55886aa

8/10/2019 55886aa

1/14

Current Electricity

Copyright Ace Creative Learning Pvt Ltd.,|| www.ace-online.co.in

ARevision Material

Homework Questions

1. A copper wire of length 60 cm and cross sectional area 7 210 m carries a current of 1.6A . How long

will an electron take to drift from one end of the wire to the another. Assume that there are 2910 free

electrons per

3min copper.

(a) 610 sec (b) 1010 sec (c) 10 min (d) 2 min

Sol: 3 129 19 7

1.610 ms

10 1.6 10 10d

iv

neA

3

0.6600 10

10d

Lt s

v min

Ans: (c)

2. A wire is stretched to make it 0.1% longer. What is the percentage change in resistance?

(a) 0.1% (b) 0.2% (c) 0.3% (d) 0.4%

Sol:2

RA V

2R r 100 2 100

R

R

2 0.1% 0.2% .

Ans: (b)

3. Find the value of current I in the circuit shown

(a) 1 A (b) 2 A

(c)

3 A (d) 4 A

Sol: Applying KVL

0 4 3 9 2 0 0i i i

9 9 1i i A

Ans: (a)

3 9 V

2

DA

BC

4

8/10/2019 55886aa

2/14

Current Electricity


ARevision Material

4. An electric cable having a resistance of 0.2 delivers 10 kWof power at 200 V to a factory. Find the

efficiency of transmission.

(a) 43.5% (b) 50% (c) 83.5% (d) 95%

Sol: 0.2R , 10 kWP , 200 VV

Power loss in the cable2

2 pI R RV

23

10 10 2 100 100 20.5 kW

200 10 4 10

Total power supported by the source 10 0.5 10.5 kW

power delivered 10= 0.95 95%

powersupplied 10.5

Ans: (d)5. For the given circuit the potential difference between the points x and y is

(a) 3.2 A

(b)4.8 A

(c) 5.6 A (d) 6.2 A

Sol: Current in the circuit

6 4 1

8 2 5i A

2 6 0y xV i V

12 6 2 6

5y xV V i

2 30

5.6 A5

Ans: (c)

6. The deflection in . .M C G falls from 50 to 10 division when a shunt of 12 is connected across it. The

resistance of the galvanometer coil is.

(a) 12 (b) 24 (c) 36 (d) 48

6 V6 V

4 V8

iyx

4 ,8V

X y

6 , 2V

8/10/2019 55886aa

3/14

Current Electricity


ARevision Material

Sol:

50 KI , 1 10 KgI

' 'g gI G I I S

1 Sg

IG

I

501 12 4 12 48

10

Ans: (d)

7. The current in the circuit shown is

(a)

0.1 A (b) 0.2 A

(c) 0.3 A (d) 0.4 A

Sol:

The effective resistance

60 3020

60 30R

20.1

20

Vi A

R

Ans: (a)

8. A battery of emf E and internal resistance ' 'r is connected across a pure resistors of resistance R .

The power output of the device is maximum if

(a) r R (b) 2r R

(c) 2r R (d) r R

G

'gI I

S

G

'gI

'gI I

30

30 30

2V

2V

30

30 30

8/10/2019 55886aa

4/14

Current Electricity


ARevision Material

Sol: Current in the circuitE

ir R

power output2

R Ep i Rr R

maxi is possible if 0dpdR

and2

2

d po

dR

2

2 0

dp E R r

dR R r R r

R r and also2

20

d p

dR

Ans: (a)

9. A set of ' 'n identical resistors each of resistance ' 'R ohm when connected in series has an effective

resistance ' 'x ohm. When the resistance is ' 'y ohm, what is the relation between ,R x and y ?

(a)xy

Rx y

(b) R y x (c)R xy (d)1

Rxy

Sol: When in series nR x (1)

When in parallelR

yn (2)

From (1) and (2) RnR xyn

2R xy , R xy

Ans: (c)

10. For the circuit shown, the current through the galvanometer will be zero if the value of resistance ' 'x is

(a) 4 (b) 6 (c) 12 (d) 24

rE

i

R

2 3 4

12

10

x

G

V

8/10/2019 55886aa

5/14

Current Electricity


ARevision Material

Sol: 5P , 4Q , 10R ,12

12

xS

x

P R

Q S

5 10 124 12

xx

3 24 2x x

24x

Ans: (d)

11. Find the value of current I in the circuit shown

(a) 1 A (b) 2 A

(c) 3 A (d) 4 A

Sol: Applying KVL:

2 9 3 4 0D AV i i i V

9 d Aqi V V

1i A 0 0qi q

Ans: (a)

12. Two Resistors of 400 and 600 are connected in series with a

5.0 V battery of negligible internal resistance. A voltmeter of

resistance 9600 is used to measure the potential difference across

the 400 resistor. Find the error in the measurement of potential

difference.

(a) 0.05 V (b) 0.5 V

(c) 5 V (d) 5 V

3

4 2

B

A D

CI

9V

9600

400 600

5.0V

3

4 2

I

9V

8/10/2019 55886aa

6/14

Current Electricity


ARevision Material

Sol: Total resistance of the circuit

1 400 9600600 984

400 9600R

Total current in the circuit5

' A

984

I

Potential difference measured by voltmeter5

384 1.95V984

Actual potential difference across 400 resistor is5

400 2V400 600

V

Error 2 1.95 0.05 V

Ans: (a)

13. A 100W,250V bulb 1B and two 60W, 250V bulbs 2B and 3B are connected to 250 V source as

shown. If 1 2,W W and 3W are output powers of the bulbs 1 2,B B and 3B respectively. Then

(a) 1 2 3W W W (b) 1 2 3W W W

(c) 1 2 3W W W (d) 1 2 3W W W

Sol:

The resistance of bulbs 1 2 3, ,B B B are

2

11

250 250625100

VR P

2

3 22

250 250 2501042

60R R

P

Voltage across 1B is 1V1

1 2

250 62593.7 V

625 1024

VR

R R

250V

3B

1B 2B

1R 2R

3R

250V

8/10/2019 55886aa

7/14

Current Electricity


ARevision Material

Voltage across 2B is 2 250 93.7 156.3 VV

Voltage across 3B is 3 250 VV

Power output

22

11

93.714 W

625

VW

R

2

2

156.323 W

1042W

2

3

25060 W

1042W

Hence 1 2 3W W W

Ans: (d)

14. The resistance between points A and B is

(a) 5 (b) 10

(c) 15 (d) 20

Sol: Equivalent resistance

4 4 2 10ABR Ans: (b)

8

4

8

8

4

6

B

A4

4

2

6 4 8

A

B

4

2

4

A

B

8/10/2019 55886aa

8/14

Current Electricity


ARevision Material

15. What is the potential difference between points C and D in the circuit shown

(a) 3.6 V (b) 7.2 V

(c) 1.2 V (d) 4.8 V

Sol: Current12

1.2A3 6 1

I

3 1.2 3.6 VD BV V

3.6DV V (1)

21 2

212 12 10.8

1 2C B

CV V

C C

210.8 7.2

3CV V (2)

From (1) and (2) 3.6 VC DV V

Ans: (a)

16.

Which of the following statements is current about the given circuit.

(a) Potential at P is 6 V

(b) Potential at Q is 1 V

(c) If voltmeter is connected across 6 V battery, it reads 7 V

(d) If voltmeter is connected across 6 V battery, it reads 6 V

16 ,1V 12 , 0.5V

4 0.5

P Q

SR

C

D

3 6 I

B

1 1C F 2 2C F

12V 1

A

8/10/2019 55886aa

9/14

Current Electricity


ARevision Material

Sol: Total resistance in the circuit 4 1 0.5 0.5 6R total emf 12 6 6v

Total current6 6

1 A6

iR

4 1 4 4 VPR P R PV V V V

0.5 0.5 VSQ S Q QV V V V V

6V battery is charging 6 1 7 VE ir

Ans: (d)

17.

What is the current flowing through the galvanometer in the circuit

(a) 10 A (b) 20 A

(c) 1 A (d) 0.01 A

Sol: Total resistance80 80

80 80 40 120160

Current in the circuit 22.4

2 10 A120

i

g gI G I I R

Ig2

22 10 8010 A 0.01 A

8 80

Ans: (d)

6V4 0.5

P Q

SR

1.5

80

2.4V

8080G

8/10/2019 55886aa

10/14

Current Electricity


ARevision Material

18. A uniform wire of resistance 4 is bent into the form of a circle of radius ' 'r . A specimen of the same

wire is connected along the diameter of the circle. What is equivalent resistance across the ends of the

wire?

(a)

4

1 (b)

4

4 (c)

2

4 (d)

4

4

Sol: Resistance per unit length2

R

r

Resistance of the wire along the diameter 22

Rr

r

'

RR

1 2 2 4 4

Re 4 4eff

RR

ff R R R R R

Ans: (b)

19. For the given circuit in steady state condition, the potential drop across the capacitor is

(a)3

V (b)

2

3

V

(c)5

V (d)

3

5

V

Sol: In steady state condition there is no current through capacitor, it acts as a open circuit

2

R

2

R

2

R

R

2

R

V

V

2V

R

C

2R

2R

V

V

2V

Ri

B

D

C

E

A

8/10/2019 55886aa

11/14

Current Electricity


ARevision Material

Applying KVL along :ACDEB

2 (2 ) 0A BV V V i R V

(2 ) 23 3

A BV V

V V V i R V RR

Ans: (b)

20. A battery of internal resistance 4 is connected to network of resistance as shown in stg. In order that

maximum power can be delivered to the network, the value of R in ohm should be

(a)4

5 (b)

8

7 (c) 9 (d) 2

Sol: Effective resistance in the circuit

2 2 42

2 2 4in

R R R RR R

R R R

In order to deliver maximum power, external resistance Internal resistance

4 2 2R R

Ans: (d)

RR

R

RR

6R

4R

, 4E

4R

2R

6R

R R

R

E 4

8/10/2019 55886aa

12/14

Current Electricity


ARevision Material

21. In the circuit shown, the current in the 1 resistor is 2 A . The power developed in the 3 resistor is

(a) 3 W (b) 9 W

(c) 27 W (d) 9.16 W

Sol:

AB CDV V

21 2ii i

2 2 12 1 2 1 , 2Ai i A i

Total current i 1 2 1 2 3Ai i

Current through 3 resistor is 3A

The power developed in 3 resistor2 2

3 3 27 Wi R

Ans: (c)

22. In the given circuit, the resistors of 2 and 3 together dissipate 30W of power. The current through

the 4 resistor is

(a) 0.5A (b) 1.5A

(c) 2.5A (d) 3.5A

1

2

3

1

2

3

B

DC

A

2

3

4

V

8/10/2019 55886aa

13/14

Current Electricity


ARevision Material

Sol:

Power2

V

R

2

V P R

2 630

5V

6V V

The current through 4 is6

1.5A4

Vi

R

Ans: (b)

23. The wires AB and ,BC each of length2

Lare made of the same material. The radius of wire AB is '2 'r

and of wire BC is r. The current I flows through the composite wire.

Choose the correct statement from the following

(a) .P D a cross BC is twice that across AB

(b) Power dissipated in BC is four times dissipated in AB

(c) Current densities in AB and BC are equal

(d) Electric fields in AB and BC are equal

Sol: Same current will flow through both the wires.

2 2

1 12 2

4 42AB BC

L L

R Rrr

(a) 4 4 4BC BC AC AC ABV iR i R iR V

2 3 6

2 3 5

4

V

2

L 2

L

IA B C

8/10/2019 55886aa

14/14

Documents

55886aa