Current Electricity

Two resistances of 100 and 200 are connected in series with a battery of 4 V and negligible internal resistance. A voltmeter is used to measure voltage across 100 resistance, which gives reading as 1 V. The resistance of voltmeter must be .

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

In the given circuit, the current flowing through the resistance 20 is 0.3 A, while the ammeter reads 0.9 A. The value of R1 is . [figure]

In the given figure, the charge stored in 6 capacitor, when points A and B are joined by a connecting wire is . [figure]

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