Current Electricity

Two rods are joined end to end, as shown. Both have a cross-sectional area of 0.01 cm2. Each is 1 meter long. One rod is of copper with a resistivity of 1.7 10-6 ohm-centimeter, the other is of iron with a resistivity of 10-5 ohm-centimeter. [figure] How much voltage is required to produce a current of 1 ampere in the rods?

1. 0.00145 V
2. 0.0145 V
3. 1.7 10-6 V
4. 0.117 V

A 12 cm wire is given a shape of a right angled triangle ABC having sides 3 cm, 4 cm and 5 cm as shown in the figure. The resistance between two ends (AB, BC, CA) of the respective sides are measured one by one. Their ratio is [figure]

1. 9 : 16 : 25
2. 27 : 32 : 35
3. 21 : 24 : 25
4. 3 : 4 : 5

Ten identical cells connected in series are needed to heat a wire of length one meter and radius 'r' by 10 in time 't'. How many cells will be required to heat the wire of length two meter of the same radius by the same temperature in time 't' ?

1. 20
2. 30
3. 40
4. 10

A cell having an emf and internal resistance r is connected across a variable external resistance R. As the resistance R is increased, the plot of potential difference V across R is given by

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

The power dissipated in the circuit shown in the figure is 30 watts. The value of R is [figure]

1. 20
2. 15
3. 10
4. 30

In the circuit shown the cells A and B have negligible resistances. For VA = 12 V, R1 = 500 and R = 100 the galvanometer (G) shows no deflection. The value of VB is [figure]

1. 4 V
2. 2 V
3. 12 V
4. 6 V

A ring is made of a wire having a resistance R0 = 12 . Find the points A and B, as shown in the figure, at which a current carrying conductor should be connected so that the resistance R of the sub circuit between these points is equal to 83 . [figure]

1. l1l2 = 58
2. l1l2 = 13
3. l1l2 = 38
4. l1l2 = 12

If voltage across a bulb rated 220 volt-100 watt drops by 2.5% of its rated value, the percentage of the rated value by which the power would decrease is

1. 20%
2. 2.5%
3. 5%
4. 10%

In the circuit shown in the figure, if the potential at point A is taken to be zero, the potential at point B is [figure]

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

A current of 2 A flows through a 2 Ω resistor when connected across a battery. The same battery supplies a current of 0.5 A when connected across a 9 Ω resistor. The internal resistance of the battery is

1. 0.5 Ω
2. 1/3 Ω
3. 1/4 Ω
4. 1 Ω

If power dissipated in the 9 Ω resistor in the circuit shown is 36 watt, the potential difference across the 2 Ω resistor is [figure]

1. 4 volt
2. 8 volt
3. 10 volt
4. 2 volt

Consider the following two statements. Which of the following is correct?

1. Both (A) and (B) are wrong
2. (A) is correct and (B) is wrong
3. (A) is wrong and (B) is correct
4. Both (A) and (B) are correct

A potentiometer circuit is set up as shown. The potential gradient, across the potentiometer wire, is k volt/cm and the ammeter, present in the circuit, reads 1.0 A when two way key is switched off. The balance points, when the key between the terminals (i) 1 and 2 (ii) 1 and 3, is plugged in, are found to be at length l1 cm and l2 cm respectively. The magnitudes, of the resistors R and X, in ohms, are then, equal, respectively, to [figure]

1. k(l2 - l1) and kl2
2. kl1 and k(l2 - l1)
3. k(l2 - l1) and kl1
4. kl1 and kl2

See the electrical circuit shown in this figure. Which of the following equations is a correct equation for it ? [figure]

1. 2 - i2r2 - 1 - i1r1 = 0
2. - 2 - (i1 + i2)R + i2r2 = 0
3. 1 - (i1 + i2)R + i1r1 = 0
4. 1 - (i1 + i2)R - i1r1 = 0

A wire of resistance 12 ohms per metre is bent to form a complete circle of radius 10 cm. The resistance between its two diametrically opposite points, A and B as shown in the figure is [figure]

1. 3
2. 6
3. 6
4. 0.6

A student measures the terminal potential difference (V) of a cell (of emf and internal resistance r) as a function of the current (I) flowing through it. The slope, and intercept, of the graph between V and I, then respectively, equal

1. -r and
2. r and -
3. - and r
4. and -r

The mean free path of electrons in a metal is 4 10-8 m. The electric field which can give on an average 2 eV energy to an electron in the metal will be in units V/m

1. 5 10-11
2. 8 10-11
3. 5 107
4. 8 107

[figure] In the circuit shown, the current through the 4 resistor is 1 amp when the points P and M are connected to a d.c. voltage source. The potential difference between the points M and N is

1. 0.5 volt
2. 3.2 volt
3. 1.5 volt
4. 1.0 volt

A wire of a certain material is stretched slowly by ten percent. Its new resistance and specific resistance become respectively

1. both remain the same
2. 1.1 times, 1.1 times
3. 1.2 times, 1.1 times
4. 1.21 times, same

A cell can be balanced against 110 cm and 100 cm of potentiometer wire, respectively without and with being short circuited through a resistance of 10 . Its internal resistance is

1. 2.0 ohm
2. zero
3. 1.0 ohm
4. 0.5 ohm

An electric kettle takes 4 A current at 220 V. How much time will it take to boil 1 kg of water from temperature 20 ? The temperature of boiling water is 100

1. 12.6 min
2. 4.2 min
3. 6.3 min
4. 8.4 min

A current of 3 amp. flows through the 2 resistor shown in the circuit. The power dissipated in the 5 resistor is [figure]

1. 1 watt
2. 5 watt
3. 4 watt
4. 2 watt

Three resistances, P, Q, R each of 2 and an unknown resistance S form the four arms of a Wheatstone bridge circuit. When a resistance of 6 is connected in parallel to S the bridge gets balanced. What is the value of S?

1. 3
2. 6
3. 1
4. 2

The total power dissipated in watt in the circuit shown here is [figure]

1. 40
2. 54
3. 4
4. 16

In the circuit shown, if a conducting wire is connected between points A and B, the current in this wire will [figure]

1. flow from B to A
2. flow from A to B
3. flow in the direction which will be decided by the value of V
4. be zero

Kirchhoff's first and second laws of electrical circuits are consequences of

1. conservation of energy and electric charge respectively
2. conservation of energy
3. conservation of electric charge and energy respectively
4. conservation of electric charge

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