Ray Optics and Optical Instruments — Physics STD 12 Science — Question

A triode is operated in the linear region of its characteristics. If the plate voltage is slightly increased, the dynamic plate resistance will:

A 25 watt, 220 volt bulb and a 100 watt, 220 volt bulb are connected in series across a 220 volt lines. Which electric bulb will glow more brightly(a) 25 watt bulb(b) 100 watt bulb(c) First 25 watt and then 100 watt(d) Both with same brightness

If heat is supplied to an ideal gas in an isothermal process:

1. The internal energy of the gas will increase.
2. The gas will do positive work.
3. The gas will do negative work.
4. The said process is not possible.

The ratio of the speed of the electrons in the ground state of hydrogen to the speed of light in vacuum is(a) 1/2     (b) 2/137(c) 1/137 (d) 1/237

The ratio of the largest to shortest wavelengths in Lyman series of hydrogen spectra is

Assertion  :   Fuse wire must have high resistance and low melting point.
Reason    : Fuse is used for small current flow only.(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.(c) If assertion is true but reason is false.(d) If the assertion and reason both are false.

When light rays from the sun fall on a convex lens along a direction parallel to its axis (a) Focal length for all colours is the same(b) Focal length for violet colour is the shortest(c) Focal length for yellow colour is the longest(d) Focal length for red colour is the shortest

A dielectric slab is inserted between the plates of a capacitor. The charge on the capacitor is Q and the magnitude of the induced charge on each surface of the dielectric is Q':

The minimum wavelength of X-rays produced in a coolidge tube operated at potential difference of 40 kV is(a) 0.31 Å(b) 3.1 Å(c) 31 Å    (d) 311 Å