371.

A battery of four cells in series,each having an emf of 1 .4 V and an internal resistance of 2 $\mathrm{\Omega }$ is to be used to charge a small 2 V accumulator of negligible internal resistance. What is the charging current?

• 0.1 A

• 0.2 A

• 0.3 A

• 0.45 A

An ammeter reads upto 1 A. Its internal resistance is 0.81 Ω. To increase the range to 10 A, the value of the required shunt is

• 0.03 Ω

• 0.3 Ω

• 0.9 Ω

• 0.09 Ω

The length of a wire of a potentiometer is 100 cm, and the emf of its stand and cell is E volt. It is employed to measure the emf of a battery whose internal resistance is 0.52 Ω.1fthe balance point is obtained at l= 30 cm from the positive end, the emf of the battery is

• $\frac{30\mathrm{E}}{100.5}$

• $\frac{30\mathrm{E}}{100 - 0.5}$

• $\frac{30 (\mathrm{E} - 0.5\mathrm{i})}{100},\mathrm{where} \mathrm{i} \mathrm{is} \mathrm{the} \mathrm{current} \mathrm{in} \mathrm{the} \mathrm{potentiometer} \mathrm{wire}$

• $\frac{30\mathrm{E}}{100}$

The material of wire of potentiometer is made of

• copper

• steel

• manganin

• aluminium

A potential difference V is applied at the ends of a copper wire of length l and diameter d. On doubling only d, drift velocity

• becomes two times

• becomes half

• does not change

• becomes one-fourth

Temperature of a piece of silicon is raised from 27°C to 100°C, then its conductivity

• increases

• decreases

• remains same

• becomes zero

Work of invertor is

• to change AC into DC

• to change DC into AC

• to regulate voltage

• None of the above

Ten wires each of resistance 1 Ω are connected in parallel, then total resistance will be

• 10 Ω

• 1 Ω

• 0.1 Ω

• 0.001 Ω

A wire of radius r has resistance R. If it is streched to a radius of $\frac{3\mathrm{r}}{4}$. Its resistance becomes

• $\frac{256 \mathrm{R}}{81}$

• $\frac{81 \mathrm{R}}{256}$

• $\frac{16 \mathrm{R}}{9}$

• $\frac{9 \mathrm{R}}{16}$

A drift velocity offree electrons in a conductor is v_d, when the current i is flowing in it. If both the radius and current are doubled, the drift velocity will be

• $\frac{{\mathrm{V}}_{\mathrm{d}}}{8}$

• $\frac{{\mathrm{V}}_{\mathrm{d}}}{4}$

• $\frac{{\mathrm{V}}_{\mathrm{d}}}{2}$

• V_d