Current objective assignment – (1)

## Electric conduction ohm’s law and resistance.

**Answers of all the questions are given at the end of all questions of the assignment.**

1. for which if the following depends of drift velocity v on electric field E is Ohm’s law obeyed ? (a) v α E (b) v= constant (c) v α E ^{½ } (d) v α E ^{2} .

2. A potential difference is applied across the end of the metallic wire . If the potential difference is doubled , the drift velocity ; (a) will be doubled, (b) will be halved, (c) will be quadrupled, (d) no change .

3. The maximum current that flows in the fuse wire , before it blows out , varies with the radius r as :(a) r^{3/2} (b) r (c) r^{2/3} (d) r ^{½}

4. The mass of three wires of copper are in the ratio of 1:3:5 and their length are in the ratio 5:3:1 . T he ratio of their electric resistance is ; (a) 1:3:5 (b) 5:3:1 (c) 1:15:125 (d) 125:15:1

5. The temperature (T) dependence of resistivity of a semiconductor represented by :

6. A wire of resistance R b= is stretched till its radius is half of its original value . Then the radius of the stretched wire is ; (a) 2R (b) 4R (c) 8R (d) 16R :

7. A wire till its length is doubled of its original length , then the resistance of the stretched wire is; (a) 2R (b) 4R (c) 8R (d) 16R :

8. If a copper wire is stretched to make it 0.1% longer, then the percentage change in its resistance is approximately (a) 0.1% (b) 0.2 % (c) 0.4% (d) 0.8% .

9. If a copper wire is stretched to make its radius decrease by 0.1% , then the % change in its resistance is approximately ; (a) 0.1% (b) 0.2 % (c) 0.4% (d) 0.8% .

10. A current of 5 amp exist in the 10 ohm resistance, for 4 minutes . How many coulombs pass through any cross-section of the resistor in this time ? (a) 12 (b) 120 (c) 1200 (d) 12000.

11. The temperature coefficient of resistance of a wire is 0.00125/^{0}C at 300K is one Ohm. The resistance of the wire will be 2 ohm at (a)1154K (b) 1100k (c) 1400k (d) 1127k .

12. Drift speed of electrons is of the order of ; (a) zero (b) 10^{-2} (c) 10^{5} (d) 10^{0}m/s ;

13. Which represents the negative dynamic resistance?

(a) AB (b) BC (c)CD (d) DA

14. When a current flows in a wire , there exist in electric field in the direction of ; (a) flow of current, (b) opposite to the flow of current (c) perpendicular to the flow of current (d)at the angle of 45^{0} to the flow of current.

15. The drift velocity of free electron in a conductor is v when a current I is flow in it . If both the radius and current are doubled , then drift velocity will be; (a) v (b) v/2 (c) v/4 (d) v/8 .

16. The sides of rectangular block are 2,3 and 4cm . the ratio of maximum to minimum resistance between its parallel face is; (a) 4 (b)3 (c) 2 (d) 1 ;

17. The electric resistance of certain wire is R, if its length and radius both are doubled , then ; (a) resistance will be doubled and the specific resistance will be halved (b) resistance will be halved and the specific resistance will be remain same (c) resistance will be halved and the specific resistance will be doubled (d) resistance will be unchanged and also the specific resistance will be unchanged.

18. Total no. of electrons present in 4 amp current flowing for 1 sec is ; (a) 2.5 x 10^{9} (b)2.5x 10^{20} (c) 1.25×10^{13} (d) 6x 10^{8} .

19. If the electric current through a bulb is 3.2 A, the no of electrons flowing through it in 1 sec is; (a) 2 x 10^{9} (b) 2 x 10^{19} (c) 3.2 x 10^{9} (d) 1.6 x 10^{18} .

20. The resistance of a wire is 5 ohm at 50^{0}c and 6 ohm at 100^{0}c , the resistance of the wire at 0^{0}c will be; (a) 3 ohm (b) 2 ohm (c) 1 ohm (d) 4 ohm .

21. Two wires have length ,diameter and resistivity all are in the ratio 1:2 the resistance of the first wire is 10 ohm, the resistance of the second wire is ; (a) 5 (b) 10 (c) 20 (d) infinity.

22. Two copper wire have their masses in the ratio 2:3 and the length in the ratio 3:4 , the ratio of their resistance is ; (a) 4:9 (b) 27:32 (c) 16:9 (d) 27:128 (e) 1:2 ,

23.On increasing the temperature of the conductor its resistance increases because the ; (a) relaxation time increases (b) mass of electron increases (c) electron density decreases (d) relaxation time decreases .

24 .The resistance of a wire is R ohm . It is melted and stretched to n times its original length , the new resistance will be ; (a) R/n (b) n^{2}R (c)R/ n^{2} (d) nR .

25. The current flowing through a wire depends on time as I = 3t^{2} +2t +5 . The charge flowing through the cross-section of the wire in time from t=0 to t=2 sec is; (a) 22c (b) 20c (c) 18c (d) 5c.

ans- Ans- 1-a ;2- a ; 3-a ;4- d ;5-b ;6-d ; 7-b ; 8-b ; 9-c ;10-c ; 11-d; 12- b ; 13 -c; 14-a ;15-b ;16- a; 17-b ; 18-a ; 19-b ; 20-d ; 21-b ; 22-b ; 23-d ;24-b ;25-a