51.

The self-inductance of a long solenoid carrying current is independent of

• its length

• the current

• its cross-sectional area

• magnetic permeability of the core

The rms value of AC which when passed through a resistor produces heat, which is twice that produced by a steady current of 1.414 A in the same resistor is

• 2 A

• 3.46 A

• 2.818 A

• 1.732 A

In a series LCR AC circuit, the current is maximum when the impedance is equal to

• the reactance

• the resistance

• zero

• twice the reactance

γ-rays are detected by

• point contact diodes

• thermopiles

• ionization chamber

• photocells

If the directions of electric and magnetic field vectors of a plane electromagnetic wave are along positive y- direction and positive z-direction respectively, then the direction of propagation of the wave is along

• positive z-direction

• negative z-direction

• negative y-direction

• positive x-direction

When an object is viewed with a light of wavelength 6000 $\stackrel{\circ }{\mathrm{A}}$ under a microscope, its resolving power is 10⁴. The resolving power of the microscope when the same object is viewed with a light of wavelength 4000 $\stackrel{\circ }{\mathrm{A}}$, is

• 10⁴

• 2 × 10⁴

• 1.5 × 10⁴

• 3 × 10⁴

Secondary rainbow in the atmosphere is

• the result of polarization and dispersion of light

• brighter than the primary rainbow

• formed due to two reflections in the rain drop

• formed with red colour on the top

For a diffraction from a single slit, the intensity of the central point is

• infinite

• finite and same magnitude as the surrounding maxima

• finite but much larger than the surrounding maxima

• finite and substantially smaller than the surrounding maxima

If the radius of curvature of the curved surface of a plano -convex lens is 50 cm, its focal length is (µ =1.5)

• 0.5 m

• 0.75 m

• 1 m

• 0.25 m

The magnification of an image by a convex lens is positive only when the object is placed

• at its focus F

• between F and 2F

• at 2F

• between F and optical centre