Current Electricity — Physics STD 12 Science — Question

Mark the correct options.

1. The luminous efficiency of a monochromatic source is always greater than that of a white light source of same power.
2. The luminous efficiency of a monochromatic source of wavelength 555nm is always greater than that of a white light source of same power.
3. The illuminating power of a monochromatic source of wavelength 555nm is always greater than that of a white light source of same power.
4. The illuminating power of a monochromatic source is always greater than that of a white light source of same power.

A biconvex lens made of a transparent material of refractive index 1.25 is immersed in water of refractive index 1.33. Will the lens behave as a converging or a diverging lens? Give reason.

Why a core of soft iron is used in a moving coil galvanometer?

For the same value of angle of incidence, the angles of refraction in three media A, B and C are 15°, 25° and 35° respectively. In which medium would the velocity of light be minimum?

Why does the energy of emitted photo-electrons vary even after shining light on the surface of a metal?

Mention the two characteristic properties of the material suitable for making core of a transformer.

If length of a wire of resistivity p is stretched to three times, then what will be new resistivity?

What is a Gaussian surface?

If the magnetic field outside a copper box is suddenly changed, what happens to the magnetic field inside the box? Such low-resistivity metals are used to form enclosures which shield objects inside them against varying magnetic fields.

A converging lens is kept coaxially in contact with a diverging lens – both the lenses being of equal focal lengths. What is the focal length of the combination?