻĻ্āϧ āϧাāϤুā§° āĻĒā§°িā§ąā§°্āϤে āĻŽিāĻļ্ā§°āĻŖেā§°ে āĻ•িāϝ় āϤৈāϝ়াā§° āϕ⧰া āĻšāϝ়?

Answer:-

(Ⓒ) Why is the series arrangement not used for domestic circuits?

(Ⓒ) āϘ⧰ুā§ąা āĻŦā§°্āϤāύীā§° āĻŦাāĻŦে āĻļৃংāĻ–āϞা āĻŦ্āĻ¯ā§ąāϏ্āĻĨাāϟো āĻ•িāϝ় āĻŦ্āĻ¯ā§ąāĻšাā§° āϕ⧰া āύāĻšāϝ়?

Answer:-

(d) How does the resistance of a wire vary with its area of cross-section?

(āϘ) āϤাঁā§°ā§° āĻ•্ā§°āĻ›-āĻ›েāĻ•āϚāύ⧰ āĻ•্āώেāϤ্ā§°āĻĢāϞ⧰ āϞāĻ—āϤ ā§°েāϜিāώ্āϟেāύ্āϏ āĻ•েāύেāĻ•ৈ āϏāϞāύি āĻšāϝ়?

Answer:-

(e) Why are copper and aluminium wires usually employed for electricity transmission?

(āĻ™) āĻŦিāĻĻ্āϝুā§Ž āϏāĻž্āϚাāϞāύ⧰ āĻŦাāĻŦে āϏাāϧাā§°āĻŖāϤে āϤাāĻŽ āφ⧰ু āĻāϞুāĻŽিāύিāϝ়াāĻŽā§° āϤাঁā§° āĻ•িāϝ় āĻŦ্āĻ¯ā§ąāĻšাā§° āϕ⧰া āĻšāϝ়?

Answer:-



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