In a circuit, the current lags behind the voltage by a phase difference of π/2, the circuit will contain which of the following?

• Only R

• Only C

• R and C

• Only L

Which of the following has the minimum resistance?

• Voltmeter

• Millivoltmeter

• Ammeter

• Milliameter

N identical cells, each of emf E, are connected in parallel. The emf of the combination is

• NE

• E

• N²E

• E/N

A 30 µF capacitor is charged by a constant current of 30 mA. If the capacitor is initially uncharged, how long does it take for the potential difference to reach 400 V?

• 0.2 s

• 0.4 s

• 0.6 s

• 0.8 s

45.

Therm-ions are

• photons

• protons

• electrons

• nuclei

The intensity of sound gets reduced by 10% on passing through a slab. The reduction in intensity on passing through two consecutive slabs would be

• 20 %

• 19 %

• 5 %

• 50 %

Four independent waves are expressed as

$$\begin{gathered} \left(\mathrm{i}\right) {\mathrm{y}}_1 = {\mathrm{a}}_1\mathrm{sin\omega t} \\ \left(\mathrm{ii}\right) {\mathrm{y}}_2 = {\mathrm{a}}_2\mathrm{sin\omega t} \\ \left(\mathrm{iii}\right) {\mathrm{y}}_3 = {\mathrm{a}}_3\mathrm{cos\omega t} \\ \left(\mathrm{iv}\right) {\mathrm{y}}_4 = {\mathrm{a}}_4\sin \left(\mathrm{\omega t} + \frac{\mathrm{\pi }}{3}\right) \end{gathered}$$

• (i) and (iii)

• (i) and (iv)

• (ii) and (iv)

• not possible at all

Two coherent monochromatic light beams of intensities I and 4 I superimpose. The maximum and minimum possible intensities in the resulting beam are respectively

• 5I and I

• 5I and 3I

• 3I and I

• 9I and I

Ordinary light incident on a glass slab at the polarising angle suffers a deviation of 22°. The value of the angle of refraction in glass in this case is

• 56°

• 68°

• 34°

• 22°

A radioisotope has a half-life of 5 yr. The fraction of the atoms of this material that would decay in 15 yr will be

• 1

• 2/3

• 7/8

• 5/8