Q

a

b

R

S

2Q

i

t

b)i

t

a)

i

t

d)i

t

c)

PHYSICS –CURRENT ELECTRICITY

1.. Two concentric conducting spherical shells of inner

radius a and outer radius b are shown in the figure.

Inner and outer shells are given charge Q and 2Q

respectively. Both the shells are connected through a

switch S and resistance R as shown at time t=0. The

current passing through the resistance is represented as

ANS: D

PASSAGE-

Three identical large metal planes a, b and c each of area A are placed at a sepearation as shown. Place C is initially uncharged, while plate a and b are given initial charge –Q and +Q respectively. A resistance R is also connected with a switch S. Initially switch S is open. Switch S is closed at time t = 0. At any time t charge on upper face of plane b is q1 and charge on the lower face of plate b is q2.

(Given

2. Before closing switch S, the energy stored between the plates a and c are

a) b) c) d)

Key: C

3.. Value of q1 is (in )

a) b) c) d)

Key: a

4.. Long time after the switch S is closed the value of q2 is

a) b) c) d)

Key : D

5.. Consider the coordinate axes as shown in the figure. Equation of the parabola is ---( i )

Now, consider an elementary capacitor at a distance ‘x’ from the axis of parabola as shown. Then the capacitance of this elementary capacitor will be

Now using equation( i ), we have

6.. Two conducing concentric hollow spheres of radii a and 2a respectively are shown in the diagram. The inner shell has net charge Q on its surface. The outer shell is neutral. If the outer shell is connected to the earth the heat generated through the connecting wire is

1) zero

2)

3)

4)

ANS: 3

7. Resistance of a wire is . It is drawn in such away that it experiences a longitudinal strain of 400%. The new resistance is

A) B) C) D)

Key.2

8. Resistance of a resistor at temperature is . Here is the resistance at . The

temperature coefficient of resistance at temperature is

A) B) C) D)

Key.3

9. A 220 V and 800 W electric kettle and three 220V and 100W bulbs are connected in parallel. On connecting this combination with 200V supply , the total current in the circuit will be

A) 0.15A B) 5A C) 5.5A D) 4.55A

Key;4

10. If = find the resistance in which maximum heat is generated if key K is closed

A) B) C) D)

Key;4

11. A conducting circular ring having 4 spokes of resistance rotated on a wire AB along a horizontal axile

OC. Wire AB and axle OC are connected to a battery of emf E. If how much current will flow

through if

A) B) E/2R C) E/R D) 2E/R

Key;2

12. Find the equivalent resistance between A and B :

A) 6R B) 5R C) 11R D) 20R

Key;3

13. A straight conductor of uniform cross section carries a current with electrons moving at a drift speed . The specific charge of an electron is proportional to:

A) B) C) D)

Key;4

14. Find the equivalent resistance about any branch of the base of the square pyramid shown. Assume resistance of each branch is R

A) B) C) D) none of these

Key;2

15. Find current

A) B) C) D) none of these

Key;2

16. The graph of a conductor at two different temperatuses is shown in fig. The ratio of temperature is

A) B) C) D)

Key;2

17. A plastic tube 25m long and 4 cm in diameter is dipped into Ag solution depositing a silver layer 0.1mm thick uniformly

overits outersurface. Find the current if this coated tube is connected across a 12V battery

A) 4.14A B) 41.4A C) 414A D) 414mA

Key;3

18. Open circuit voltage of a source is 7.86 V and its short circuit current is 9.25 A . Find the current when an external

resistance of 2.4 is connected

A) 1.4A B) 1.82A C) 2.01A D) 2.4A

Key;4

19. Find the current All the resistors shown have values in ohms

A) 1A B) 1.25A C) 2.0A D) 1.75A

Key;3

20. A wire of length L and 3 identical cells of negligible internal resistances are connected in series. Due to the current, the

temperature of the wire is raisied by in a time t. A number N of similar cells is now connected in series with a wire of the same material and cross-section but the length 2L The temperature of the wire is raised by the same amount

in the same t. The value of N is:

A) 3 B) 2 C) 6 D) 4

Key;3

21. Figure shows a metre bridge in which a known resistance R and an unknown resistance X connected to it.

The length of the total wire AB is 100cm. Then the balancing length for which the percentage error in

measuring the value of x is minimum (neglect end corrections)

a) 0 cm b) 33.3 cm c) 50 cm d) 100 cm

Ans: C

22 Two circular rings of same radii are made from similar wire of resistance each.They are placed in such a way that they cross each other’s centre C1,C2 as shown in figure. Conduction joints are made at intersection points A and B of the rings. An ideal cell of emf 20 volts is connected across AB. The power delivered by cell

is

1) 80 watt 2) 100watt 3) 120 watt 4)200watt

ANS: B

23. A cell dissipates the same power across each of two resistors R1 and R2 when connected separately. The internal resistance of cell is

(A) (B) (C) (D)

ANS: D

24. Ten equal resistances are connected as shown in the figure. A battery is to be so connected

that the power developed in the circuit is maximum. The battery should be connected

between (A)A and B (B) B and C(C) C and D (D)D and A.

ANS: D

25. The potentiometer wire AB is made of two equal parts AN and NB of cross sectional radii 2r and r respectively. The material of both parts is same. A cell is connected between A and B. The potential gradient in the part AN is 1 V/m. Potential difference between two points C and D (shown in figure) separated by 20 cm is found to be 0.5V. The separation between C and N. A C N D B

(A) 5 cm (B) 10 cm

(C) 12 cm (D) 15 cm

ANS: Key. B

26. Full scale deflection current for galvanometer is 1mA. What should be the value of shunt resistance (approximately) so that galvanometer shows half scale deflection.

G10A

A B

S

20G 10R

(A) (B)

(C) (D)Key. A

27. Figure shows a large conducting sheet having charge density on

its both surfaces. The surface potential of the sheet is with respect

to earth. A conducting sphere of radius r is placed at a separation

from the sheet as shown in figure. Find the charge that will appear on the sphere after it is connected to the earth

r

(A) (B)

(C) (D) zeroKey. A

28. A 6V battery with negligible internal resistance, is connected across a uniform wire of length

100cm. The positive terminal of another battery of emf 4V and internal resistance 1 is connected at A as shown in the figure. Take the potential at B to be zero and find out which of the following is correct?

(A) The potential at A is 6V and at C is 4V.

(B) The potential is 2V on AB at a distance of 33.33cms from A.

(C) If C is connected at 66.67cm from A then there will be no current in the 4V battery.

(D) If the 6V battery is replaced by a 12V battery then the potential at A would be 8V

ANS: C

29. A voltmeter of resistance R1 and an ammeter of resistance R2 are connected in series across a battery of negligible internal resistance. When a resistance of R is connected in parallel to the voltmeter, reading of ammeter increases three times while that of voltmeter reduces to one third. The value of

a) b) R1 is 3R c) d) R2 is 8R

ANS: C

30.. Circuit shown in figure is a simple ohm-meter, in which G is a galvanometer , Ro is a known resistance and R is the resistance which is to be measured. If A and B are short circuited by a resistance less wire, galvanometer gives full scale deflection. Then to read the resistance R

CA

4V

6V

B

1

directly from galvanometer, its scale would look like

(A) (B)

(C) (D)

ANS: A

31.. Figure shows a potentiometer wire AB of length 100 cm connected with an ideal cell of emf 5 volt. The key k is open. If the key k is closed then the balancing length x obtained on the potentiometer wire when galvanometer shows zero deflection is :

(A) 60 cm (B) 50 cm

(C) 45 cm (D) 40 cmANS: D

32.. Find the value of r so that maximum power is generated in external circuit.(A)r = 10 (B) r = 20 (C) r = 30 (D)r = 40 .

ANS: C

33.. The incorrect option in the given circuit if the reading of ammeter is zero is

(A) The value of 1 will be

(B) Current in R is

(C) Value of 1 will be

(D) Potential across 2R is zero.

ANS; C

34. In the arrangement shown in the figure when the switch S2 is open, the galvanometer shows no deflection for l = L/2. When the switch S2 is closed, the

galvanometer shows no deflection for l = . The internal resistance (r) of 6 V cell, and the emf E of the other battery are respectively

(a) 3 , 8 V (b) 2 , 12 V

(c) 2 , 24 V (d) 3 , 12 V

ANS: (b)

35. In the given figure, the value of R so that power generated in R will be maximum is

(A)

(B)

(C)

(D)

11 9

10 20 20

40

30

9V20 V

R30 V

ANS: D

36 Current -voltage characteristics of two elements A and B are as shown below in fig. (a) and (b)

(a) (b)

which of the following graph represents current voltage characteristic for the series combination ?(A) (B)

(C) (D)

ANS: A

37. There is an infinite grid of resistors shown in the diagram. The resistance of each resistance is R. The

equivalent resistance of the grid between two neighboring grid points is given by when the resistor joining them is removed. Then find the value of n. (L-3)

ANS : 2