Two cells when connected in series are balanced on 8m on a potentiometer. If the cells are connected with polarities of one of the cells  reversed, they balance on 2m. The ratio of e.m.f.'s of the two cells is

1. 3 : 5

2. 5 : 3

3. 3 : 4

4. 4 : 3

In the diagram shown, the reading of voltmeter is 20 V and that of ammeter is 4 A. The value of R should be (consider given ammeter and voltmeter are not ideal) :

1. Equal to 5 Ω

2. Greater from 5 Ω

3. Less than 5 Ω

4. Greater or less than 5 Ω depends on the material of R

Which is a wrong statement :

1. The Wheatstone bridge is most sensitive when all the four resistances are of the same order

2. In a balanced Wheatstone bridge, interchanging the positions of galvanometer and cell affects the balance of the bridge

3. Kirchhoff's first law (for currents meeting at a junction in an electric circuit) expresses the conservation of charge

4. The rheostat can be used as a potential divider

\(AB\) is a wire of uniform resistance. The galvanometer \(G\) shows no current when the length \(AC= 20~\text{cm}\) and \(CB = 80~\text{cm}\). The resistance \(R\) is equal to: 

1. \(2~\Omega\)
2. \(8~\Omega\)
3. \(20~\Omega\)
4. \(40~\Omega\)

The circuit shown here is used to compare the e.m.f. of two cells $E_1$ and $E_2(E_1>E_2)$. The null point is at C when the galvanometer is connected to E₁. When the galvanometer is connected to E₂, the null point will be 

1. To the left of C

2. To the right of C

3. At C itself

4. Nowhere on AB

In the Wheatstone's bridge (shown in the figure below) \(X=Y\) and \(A>B\). The direction of the current between \(a\) and \(b\) will be:

A resistance of 4 Ω and a wire of length 5 metres and resistance 5 Ω are joined in series and connected to a cell of e.m.f. 10 V and internal resistance 1 Ω. A parallel combination of two identical cells is balanced across 300 cm of the wire. The e.m.f. E of each cell is:

1. 1.5 V

2. 3.0 V

3. 0.67 V

4. 1.33 V

Constantan wire is used in making standard resistances because of its :

1. Specific resistance is low

2. Density is high

3. Temperature coefficient of resistance is negligible

4. Melting point is high

A potentiometer consists of a wire of length 4 m and resistance 10 Ω. It is connected to a cell of e.m.f. 2 V. The potential difference per unit length of the wire will be :

1. 0.5 V/m

2. 2 V/m

3. 5 V/m

4. 10 V/m

In the circuit shown $P\ne R$, the reading of the galvanometer is same with switch S open or closed. Then 

1. $I_R=I_G$

2. $I_P=I_G$

3. $I_Q=I_G$

4. $I_Q=I_R$