In a closed circuit, the current I (in ampere) at an instant of time t (in second) is given by I = 4 − 0.08 t. The number of electrons flowing in 50 s through the cross- section of the conductor is

• 1.25 × 10¹⁹ 

• 6.25 × 10²⁰

• 5.25 × 10¹⁹

• 2.55 × 10²⁰

102.

If R₁ and R₂ be the resistances of the filaments of 200 W and 100 W electric bulbs operating at 220 V, then $\left(\frac{{\mathrm{R}}_1}{{\mathrm{R}}_2}\right)$ is

• 1

• 2

• 0.5

• 4

A potentiometer wire, 10 m long, has a resistance of 40 Ω. It is connected in series with a resistance box and a 2 V storage cell. If the potential gradient along the wire is (0.1 mV / cm), the resistance unplungged in the box is

• 260 Ω

• 760 Ω

• 960 Ω

• 1060 Ω

When a current I flows through a wire, the drift velocity of the electrons is v. When current 2I flows through another wire of the same material having double the length and double the area of cross-section, the drift velocity of the electrons will be

• $\frac{\mathrm{v}}{8}$

• $\frac{\mathrm{v}}{4}$

• $\frac{\mathrm{v}}{2}$

• v

Two identical cells whether connected in parallel or in series gives the same current when connected to an external resistance 1.5 Ω. Find the value of internal resistance of each cell.

• 1 Ω

• 0.5 Ω

• 1.5 Ω

• zero

Two identical cells send the same current in 3 Ω resistance, whether connected in series or in parallel. The internal resistance of the cell should be

• 1 Ω

• 3 Ω

• $\frac{1}{2} \mathrm{\Omega }$

• 3.5 Ω

The ratio of the resistance of conductor at temperature 15°C to its resistance at temperature 37.5°C is 4 : 5. The temperature coefficient of resistance the conductor is

• $\frac{1}{25}°{\mathrm{C}}^{-1}$

• $\frac{1}{50}°{\mathrm{C}}^{-1}$

• $\frac{1}{80}°{\mathrm{C}}^{-1}$

• $\frac{1}{75}°{\mathrm{C}}^{-1}$

In which of the following substances does resistance decrease with increase in temperature ?

• Copper

• Carbon

• Constantant

• Silver

Resistors P and Q are connected in the gaps of the meter bridge. The balancing point is obtained $\frac{1}{3} \mathrm{m}$  from the zero end. If a 6 Ω resistance is connected in series with P the balance point shifts to $\frac{2}{3}$ m from the same end. P and Q are

• 4, 2

• 2, 4

• both (a) and (b)

• neither (a) nor (b)

The currents i₁ and i₂ through the resistors R₁ (= 10 Ω) and R₂ (= 30 Ω) in the circuit diagram with E₁ =3V, E₂ = 3V and E₃ = 2V are respectively

• 0.2 A, 0.1 A

• 0.4 A, 0.2 A

• 0.1 A, 0.2 A

• 0.2 A, 0.4 A