Chapter 12
āĻ āϧ্āϝাāϝ় ⧧⧍
Electricity
āĻŦিāĻĻ্āϝুā§
EXERCISES
āĻŦ্āϝাāϝ়াāĻŽ
ā§§) ā§°েāĻিāώ্āĻেāύ্āϏ R ā§° āϤাঁā§°ā§° āĻāĻা āĻুāĻুā§°া āϏāĻŽাāύ āĻĒাঁāĻāĻা āĻাāĻāϤ āĻাāĻি āĻĻিāϝ়া āĻšāϝ়। āϤাā§° āĻĒিāĻāϤ āĻāĻ āĻ ংāĻļāĻŦোā§° āϏāĻŽাāύ্āϤ⧰াāϞāĻাā§ąে āϏংāϝোāĻ āĻā§°া āĻšāϝ়। āϝāĻĻি āĻāĻ āϏংāĻŽিāĻļ্ā§°āĻŖā§° āϏāĻŽāϤুāϞ্āϝ ā§°েāĻিāώ্āĻেāύ্āϏ R' āĻšāϝ়, āϤেāύ্āϤে āĻ āύুāĻĒাāϤ R/R' āĻšāϝ়
2. Which of the following terms does not represent electrical power in a circuit?
⧍) āϤāϞ⧰ āĻোāύāĻো āĻļāĻŦ্āĻĻāĻ āĻŦā§°্āϤāύীāϤ āĻŦৈāĻĻ্āϝুāϤিāĻ āĻļāĻ্āϤিāĻ āĻĒ্ā§°āϤিāύিāϧিāϤ্āĻŦ āύāĻā§°ে?
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) āĻāĻা āĻāϞেāĻ্āĻ্ā§°িāĻ āĻŦাāϞ্āĻŦā§° ā§°েāĻিং ⧍⧍ā§Ļ āĻি āĻā§°ু ā§§ā§Ļā§Ļ ā§ąাāĻ āĻšāϝ়। āϝেāϤিāϝ়া āĻāϝ়াāĻ ā§§ā§§ā§Ļ āĻিāϤ āĻāϞোā§ąা āĻšāϝ়, āϤেāϤিāϝ়া āĻā§°āĻ āĻšোā§ąা āĻļāĻ্āϤি āĻš’āĻŦ -
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) āĻāĻেāĻা āĻĒāĻĻাā§°্āĻĨā§° āĻā§°ু āϏāĻŽাāύ āĻĻৈā§°্āĻ্āϝ āĻā§°ু āϏāĻŽাāύ āĻŦ্āϝাāϏ⧰ āĻĻুāĻা āĻĒā§°িāĻŦাāĻšী āϤাঁā§° āĻĒ্ā§°āĻĨāĻŽে āĻāĻেāĻা āĻŦিāĻā§ą āĻĒাā§°্āĻĨāĻ্āϝ⧰ āĻŽাāĻেā§°ে āĻāĻা āĻŦā§°্āϤāύীāϤ āϏāĻŽাāύ্āϤ⧰াāϞāĻাā§ąে āϏংāϝোāĻ āĻā§°া āĻšāϝ়। āĻļৃংāĻāϞা āĻā§°ু āϏāĻŽাāύ্āϤ⧰াāϞ āϏংāĻŽিāĻļ্ā§°āĻŖāϤ āĻā§āĻĒāύ্āύ āĻšোā§ąা āϤাāĻĒā§° āĻ āύুāĻĒাāϤ āĻš’āĻŦ -
5. How is a voltmeter connected in the circuit to measure the potential difference between two points? two points?
ā§Ģ) āĻĻুāĻা āĻŦিāύ্āĻĻুā§° āĻŽাāĻā§° āĻŦিāĻā§ąā§° āĻĒাā§°্āĻĨāĻ্āϝ āĻুāĻিāĻŦāϞৈ āĻŦā§°্āϤāύীāĻোāϤ āĻāĻা āĻāϞ্āĻāĻŽিāĻাā§° āĻেāύেāĻৈ āϏংāϝোāĻ āĻā§°া āĻšāϝ়? āĻĻুāĻা āĻĒāĻāĻŖ্āĻ?
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§° āĻāĻাā§° āĻŦ্āϝাāϏ ā§Ļ.ā§Ģ āĻŽিāϞিāĻŽিāĻাā§° āĻā§°ু āĻĒ্ā§°āϤিā§°োāϧ āĻ্āώāĻŽāϤা ā§§.ā§Ŧ x ā§§ā§Ļ-⧍ āĻŽিāĻাā§°। āĻāϝ়াā§° ā§°েāĻিāώ্āĻেāύ্āϏ ā§§ā§Ļ⧍ āĻŦāύাāĻŦāϞৈ āĻāĻ āϤাঁā§°āĻোā§° āĻĻৈā§°্āĻ্āϝ āĻিāĻŽাāύ āĻš’āĻŦ? āĻŦ্āϝাāϏ āĻĻুāĻুāĻŖ āĻā§°িāϞে ā§°েāĻিāώ্āĻেāύ্āϏ āĻিāĻŽাāύ 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§°েāĻিāώ্āĻā§°ā§° āĻāĻĒā§°েā§°ে āĻŦিāĻā§ą āĻĒাā§°্āĻĨāĻ্āϝ Vacross ā§° āϏংāĻļ্āϞিāώ্āĻ āĻŽাāύ⧰ āĻŦাāĻŦে āĻāĻা āύিā§°্āĻĻিāώ্āĻ ā§°েāĻিāώ্āĻā§°āϤ āĻĒ্ā§°āĻŦাāĻšিāϤ āĻাā§°েāĻŖ্āĻ I ā§° āĻŽাāύāϏāĻŽূāĻš āϤāϞāϤ āĻĻিāϝ়া āĻšৈāĻে
I (amperes) 0.5 1.0 2.0 3.0 4.0
I (āĻāĻŽ্āĻĒিāϝ়াā§°) ā§Ļ.ā§Ģ ā§§.ā§Ļ ⧍.ā§Ļ ā§Š.ā§Ļ ā§Ē.ā§Ļ
V (āĻāϞ্āĻ) ā§§.ā§Ŧ ā§Š.ā§Ē ā§Ŧ.ā§ ā§§ā§Ļ.⧍ ā§§ā§Š.⧍
V āĻā§°ু I ā§° āĻŽাāĻāϤ āĻāĻা āĻ্ā§°াāĻĢ āĻĒ্āϞāĻ āĻā§°āĻ āĻā§°ু āϏেāĻ ā§°েāĻিāώ্āĻā§°ā§° ā§°েāĻিāώ্āĻেāύ্āϏ āĻāĻŖāύা āĻā§°āĻ।
8. āϝেāϤিāϝ়া āĻāĻা 12 V āĻŦেāĻাā§°ী āĻāĻা āĻ āĻ্āĻাāϤ ā§°েāĻিāώ্āĻā§°ā§° āĻāĻĒā§°েā§°ে āϏংāϝোāĻ āĻā§°া āĻšāϝ়, āϤেāϤিāϝ়া āĻŦā§°্āϤāύীāĻোāϤ 2.5 mA āĻাā§°েāĻŖ্āĻ āĻĨাāĻে। ā§°েāĻিāώ্āĻā§°ā§° ā§°েāĻিāώ্āĻেāύ্āϏ⧰ āĻŽাāύ āĻŦিāĻাā§°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§° āĻāĻা āĻŦেāĻাā§°ী āĻ্ā§°āĻŽে 0.2,Ί, 0.3 Ί, 0.4 Ί, 0.5 Ί āĻā§°ু 12,Ί ā§°েāĻিāώ্āĻā§°ā§° āϏৈāϤে āĻļৃংāĻāϞাāĻŦāĻĻ্āϧāĻাā§ąে āϏংāϝোāĻ āĻā§°া āĻšāϝ়। 12 Ί ā§°েāĻিāώ্āĻā§°ā§° āĻŽাāĻেā§°ে āĻিāĻŽাāύ āĻাā§°েāĻŖ্āĻ āĻĒ্ā§°āĻŦাāĻšিāϤ āĻš’āĻŦ?
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 āϞাāĻāύāϤ 5 A āĻāĻĸ়িāϝ়াāĻ āύিāĻŦāϞৈ āĻিāĻŽাāύ 176 2 ā§°েāĻিāώ্āĻā§° (āϏāĻŽাāύ্āϤ⧰াāϞāĻাā§ąে)ā§° āĻĒ্ā§°āϝ়োāĻāύ? 11. āĻĻেāĻুā§ąাāĻāĻ āϝে āĻāĻĒুāύি āĻেāύেāĻৈ āϤিāύিāĻা ā§°েāĻিāώ্āĻā§° āϏংāϝোāĻ āĻā§°িāĻŦ, āĻĒ্ā§°āϤিāĻো ā§°েāĻিāώ্āĻেāύ্āϏ 62 ā§°, āϝাāϤে āϏংāĻŽিāĻļ্ā§°āĻŖā§° ā§°েāĻিāώ্āĻেāύ্āϏ (i) 9 2, (ii) 4 āĻšāϝ়।
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 āϝোāĻাāύ āϞাāĻāύāϤ āĻŦ্āĻ¯ā§ąāĻšাā§° āĻā§°িāĻŦāϞৈ āĻĄিāĻাāĻāύ āĻā§°া āĻেāĻāĻŦাāĻাāĻ āĻŦৈāĻĻ্āϝুāϤিāĻ āĻŦাāϞ্āĻŦā§°, 10 W ā§°েāĻিং āĻĻিāϝ়া āĻšৈāĻে। āϝāĻĻি āϏ⧰্āĻŦোāĻ্āĻ āĻ āύুāĻŽোāĻĻিāϤ āĻাā§°েāĻŖ্āĻ 5 A āĻšāϝ় āϤেāύ্āϤে 220 V āϞাāĻāύ⧰ āĻĻুāĻা āϤাঁā§°ā§° āĻāĻĒā§°েā§°ে āĻāĻোā§ąে āϏিāĻোā§° āϏāĻŽাāύ্āϤ⧰াāϞāĻাā§ąে āĻিāĻŽাāύāĻা āϞেāĻŽ্āĻĒ āϏংāϝোāĻ āĻā§°িāĻŦ āĻĒাā§°ি?
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 āϞাāĻāύ⧰ āϏৈāϤে āϏংāϝুāĻ্āϤ āĻŦৈāĻĻ্āϝুāϤিāĻ āĻ āĻেāύ⧰ āĻāĻা āĻšāĻ āĻĒ্āϞেāĻāϤ āĻĻুāĻা ā§°েāĻিāώ্āĻেāύ্āϏ āĻāĻāϞ A āĻā§°ু B āĻĨাāĻে, āĻĒ্ā§°āϤ্āϝেāĻā§°ে ⧍ā§Ē ā§°েāĻিāώ্āĻেāύ্āϏ āĻĨাāĻে, āϝিāĻŦোā§° āĻĒৃāĻĨāĻে āĻĒৃāĻĨāĻে, āĻļৃংāĻāϞাāĻŦāĻĻ্āϧāĻাā§ąে āĻŦা āϏāĻŽাāύ্āϤ⧰াāϞāĻাā§ąে āĻŦ্āĻ¯ā§ąāĻšাā§° āĻā§°িāĻŦ āĻĒাā§°ি। āϤিāύিāĻা āĻ্āώেāϤ্ā§°āϤ āĻি āĻি āĻাā§°েāĻŖ্āĻ āĻāĻে?
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§°āϤিāĻো āĻŦā§°্āϤāύীāϤ 2 ā§°েāĻিāώ্āĻā§°āϤ āĻŦ্āĻ¯ā§ąāĻšৃāϤ āĻļāĻ্āϤি āϤুāϞāύা āĻā§°āĻ: (1) 1 āĻā§°ু 2 ā§°েāĻিāώ্āĻā§°ā§° āϏৈāϤে āĻļৃংāĻāϞাāĻŦāĻĻ্āϧ āĻāĻা 6 V āĻŦেāĻাā§°ী, āĻā§°ু (ii) 12 āĻā§°ু 2 2 ā§°েāĻিāώ্āĻā§°ā§° āϏāĻŽাāύ্āϤ⧰াāϞāĻাā§ąে āĻāĻা 4 V āĻŦেāĻাā§°ী।
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) āĻĻুāĻা āϞেāĻŽ্āĻĒ, āĻāĻাā§° ā§°েāĻিং ⧍⧍ā§Ļ āĻিāϤ ā§§ā§Ļā§Ļ ā§ąাāĻ, āĻā§°ু āĻāύāĻো ⧍⧍ā§Ļ āĻিāϤ ā§Ŧā§Ļ ā§ąাāĻ, āĻŦৈāĻĻ্āϝুāϤিāĻ āĻŽেāĻāύ āĻাāĻĒ্āϞাāĻā§° āϏāĻŽাāύ্āϤ⧰াāϞāĻাā§ąে āϏংāϝোāĻ āĻā§°া āĻšāϝ়। āϝোāĻাāύ āĻāϞ্āĻেāĻ ā§¨ā§¨ā§Ļ āĻি āĻš’āϞে ā§°েāĻাāĻĄাāϞ⧰ āĻĒā§°া āĻি āĻাā§°েāĻŖ্āĻ āĻāϞিāĻā§ąা āĻšāϝ়?
16. Which uses more energy, a 250 W TV set in 1 hr, or a 1200 W toaster in 10 minutes?
ā§§ā§Ŧ) āĻোāύāĻোā§ąে āĻ āϧিāĻ āĻļāĻ্āϤি āĻŦ্āĻ¯ā§ąāĻšাā§° āĻā§°ে, ⧍ā§Ģā§Ļ ā§ąাāĻā§° āĻিāĻি āĻেāĻ ā§§ āĻāĻŖ্āĻাāϤ, āύে ⧧⧍ā§Ļā§Ļ ā§ąাāĻā§° āĻোāώ্āĻাā§° ā§§ā§Ļ āĻŽিāύিāĻāϤ?
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§°েāĻিāώ্āĻেāύ্āϏ 8 2 ā§° āĻāĻা āĻŦৈāĻĻ্āϝুāϤিāĻ āĻšিāĻাā§°ে āϏেā§ąাā§° āĻŽেāĻāύ⧰ āĻĒā§°া 2 āĻāĻŖ্āĻা 15 A āĻাāύি āĻāύে। āĻšিāĻাā§°āϤ āĻিāĻŽাāύ āĻšাā§°āϤ āϤাāĻĒ āĻŦিāĻāĻļিāϤ āĻšāϝ় āϏেāĻāĻো āĻāĻŖāύা āĻā§°া।
18. Explain the following.
ā§§ā§Ž) āϤāϞāϤ āĻĻিāϝ়া āĻāĻĨাāĻিāύি āĻŦুāĻাāĻ āĻĻিāϝ়া।
(āĻ) āĻাংāώ্āĻেāύ āĻĒ্ā§°াāϝ় āĻেā§ąāϞ āĻŦৈāĻĻ্āϝুāϤিāĻ āϞেāĻŽ্āĻĒā§° āĻĢিāϞাāĻŽেāĻŖ্āĻā§° āĻŦাāĻŦে āĻিāϝ় āĻŦ্āĻ¯ā§ąāĻšাā§° āĻā§°া āĻšāϝ়?
(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-āĻোāώ্āĻাā§° āĻā§°ু āĻŦৈāĻĻ্āϝুāϤিāĻ āϞোāĻšাā§° āĻĻā§°ে āĻŦৈāĻĻ্āϝুāϤিāĻ āĻāϤ্āϤাāĻĒāύ āϝāύ্āϤ্ā§°ā§° āĻĒā§°িāĻŦাāĻšীāĻŦোā§° āĻŦিāĻļুāĻĻ্āϧ āϧাāϤুā§° āĻĒā§°িā§ąā§°্āϤে āĻŽিāĻļ্ā§°āĻŖেā§°ে āĻিāϝ় āϤৈāϝ়াā§° āĻā§°া āĻšāϝ়?
(c) Why is the series arrangement not used for domestic circuits?
(āĻ) āĻā§°ুā§ąা āĻŦā§°্āϤāύীā§° āĻŦাāĻŦে āĻļৃংāĻāϞা āĻŦ্āĻ¯ā§ąāϏ্āĻĨাāĻো āĻিāϝ় āĻŦ্āĻ¯ā§ąāĻšাā§° āĻā§°া āύāĻšāϝ়?
(d) How does the resistance of a wire vary with its area of cross-section?
(āĻ) āϤাঁā§°ā§° āĻ্ā§°āĻ-āĻেāĻāĻāύ⧰ āĻ্āώেāϤ্ā§°āĻĢāϞ⧰ āϞāĻāϤ ā§°েāĻিāώ্āĻেāύ্āϏ āĻেāύেāĻৈ āϏāϞāύি āĻšāϝ়?
(e) Why are copper and aluminium wires usually employed for electricity transmission?
(āĻ) āĻŦিāĻĻ্āϝুā§ āϏāĻ্āĻাāϞāύ⧰ āĻŦাāĻŦে āϏাāϧাā§°āĻŖāϤে āϤাāĻŽ āĻā§°ু āĻāϞুāĻŽিāύিāϝ়াāĻŽā§° āϤাঁā§° āĻিāϝ় āĻŦ্āĻ¯ā§ąāĻšাā§° āĻā§°া āĻšāϝ়?