Current Electricity

Two cells, having the same e.m.f. are connected in series through an external resistance R. Cells have internal resistances r1 and r2 (r1 > r2) respectively. When the circuit is closed, the potential difference across the first cell is zero. The value of R is

1. r1 + r2
2. r1 - r2
3. r1 + r22
4. r1 - r22

Power dissipated across the 8 Ω resistor in the circuit shown here is 2 watt. The power dissipated in watt units across the 3 Ω resistor is [figure]

1. 3.0
2. 2.0
3. 1.0
4. 0.5

Two batteries, one of emf 18 volts and internal resistance 2 and the other of emf 12 volts and internal resistance 1 , are connected as shown. The voltmeter V will record a reading of [figure]

1. 30 volt
2. 18 volt
3. 15 volt
4. 14 volt

When a wire of uniform cross-section a, length l and resistance R is bent into a complete circle, the resistance between any two diametrically opposite points will be

1. R/4
2. 4R
3. R/8
4. R/2

For the network shown in the figure the value of the current i is [figure]

1. 9V35
2. 18V5
3. 5V9
4. 5V18

A 5-ampere fuse wire can withstand a maximum power of 1 watt in the circuit. The resistance of the fuse wire is

1. 0.04 ohm
2. 0.2 ohm
3. 5 ohm
4. 0.4 ohm

The electric resistance of a certain wire of iron is R. If its length and radius are both doubled, then

1. The resistance will be doubled and the specific resistance will be halved.
2. The resistance will be halved and the specific resistance will remain unchanged.
3. The resistance will be halved and the specific resistance will be doubled.
4. The resistance and the specific resistance, will both remain unchanged.

Resistances n, each of r ohm, when connected in parallel give an equivalent resistance of R ohm. If these resistances were connected in series, the combination would have a resistance in ohms, equal to

1. n2R
2. R/n2
3. R/n
4. nR

Five equal resistances each of resistance R are connected as shown in the figure. A battery of V volts is connected between A and B. The current flowing in AFCEB will be [figure]

1. 3VR
2. VR
3. V2R
4. 2VR

A 6 volt battery is connected to the terminals of a three metre long wire of uniform thickness and resistance of 100 ohm. The difference of potential between two points on the wire separated by a distance of 50 cm will be

1. 2 volt
2. 3 volt
3. 1 volt
4. 1.5 volt