Current Electricity

In a meter bridge experiment to determine the value of unknown resistance, first the resistances 2 and 3 are connected in the left and right gaps of the bridge and the null point is obtained at a distance l cm from the left. Now when an unknown resistance x is connected in parallel to 3 resistance, the null point is shifted by 10 cm to the right of wire. The value of unknown resistance x is .

A wire of uniform resistance /m is bent into a circle of radius r and another piece of wire with length 2r is connected between points A and B (AOB) as shown in figure. The equivalent resistance between points A and B is . [figure]

1. ( + 1)2r
2. 6 r3 + 16
3. 3 r8
4. 2 r

A meter bridge with two resistances R1 and R2 as shown in figure was balanced (null point) at 40 cm from the point P. The null point changed to 50 cm from the point P, when 16 resistance is connected in parallel to R2. The values of resistances R1 and R2 are . [figure]

1. R2 = 8 , R1 = 163
2. R2 = 12 , R1 = 123
3. R2 = 4 , R1 = 43
4. R2 = 16 , R1 = 163

An electric power line having total resistance of 2 , delivers 1 kW of power at 250 V. The percentage efficiency of transmission line is .

1. 96.9
2. 92.5
3. 86.5
4. 100

A cylindrical conductor of length 2 m and area of cross-section 0.2 mm2 carries an electric current of 1.6 A when its ends are connected to a 2 V battery. Mobility of electrons in the conductor is 10-3 m2/V s. The value of is : (electron concentration = 5 1028 /m3 and electron charge = 1.6 10-19 C)

The heat generated in 1 minute between points A and B in the given circuit, when a battery of 9 V with internal resistance of 1 is connected across these points is J. [figure]

Two known resistances of R and 2R and one unknown resistance X are connected in a circuit as shown in the figure. If the equivalent resistance between points A and B in the circuit is X , then the value of X is . [figure]

1. 2( 3 - 1)R
2. R
3. ( 3 - 1)R
4. ( 3 + 1)R

The total length of potentiometer wire AB is 50 cm in the arrangement as shown in the figure. If P is the point where the galvanometer shows zero reading then the length AP is cm. [figure]

1. 25
2. 30
3. 15
4. 20

A battery with EMF E and internal resistance r is connected across a resistance R. The power consumption in R will be maximum when:

1. R = 2r
2. R = 2r
3. R = r2
4. R = r

A wire of resistance R is bent into a triangular pyramid as shown in figure with each segment having same length. The resistance between points A and B is R/n. The value of n is : [figure]

1. 16
2. 10
3. 12
4. 14