Chapter 12

āĻ…āϧ্āϝাāϝ় ⧧⧍

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

ā§§) ā§°েāϜিāώ্āϟেāύ্āϏ R ā§° āϤাঁā§°ā§° āĻāϟা āϟুāĻ•ুā§°া āϏāĻŽাāύ āĻĒাঁāϚāϟা āĻ­াāĻ—āϤ āĻ•াāϟি āĻĻিāϝ়া āĻšāϝ়। āϤাā§° āĻĒিāĻ›āϤ āĻāχ āĻ…ংāĻļāĻŦোā§° āϏāĻŽাāύ্āϤ⧰াāϞāĻ­াā§ąে āϏংāϝোāĻ— āϕ⧰া āĻšāϝ়। āϝāĻĻি āĻāχ āϏংāĻŽিāĻļ্ā§°āĻŖā§° āϏāĻŽāϤুāϞ্āϝ ā§°েāϜিāώ্āϟেāύ্āϏ R' āĻšāϝ়, āϤেāύ্āϤে āĻ…āύুāĻĒাāϤ R/R' āĻšāϝ়

 (a) 1/25  (ā§§/⧍ā§Ģ)

 (b) 1/5   (ā§§/ā§Ģ)

 (c) 5    (ā§Ģ)

 (d) 25    (⧍ā§Ģ)

Ans-


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

⧍) āϤāϞ⧰ āĻ•োāύāϟো āĻļāĻŦ্āĻĻāχ āĻŦā§°্āϤāύীāϤ āĻŦৈāĻĻ্āϝুāϤিāĻ• āĻļāĻ•্āϤিāĻ• āĻĒ্ā§°āϤিāύিāϧিāϤ্āĻŦ āύāϕ⧰ে?

 (a) FR

 (b) IR2

 (c) VI

 (d) v2/R

 Ans-


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

ā§Š) āĻāϟা āχāϞেāĻ•্āϟ্ā§°িāĻ• āĻŦাāϞ্āĻŦā§° ā§°েāϟিং ⧍⧍ā§Ļ āĻ­ি āφ⧰ু ā§§ā§Ļā§Ļ ā§ąাāϟ āĻšāϝ়। āϝেāϤিāϝ়া āχāϝ়াāĻ• ā§§ā§§ā§Ļ āĻ­িāϤ āϚāϞোā§ąা āĻšāϝ়, āϤেāϤিāϝ়া āĻ–ā§°āϚ āĻšোā§ąা āĻļāĻ•্āϤি āĻš’āĻŦ -

 (a) 100 W   

 (b) 75 W    

 (c) 50 W.

 (d) 25 W

 Ans-


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 -

ā§Ē) āĻāĻ•েāϟা āĻĒāĻĻাā§°্āĻĨā§° āφ⧰ু āϏāĻŽাāύ āĻĻৈā§°্āϘ্āϝ āφ⧰ু āϏāĻŽাāύ āĻŦ্āϝাāϏ⧰ āĻĻুāϟা āĻĒā§°িāĻŦাāĻšী āϤাঁā§° āĻĒ্ā§°āĻĨāĻŽে āĻāĻ•েāϟা āĻŦিāĻ­ā§ą āĻĒাā§°্āĻĨāĻ•্āϝ⧰ āĻŽাāϜেā§°ে āĻāϟা āĻŦā§°্āϤāύীāϤ āϏāĻŽাāύ্āϤ⧰াāϞāĻ­াā§ąে āϏংāϝোāĻ— āϕ⧰া āĻšāϝ়। āĻļৃংāĻ–āϞা āφ⧰ু āϏāĻŽাāύ্āϤ⧰াāϞ āϏংāĻŽিāĻļ্ā§°āĻŖāϤ āĻ‰ā§ŽāĻĒāύ্āύ āĻšোā§ąা āϤাāĻĒā§° āĻ…āύুāĻĒাāϤ āĻš’āĻŦ -

 (a) 1:2

 (b) 2:1

 (c) 1:4

 Ans-


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

ā§Ģ) āĻĻুāϟা āĻŦিāύ্āĻĻুā§° āĻŽাāϜ⧰ āĻŦিāĻ­ā§ąā§° āĻĒাā§°্āĻĨāĻ•্āϝ āϜুāĻ–িāĻŦāϞৈ āĻŦā§°্āϤāύীāϟোāϤ āĻāϟা āĻ­āϞ্āϟāĻŽিāϟাā§° āĻ•েāύেāĻ•ৈ āϏংāϝোāĻ— āϕ⧰া āĻšāϝ়? āĻĻুāϟা āĻĒāχāĻŖ্āϟ?

Ans-


6. A copper wire has diameter 0.5 mm and resistivity of 1.6 x 10-2 m. What will be the length of this wire to make its resistance 102? How much does the resistance change if the diameter is doubled?

ā§Ŧ) āϤাāĻŽā§° āϤাঁā§° āĻāϟাā§° āĻŦ্āϝাāϏ ā§Ļ.ā§Ģ āĻŽিāϞিāĻŽিāϟাā§° āφ⧰ু āĻĒ্ā§°āϤিā§°োāϧ āĻ•্āώāĻŽāϤা ā§§.ā§Ŧ x ā§§ā§Ļ-⧍ āĻŽিāϟাā§°। āχāϝ়াā§° ā§°েāϜিāώ্āϟেāύ্āϏ ā§§ā§Ļ⧍ āĻŦāύাāĻŦāϞৈ āĻāχ āϤাঁā§°āϟোā§° āĻĻৈā§°্āϘ্āϝ āĻ•িāĻŽাāύ āĻš’āĻŦ? āĻŦ্āϝাāϏ āĻĻুāĻ—ুāĻŖ āϕ⧰িāϞে ā§°েāϜিāώ্āϟেāύ্āϏ āĻ•িāĻŽাāύ āϏāϞāύি āĻšāϝ়?

Ans-


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

7. ā§°েāϜিāώ্āϟ⧰⧰ āĻ“āĻĒā§°েā§°ে āĻŦিāĻ­ā§ą āĻĒাā§°্āĻĨāĻ•্āϝ Vacross ā§° āϏংāĻļ্āϞিāώ্āϟ āĻŽাāύ⧰ āĻŦাāĻŦে āĻāϟা āύিā§°্āĻĻিāώ্āϟ ā§°েāϜিāώ্āϟ⧰āϤ āĻĒ্ā§°āĻŦাāĻšিāϤ āĻ•াā§°েāĻŖ্āϟ I ā§° āĻŽাāύāϏāĻŽূāĻš 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§¨.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.⧍

Ans-


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

V āφ⧰ু I ā§° āĻŽাāϜāϤ āĻāϟা āĻ—্ā§°াāĻĢ āĻĒ্āϞāϟ āϕ⧰āĻ• āφ⧰ু āϏেāχ ā§°েāϜিāώ্āϟ⧰⧰ ā§°েāϜিāώ্āϟেāύ্āϏ āĻ—āĻŖāύা āϕ⧰āĻ•।

 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.

8. āϝেāϤিāϝ়া āĻāϟা 12 V āĻŦেāϟাā§°ী āĻāϟা āĻ…āϜ্āĻžাāϤ ā§°েāϜিāώ্āϟ⧰⧰ āĻ“āĻĒā§°েā§°ে āϏংāϝোāĻ— āϕ⧰া āĻšāϝ়, āϤেāϤিāϝ়া āĻŦā§°্āϤāύীāϟোāϤ 2.5 mA āĻ•াā§°েāĻŖ্āϟ āĻĨাāĻ•ে। ā§°েāϜিāώ্āϟ⧰⧰ ā§°েāϜিāώ্āϟেāύ্āϏ⧰ āĻŽাāύ āĻŦিāϚাā§°āĻ•।

Ans-


9. A battery of 9 V is connected in series with resistors of 0.2,Ί, 0.3 Ί, 0.4 Ί, 0.5 Ί and 12,Ί respectively. How much current would flow through the 12 Ί resistor?

9. 9 V ā§° āĻāϟা āĻŦেāϟাā§°ী āĻ•্ā§°āĻŽে 0.2,Ί, 0.3 Ί, 0.4 Ί, 0.5 Ί āφ⧰ু 12,Ί ā§°েāϜিāώ্āϟ⧰⧰ āϏৈāϤে āĻļৃংāĻ–āϞাāĻŦāĻĻ্āϧāĻ­াā§ąে āϏংāϝোāĻ— āϕ⧰া āĻšāϝ়। 12 Ί ā§°েāϜিāώ্āϟ⧰⧰ āĻŽাāϜেā§°ে āĻ•িāĻŽাāύ āĻ•াā§°েāĻŖ্āϟ āĻĒ্ā§°āĻŦাāĻšিāϤ āĻš’āĻŦ?

 Ans-


10. How many 176 2 resistors (in parallel) are required to carry 5 A on a 220 V line? 11. Show how you would connect three resistors, each of resistance 62, so that the combination has a resistance of (i) 9 2, (ii) 4.

10. 220 V āϞাāχāύāϤ 5 A āĻ•āĻĸ়িāϝ়াāχ āύিāĻŦāϞৈ āĻ•িāĻŽাāύ 176 2 ā§°েāϜিāώ্āϟ⧰ (āϏāĻŽাāύ্āϤ⧰াāϞāĻ­াā§ąে)ā§° āĻĒ্ā§°āϝ়োāϜāύ? 11. āĻĻেāĻ–ুā§ąাāĻ“āĻ• āϝে āφāĻĒুāύি āĻ•েāύেāĻ•ৈ āϤিāύিāϟা ā§°েāϜিāώ্āϟ⧰ āϏংāϝোāĻ— āϕ⧰িāĻŦ, āĻĒ্ā§°āϤিāϟো ā§°েāϜিāώ্āϟেāύ্āϏ 62 ā§°, āϝাāϤে āϏংāĻŽিāĻļ্ā§°āĻŖā§° ā§°েāϜিāώ্āϟেāύ্āϏ (i) 9 2, (ii) 4 āĻšāϝ়।

 Ans-


12. Several electric bulbs designed to be used on a 220 V electric supply line, are rated 10 W. How many lamps can be connected in parallel with each other across the two wires of 220 V line if the maximum allowable current is 5 A?

12. 220 V āĻŦৈāĻĻ্āϝুāϤিāĻ• āϝোāĻ—াāύ āϞাāχāύāϤ āĻŦ্āĻ¯ā§ąāĻšাā§° āϕ⧰িāĻŦāϞৈ āĻĄিāϜাāχāύ āϕ⧰া āĻ•েāχāĻŦাāϟাāĻ“ āĻŦৈāĻĻ্āϝুāϤিāĻ• āĻŦাāϞ্āĻŦā§°, 10 W ā§°েāϟিং āĻĻিāϝ়া āĻšৈāĻ›ে। āϝāĻĻি āϏ⧰্āĻŦোāϚ্āϚ āĻ…āύুāĻŽোāĻĻিāϤ āĻ•াā§°েāĻŖ্āϟ 5 A āĻšāϝ় āϤেāύ্āϤে 220 V āϞাāχāύ⧰ āĻĻুāϟা āϤাঁā§°ā§° āĻ“āĻĒā§°েā§°ে āχāϟোā§ąে āϏিāϟোā§° āϏāĻŽাāύ্āϤ⧰াāϞāĻ­াā§ąে āĻ•িāĻŽাāύāϟা āϞেāĻŽ্āĻĒ āϏংāϝোāĻ— āϕ⧰িāĻŦ āĻĒাā§°ি?

 Ans-


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

ā§§ā§Š) ⧍⧍ā§Ļ āĻ­ি āϞাāχāύ⧰ āϏৈāϤে āϏংāϝুāĻ•্āϤ āĻŦৈāĻĻ্āϝুāϤিāĻ• āĻ…āĻ­েāύ⧰ āĻāϟা āĻšāϟ āĻĒ্āϞেāϟāϤ āĻĻুāϟা ā§°েāϜিāώ্āϟেāύ্āϏ āĻ•āχāϞ A āφ⧰ু B āĻĨাāĻ•ে, āĻĒ্ā§°āϤ্āϝেāϕ⧰ে ⧍ā§Ē ā§°েāϜিāώ্āϟেāύ্āϏ āĻĨাāĻ•ে, āϝিāĻŦোā§° āĻĒৃāĻĨāĻ•ে āĻĒৃāĻĨāĻ•ে, āĻļৃংāĻ–āϞাāĻŦāĻĻ্āϧāĻ­াā§ąে āĻŦা āϏāĻŽাāύ্āϤ⧰াāϞāĻ­াā§ąে āĻŦ্āĻ¯ā§ąāĻšাā§° āϕ⧰িāĻŦ āĻĒাā§°ি। āϤিāύিāϟা āĻ•্āώেāϤ্ā§°āϤ āĻ•ি āĻ•ি āĻ•াā§°েāĻŖ্āϟ āφāĻ›ে?

 Ans-


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

14. āϤāϞāϤ āĻĻিāϝ়া āĻĒ্ā§°āϤিāϟো āĻŦā§°্āϤāύীāϤ 2 ā§°েāϜিāώ্āϟ⧰āϤ āĻŦ্āĻ¯ā§ąāĻšৃāϤ āĻļāĻ•্āϤি āϤুāϞāύা āϕ⧰āĻ•: (1) 1 āφ⧰ু 2 ā§°েāϜিāώ্āϟ⧰⧰ āϏৈāϤে āĻļৃংāĻ–āϞাāĻŦāĻĻ্āϧ āĻāϟা 6 V āĻŦেāϟাā§°ী, āφ⧰ু (ii) 12 āφ⧰ু 2 2 ā§°েāϜিāώ্āϟ⧰⧰ āϏāĻŽাāύ্āϤ⧰াāϞāĻ­াā§ąে āĻāϟা 4 V āĻŦেāϟাā§°ী।

 Ans-


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?

ā§§ā§Ģ) āĻĻুāϟা āϞেāĻŽ্āĻĒ, āĻāϟাā§° ā§°েāϟিং ⧍⧍ā§Ļ āĻ­িāϤ ā§§ā§Ļā§Ļ ā§ąাāϟ, āφ⧰ু āφāύāϟো ⧍⧍ā§Ļ āĻ­িāϤ ā§Ŧā§Ļ ā§ąাāϟ, āĻŦৈāĻĻ্āϝুāϤিāĻ• āĻŽেāχāύ āϚাāĻĒ্āϞাāχ⧰ āϏāĻŽাāύ্āϤ⧰াāϞāĻ­াā§ąে āϏংāϝোāĻ— āϕ⧰া āĻšāϝ়। āϝোāĻ—াāύ āĻ­āϞ্āϟেāϜ ⧍⧍ā§Ļ āĻ­ি āĻš’āϞে ā§°েāĻ–াāĻĄাāϞ⧰ āĻĒā§°া āĻ•ি āĻ•াā§°েāĻŖ্āϟ āωāϞিāĻ“ā§ąা āĻšāϝ়?

 Ans-


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

ā§§ā§Ŧ) āĻ•োāύāϟোā§ąে āĻ…āϧিāĻ• āĻļāĻ•্āϤি āĻŦ্āĻ¯ā§ąāĻšাā§° āϕ⧰ে, ⧍ā§Ģā§Ļ ā§ąাāϟ⧰ āϟিāĻ­ি āϚেāϟ ā§§ āϘāĻŖ্āϟাāϤ, āύে ⧧⧍ā§Ļā§Ļ ā§ąাāϟ⧰ āϟোāώ্āϟাā§° ā§§ā§Ļ āĻŽিāύিāϟāϤ?

 Ans-


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.

17. ā§°েāϜিāώ্āϟেāύ্āϏ 8 2 ā§° āĻāϟা āĻŦৈāĻĻ্āϝুāϤিāĻ• āĻšিāϟাā§°ে āϏেā§ąাā§° āĻŽেāχāύ⧰ āĻĒā§°া 2 āϘāĻŖ্āϟা 15 A āϟাāύি āφāύে। āĻšিāϟাā§°āϤ āĻ•িāĻŽাāύ āĻšাā§°āϤ āϤাāĻĒ āĻŦিāĻ•āĻļিāϤ āĻšāϝ় āϏেāχāϟো āĻ—āĻŖāύা āϕ⧰া।

 Ans-


18. Explain the following.

ā§§ā§Ž) āϤāϞāϤ āĻĻিāϝ়া āĻ•āĻĨাāĻ–িāύি āĻŦুāϜাāχ āĻĻিāϝ়া।

 (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?

 Ans-

(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?

 Ans-


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

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

 Ans-


(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?

 Ans-


(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?

 Ans-