Atoms — Physics STD 12 Science — Question

X-rays are not used for radar purpose because(a) They are not reflected by the target(b) They are not electromagnetic waves(c) They are completely absorbed by the air(d) They sometimes damage the target

Lux is equal to 

A achromatic combination is made with a lens of focal length f and dispersive power ω with a lens having dispersive power of 2ω. The focal length of second will be(a) 2f (b) f/2 (c) -f/2 (d) – 2 f

A point source of light is placed 4 m below the surface of water of refractive index 5 / 3. The minimum diameter of a disc which should be placed over the source on the surface of water to cut–off all light coming out of water is(a) 2 m(b) 6 m(c) 4 m(d) 3 m

Light of wavelength 589.3 nm  is incident normally on the slit of width 0.1 mm. What will be the angular width of the central diffraction maximum at a distance of 1 m  from the slit(a) 0.68°(b) 1.02°(c) 0.34°  (d) None of these

The masses of neutron and proton are 1.0087 a.m.u. and 1.0073  a.m.u. respectively. If the neutrons and protons combine to form a helium nucleus (alpha particles) of mass 4.0015 a.m.u. The binding energy of the helium nucleus will be (1 a.m.u.= 931 MeV)(a) 28.4  MeV(b) 20.8  MeV(c) 27.3  MeV(d) 14.2  MeV

The penetrating power of X-rays depends upon :

The hyper-metropia is a(a) Short-side defect(b) Long- side defect(c) Bad vision due to old age(d) None of these

Angular width of central maxima in the Fraunhoffer diffraction pattern of a slit is measured. The slit is illuminated by light of wavelength 6000 Å. When the slit is illuminated by light of another wavelength, the angular width decreases by 30%. The wavelength of this light will be(a) 6000 Å(b) 4200 Å(c) 3000 Å(d) 1800 Å