An electric motor which loaded has an effective resistance of 30 Ω and an inductive reactance of 40 Ω.If the motor is powered by a source with maximum voltage of 420 V, the maximum current is

• 6 A

• 8.4 A

• 10 A

• 12 A

An ammeter, voltmeter and a resistor are connected in series to a cell and the readings are noted as I and V. If another resistor R is connected in parallel with voltmeter, then

• I and V increase

• I increases

• I and V will remain same

• I decreases

One gram of copper is deposited in a copper voltameter when a current of 0.5 A flows for 30 minutes. Then, the current required to deposit 2g of silver in a silver voltmeter in the same time is (ece of copper = 3.3x10^-4 gC^-1, ece of silver = 1.1 x 10^-4 gC^-1)

• 4 A

• 6 A

• 3 A

• 5 A

54.

The amount of charge flowing per second per unit area normal to the flow is called

• electrical conductivity

• electrical resistivity

• mobility

• current density

Two bulbs of equal power are connected in parallel and they totally consume 110 W at 220 V. The resistances of each bulb is

• 550 Ω

• 440 Ω

• 330 Ω

• 880 Ω

The resistivity of the material of potentiometer wire is 5 × 10^-6 Ω m and its area of cross-section is 5 × 10^-6 m m². If 0.2 A curent is flowing through the wire, then the potential through the wire, then the potential drop per metre length of the wire is 

• 0.1 Vm^-1

• 0.5 Vm^-1

• 0.25 Vm^-1

• 0.2 Vm^-1

A battery of 6V and internal resistance 2 Ω is connected to a silver voltmeter. If the current of 1.5 A flows through the circuit, the resistance of the voltmeter is

• 4 Ω

• 2 Ω

• 6 Ω

• 1 Ω

The ratio of resistances of two copper wires of the same length and of same cross-sectional area when connected in series to that when connected in parallel is

• 1 : 1

• 1 : 2

• 2 : 1

• 4 : 1

A flow of 10⁶ electrons per second in a conducting wire constitutes a flow of current

• 1.6 × 10^-15 A

• 1.6 × 10^-11 A

• 1.6 × 10^-13 A

• 1.6 × 10^-19 A

Five cells each of emf E and internal resistance r send the same amount of current through an external resistance R whether the cells are connected in parallel or in series. Then the ratio $\left(\frac{\mathrm{R}}{\mathrm{r}}\right)$ is

• 2

• $\frac{1}{2}$

• $\frac{1}{5}$

• 1