Current Electricity

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