In a series L-C-R circuit, an alternating emf (V) and current (i) are given by the equation $\mathrm{V} = {\mathrm{V}}_0 \sin \mathrm{\omega t}, \mathrm{I} = {\mathrm{I}}_0 \sin \left(\mathrm{\omega t} + \frac{\mathrm{\pi }}{3}\right)$. The average power dissipated in the circuit over a cycle of AC is

• $\frac{{\mathrm{V}}_0{\mathrm{I}}_0}{2}$

• $\frac{{\mathrm{V}}_0{\mathrm{I}}_0}{4}$

• $\frac{\sqrt{3}}{2} {\mathrm{V}}_0{\mathrm{I}}_0$

• zero

Electromagnetic radiation used to sterilise milk is 

• X-rays

• γ-rays

• UV rays

• Radio waves

The process of superimposing message signal on high frequency carrier wave is called

• amplification

• demodulation

• transmission

• modulation

A plane glass plate is placed over a various coloured letters (violet, green, yellow, red). The letter which appears to raised more is

• red

• yellow

• green

• violet

A ray of light passes through four transparent media with refractive index n₁, n₂, n₃ and n₄ as shown in the figure. The surfaces of all media are parallel.

If the emergent ray DE is parallel to incident ray AB, then

• n₁ = n₄ 

• n₂ = n₄

• n₃ = n₄

• ${\mathrm{n}}_1 = \frac{{\mathrm{n}}_2 + {\mathrm{n}}_3 + {\mathrm{n}}_4}{3}$

46.

Focal length of a convex lens is 20 cm and its refractive index is 1.5. It produces an erect, enlarged image if the distance of the object from the lens is

• 40 cm

• 30 cm

• 15 cm

• 20 cm

A ray of light suffers a minimum deviation when incident on an equilateral prism of refractive index $\sqrt{2}$. The angle of deviation is

• 30°

• 45°

• 60°

• 50°

In Young's double slit experiment, the source is white light. One slit is covered with red filter and the other with blue filter. There shall be

• alternate red and blue fringes

• alternate dark and pink fringes

• alternate dark and yellow fringes

• no interference

Light of wavelength 600 nm is incident normally on a slit of width 0.2 mm. The angular width of central maxima in the diffraction pattern is (measured from minimum to minimum)

• 6 × 10^-3 rad

• 4 × 10^-3 rad

• 2.4 × 10^-3 rad

• 4.5 × 10^-3 rad

For what distance ray optics is good approximation when the aperture is 4 mm and the wavelength of light is 400 nm ?

• 24 m

• 40 m

• 18 m

• 30 m