Figure below shows four plates each of area A and separated from one another by a distance d. What is the capacitance between P and Q ?

• $\frac{{\mathrm{\epsilon }}_0\mathrm{A}}{\mathrm{d}}$

• $\frac{2{\mathrm{\epsilon }}_0\mathrm{A}}{\mathrm{d}}$

• $\frac{3{\mathrm{\epsilon }}_0\mathrm{A}}{\mathrm{d}}$

• $\frac{4{\mathrm{\epsilon }}_0\mathrm{A}}{\mathrm{d}}$

42.

A soap bubble is charged to a potential of 16 V. Its radius is, then doubled. The potential of the bubble now will be

• 16 V

• 8 V

• 4 V

• 2 V

A parallel plate capacitor of capacitance 10 F is charged to 1 µC. The charging battery is removed and then the separation between the plates is doubled. Work done during the process is

• 5 mJ

• 0.05 mJ

• 1 mJ

• 10 mJ

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

An α-particle with a specific charge of 2.5 × 10⁷ C kg^-1 moves with a speed of 2 x 10⁵ ms^-1 in a perpendicular magnetic field of 0.05 T. Then the radius of the circular path described by it is

• 8 cm

• 4 cm

• 16 cm

• 2 cm

A cyclotron can be used to accelerate

• α-particles

• β-particles

• neutrons

• neutrino

The magnitude of the earth's magnetic field at a place is B₀ and the angle of dip is δ. A horizontal conductor of length l lying magnetic north-south moves eastwards with a velocity v. The emf induced across the conductor is

• zero

• B₀ lv sin δ

• B₀ lv

• B₀ lv cos δ

A milliammeter of range 0- 30 mA has internal resistance of 20 Ω. The resistance to be connected in series to convert it into a voltmeter of maximum reading 3V is

• 49 Ω

• 80 Ω

• 40 Ω

• 30 Ω