Current Electricity

The effective resistance of a parallel connection that consists of four wires of equal length, equal area of cross-section and same material is 0.25 . What will be the effective resistance if they are connected in series?

1. 4
2. 0.25
3. 0.5
4. 1

Column - I gives certain physical terms associated with flow of current through a metallic conductor. Column-II gives some mathematical relations involving electrical quantities. Match column-I and column-II with appropriate relations.

1. (A)-(R); (B)-(Q); (C)-(S); (D)-(P)
2. (A)-(R); (B)-(S); (C)-(P); (D)-(Q)
3. (A)-(R); (B)-(S); (C)-(Q); (D)-(P)
4. (A)-(R); (B)-(P); (C)-(S); (D)-(Q)

Three resistors having resistances r1, r2 and r3 are connected as shown in the given circuit. The ratio i3i1 of currents in terms of resistances used in the circuit is : [figure]

1. r2r1+r3
2. r1r2+r3
3. r2r2+r3
4. r1r1+r2

A resistance wire connected in the left gap of a metre bridge balances a 10 resistance in the right gap at a point which divides the bridge wire in the ratio 3:2. If the length of the resistance wire is 1.5 m, then the length of 1 of the resistance wire is :

1. 1.0 10-1 m
2. 1.5 10-1 m
3. 1.5 10-2 m
4. 1.0 10-2 m

The color code of a resistance is given below : [figure] The values of resistance and tolerance, respectively, are

1. 47 k , 10%
2. 4.7 k , 5%
3. 470 , 5%
4. 470 k , 5%

A charged particle having drift velocity 7.5 10-4 m s-1 in an electric field of 3 10-10 V m-1 has a mobility in m2 V-1 s-1 of :

1. 2.5 106
2. 2.5 10-6
3. 2.25 10-15
4. 2.25 1015

Which of the following graph represents the variation of resistivity ( ) with temperature (T) for copper?

1. [figure]
2. [figure]
3. [figure]
4. [figure]

The solids which have the negative temperature coefficient of resistance are :

1. insulators only
2. semiconductors only
3. insulators and semiconductors
4. metals

Six similar bulbs are connected as shown in the figure with a DC source of emf E, and zero internal resistance. The ratio of power consumption by the bulbs when (i) all are glowing and (ii) in the situation when two from section A and one from section B are glowing, will be : [figure]

1. 4 : 9
2. 9 : 4
3. 1 : 2
4. 2 : 1

In the circuits shown below, the readings of voltmeters and the ammeters will be : [figure]

1. V1 = V2 and i1 = i2
2. V1 > V2 and i1 > i2
3. V1 > V2 and i1 = i2
4. V1 = V2 and i1 > i2

Which of the following acts as a circuit protection device?

1. inductor
2. conductor
3. switch
4. fuse

A set of n equal resistors, of value R each, are connected in series to a battery of emf E and internal resistance R. The current drawn is I. Now, the n resistors are connected in parallel to the same battery. Then the current drawn from battery becomes 10I. The value of n is

1. 10
2. 11
3. 20
4. 9

A battery consists of a variable number n of identical cells (having internal resistance r each) which are connected in series. The terminals of the battery are short-circuited and the current I is measured. Which of the graphs shows the correct relationship between I and n?

1. [figure]
2. [figure]
3. [figure]
4. [figure]

A carbon resistor of (47 4.7) k is to be marked with rings of different colours for its identification. The colour code sequence will be

1. Violet – Yellow – Orange – Silver
2. Yellow – Violet – Orange – Silver
3. Yellow – Green – Violet – Gold
4. Green – Orange – Violet – Gold

The resistance of a wire is 'R' ohm. If it is melted and stretched to 'n' times its original length, its new resistance will be

1. Rn
2. n2R
3. Rn2
4. nR

A potentiometer is an accurate and versatile device to make electrical measurements of EMF because the method involves

1. potential gradients
2. a condition of no current flow through the galvanometer
3. a combination of cells, galvanometer and resistances
4. cells

A potentiometer wire is 100 cm long and a constant potential difference is maintained across it. Two cells are connected in series first to support one another and then in opposite direction. The balance points are obtained at 50 cm and 10 cm from the positive end of the wire in the two cases. The ratio of emf's is

1. 3 : 4
2. 3 : 2
3. 5 : 1
4. 5 : 4

The charge flowing through a resistance R varies with time t as Q = at - bt2, where a and b are positive constants. The total heat produced in R is

1. a3R2b
2. a3Rb
3. a3R6b
4. a3R3b

The potential difference (VA - VB) between the points A and B in the given figure is [figure]

1. -3 V
2. +3 V
3. +6 V
4. +9 V

A filament bulb (500 W, 100 V) is to be used in a 230 V main supply. When a resistance R is connected in series, it works perfectly and the bulb consumes 500 W. The value of R is

1. 230
2. 46
3. 26
4. 13

Two metal wires of identical dimensions are connected in series. If 1 and 2 are their conductivities, the effective conductivity of the combination is

1. 1 + 2 1 2
2. 1 2 1 + 2
3. 2 1 2 1 + 2
4. 1 + 22 1 2

A potentiometer wire of length L and a resistance r are connected in series with a battery of e.m.f. E0 and a resistance r1. An unknown e.m.f. E is balanced at a length l of the potentiometer wire. The e.m.f. E will be given by

1. E0lL
2. LE0r(r + r1)l
3. LE0rlr1
4. E0r(r + r1) lL

A, B and C are voltmeters of resistance R, 1.5R and 3R respectively as shown in the figure. When some potential difference is applied between X and Y, the voltmeter readings are VA, VB and VC respectively, Then [figure]

1. VA = VB VC
2. VA VB VC
3. VA = VB = VC
4. VA VB = VC

Across a metallic conductor of non-uniform cross section a constant potential difference is applied. The quantity which remains constant along the conductor is

1. drift velocity
2. electric field
3. current density
4. current

A potentiometer wire has length 4 m and resistance 8 . The resistance that must be connected in series with the wire and an accumulator of e.m.f. 2 V, so as to get a potential gradient 1 mV per cm on the wire is

1. 44
2. 48
3. 32
4. 40

The resistances in the two arms of the meter bridge are 5 and R respectively. When the resistance R is shunted with an equal resistance, the new balance point is at 1.6 l1. The resistance R is [figure]

1. 10
2. 15
3. 20
4. 25

Two cities are 150 km apart. Electric power is sent from one city to another city through copper wires. The fall of potential per km is 8 volt and the average resistance per km is 0.5 . The power loss in the wire is

1. 19.2 W
2. 19.2 kW
3. 19.2 J
4. 12.2 kW

A potentiometer circuit has been set up for finding the internal resistance of a given cell. The main battery, used across the potentiometer wire, has an emf of 2.0 V and a negligible internal resistance. The potentiometer wire itself is 4 m long. When the resistance R, connected across the given cell, has values of (i) infinity, (ii) 9.5 , the balancing lengths on the potentiometer wire are found to be 3 m and 2.85 m, respectively. The value of internal resistance of the cell is

1. 0.25
2. 0.95
3. 0.5
4. 0.75

The resistances of the four arms P, Q, R and S in a Wheatstone's bridge are 10 ohm, 30 ohm, 30 ohm and 90 ohm, respectively. The e.m.f. and internal resistance of the cell are 7 volt and 5 ohm respectively. If the galvanometer resistance is 50 ohm, the current drawn from the cell will be

1. 0.1 A
2. 2.0 A
3. 1.0 A
4. 0.2 A

The internal resistance of a 2.1 V cell which gives a current of 0.2 A through a resistance of 10 is

1. 0.8
2. 1.0
3. 0.2
4. 0.5