Current Electricity

Which of the following resistivity ( ) v/s temperature ( T ) curves is most suitable to be used in wire bound standard resistors?

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

Sliding contact of a potentiometer is in the middle of the potentiometer wire having resistance Rp=1 as shown in the figure. An external resistance of Re=2 is connected via the sliding contact. The electric current in the circuit is : [figure]

1. 1.35 A
2. 0.9 A
3. 1.0 A
4. 0.3 A

The equivalent resistance between A and B is : [figure]

1. 18
2. 27
3. 19
4. 25

The effective resistance between A and B, if resistance of each resistor is R, will be : [figure]

1. 8R3
2. 4R3
3. 23R
4. 5R3

In the given circuit, the terminal potential difference of the cell is : [figure]

1. 3 V
2. 4 V
3. 2 V
4. 1.5 V

Water boils in an electric kettle in 20 minutes after being switched on. Using the same main supply, the length of the heating element should be to times of its initial length if the water is to be boiled in 15 minutes.

1. increased, 34
2. increased, 43
3. decreased, 34
4. decreased, 43

The value of unknown resistance (x) for which the potential difference between B and D will be zero in the arrangement shown, is : [figure]

1. 3
2. 42
3. 6
4. 9

The number of electrons flowing per second in the filament of a 110 W bulb operating at 220 V is : (Given e = 1.6 10-19 C)

1. 1.25 1019
2. 31.25 1017
3. 6.25 1018
4. 6.25 1017

In the given figure R1 = 10 , R2 = 8 , R3 = 4 and R4 = 8 . Battery is ideal with emf 12 V. Equivalent resistance of the circuit and current supplied by battery are respectively : [figure]

1. 12 and 11.4 A
2. 10.5 and 1.14 A
3. 10.5 and 1 A
4. 12 and 1 A

The ratio of heat dissipated per second through the resistance 5 and 10 in the circuit given below is: [figure]

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

The resistances of the platinum wire of a platinum resistance thermometer at the ice point and steam point are 8 and 10 respectively. After inserting in a hot bath of temperature 400 , the resistance of platinum wire is :

1. 10
2. 16
3. 8
4. 2

To measure the internal resistance of a battery, potentiometer is used. For R=10 , the balance point is observed at l=500 cm and for R=1 the balance point is observed at l=400 cm. The internal resistance of the battery is approximately :

1. 0.1
2. 0.3
3. 0.2
4. 0.4

An electric bulb rated 50 W–200 V is connected across a 100 V supply. The power dissipation of the bulb is:

1. 100 W
2. 50 W
3. 12.5 W
4. 25 W

The reading in the ideal voltmeter (V) shown in the given circuit diagram is : [figure]

1. 3 V
2. 10 V
3. 5 V
4. 0 V

In a metre-bridge when a resistance in the left gap is 2 and unknown resistance in the right gap, the balance length is found to be 40 cm. On shunting the unknown resistance with 2 , the balance length changes by :

1. 62.5 cm
2. 22.5 cm
3. 20 cm
4. 65 cm

To measure the temperature coefficient of resistivity of a semiconductor, an electrical arrangement shown in the figure is prepared. The arm BC is made up of the semiconductor. The experiment is being conducted at 25 and resistance of the semiconductor arm is 3 m . Arm BC is cooled at a constant rate of 2 /s. If the galvanometer G shows no deflection after 10 s, then is : [figure]

1. -1 10-2 C-1
2. -2 10-2 C-1
3. -2.5 10-2 C-1
4. -1.5 10-2 C-1

Two conductors have the same resistances at 0 C but their temperature coefficients of resistance are 1 and 2. The respective temperature coefficients for their series and parallel combinations are :

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

By what percentage will the illumination of the lamp decrease if the current drops by 20%?

1. 26%
2. 36%
3. 46%
4. 56%

The resistance per centimeter of a meter bridge wire is r, with X resistance in left gap. Balancing length from left end is at 40 cm with 25 resistance in right gap. Now the wire is replaced by another wire of 2r resistance per centimeter. The new balancing length for same settings will be at

1. 10 cm
2. 80 cm
3. 40 cm
4. 20 cm

A potential divider circuit is shown in figure. The output voltage V0 is : [figure]

1. 2 mV
2. 4 V
3. 0.5 V
4. 12 mV

An electric toaster has resistance of 60 at room temperature (27 ). The toaster is connected to a 220 V supply. If the current flowing through it reaches 2.75 A, the temperature attained by toaster is around : ( if =2 10-4/ )

1. 1235
2. 1667
3. 694
4. 1694

When a potential difference V is applied across a wire of resistance R, it dissipates energy at a rate W. If the wire is cut into two halves and these halves are connected mutually parallel across the same supply, the energy dissipation rate will become:

1. 1/2W
2. 4W
3. 1/4W
4. 2W

The electric current through a wire varies with time as I=I0+ t, where I0=20 A and =3 A/s. The amount of electric charge crossed through a section of the wire in 20 s is :

1. 80 C
2. 800 C
3. 1000 C
4. 1600 C

In the given circuit, the current in resistance R3 is : [figure]

1. 2 A
2. 1.5 A
3. 1 A
4. 2.5 A

A wire of length 10 cm and radius 7 10-4 m is connected across the right gap of a meter bridge. When a resistance of 4.5 is connected on the left gap by using a resistance box, the balance length is found to be at 60 cm from the left end. If the resistivity of the wire is R 10-7 , then value of R is :

1. 63
2. 70
3. 66
4. 35

A wire of resistance R and length L is cut into 5 equal parts. If these parts are joined parallely, then resultant resistance will be :

1. 125R
2. 15R
3. 25 R
4. 5 R

Three voltmeters, all having different internal resistances are joined as shown in figure. When some potential difference is applied across A and B, their readings are V1, V2 and V3. Choose the correct option. [figure]

1. V1=V2
2. V1 V3-V2
3. V1+V2=V3
4. V1+V2>V3

Wheatstone bridge principle is used to measure the specific resistance (S1) of given wire, having length L, radius r. If X is the resistance of wire, then specific resistance is ; S1=X ( r2L ). If the length of the wire gets doubled then the value of specific resistance will be :

1. S14
2. 2 S1
3. S12
4. S1