Two cells of e.m.f. E and internal resistance r₁ and r₂ are connected in series through an external resistance R. The value of R for which the potential difference across one of the cells becomes zero will be:

1.  $\frac{{\mathrm{r}}_1{\mathrm{r}}_2}{{\mathrm{r}}_1 + {\mathrm{r}}_2}$ 

2.  ${\mathrm{r}}_1+{\mathrm{r}}_2$

3.  $\left|{\mathrm{r}}_2 - {\mathrm{r}}_1\right|$

4.  $\frac{{\mathrm{r}}_1}{{\mathrm{r}}_2}$

In the given circuit diagram, 3 identical bulbs are connected. If bulb B₃ get fused suddenly, how will the brightness of bulbs B₁ and B₂ change?
              

What is the reading of the voltmeter of resistance 1200 $\Omega$ connected in the following circuit diagram? 

1. 2.5 V

2. 5.0 V

3. 7.5 V

4. 40 V

The dependence of resistivity \((\rho)\) on the temperature \((T)\) of a semiconductor is, roughly, represented by:

1.		2.
3.		4.

Current through the \(2~\Omega\)$$ resistance in the electrical network shown is:

Two batteries, one of emf 18V and internal resistance 2 $\mathrm{\Omega }$ and the other of emf 12 V and internal resistance 1 $\mathrm{\Omega ,}$ are connected as shown. Reading of the voltmeter is:
(if voltmeter is ideal)

1.  14 V

2.  15 V

3.  18 V

4.  30 V

A current of 2 A is to be sent through a resistor of \(5 ~\Omega.\) Number of cells required in series, if each has emf 2 V and internal resistance 0.5 $\mathrm{\Omega }$, are:
1. 40
2. 30
3. 20
4. 10

A 50 kW dc generator produces a potential difference of 250 V. If the resistance of the transmission line is 1 $\Omega$, what percentage of the original power is lost during transmission?

1.  80%

2.  40%

3.  20%

4.  10%

A potential divider is used to give outputs of 2 V and 3 V from a 5 V source, as shown in the figure.

Which combination of resistances, from the ones given below, ${\mathrm{R}}_1,$ ${\mathrm{R}}_2,$ $\mathrm{and}$ ${\mathrm{R}}_3$ give the correct voltages?

Three voltmeters are connected as shown.

A potential difference is applied between A and B. On closing the switch S, readings of voltmeter (s):