91.

The magnification produced by the objective lens and the eye lens of a compound microscope are 25 and 6  respectively. The magnification of this microscope is

• 25

• 50

• 150

• 200

J.J. Thomson's cathode ray tube experiment demonstrated that

• cathode rays are streams of negatively charged ions

• all the mass of an atom is essentially in the nucleus

• the e/m of electrons is much greater than the e/m of protons

• the e/m ratio of the cathode ray particles changes when a different gas is placed in the discharge tube

Wavelength of light emitted from second orbit to first orbit in a hydrogen atom is

• 6563 $\stackrel{\circ }{\mathrm{A}}$

• 4102 $\stackrel{\circ }{\mathrm{A}}$

• 4861 $\stackrel{\circ }{\mathrm{A}}$

• 1215 $\stackrel{\circ }{\mathrm{A}}$

If M is atomic mass, A is mass number of a nucleus, then $\frac{\mathrm{M} - \mathrm{A}}{\mathrm{A}}$ is called

• mass defect

• fermi energy

• binding energy

• packing fraction

The half-life of a radio-isotope is 4 h. If initial mass of the isotope was 200 g, then mass remaining after 24 h will be

• 1.042 g

• 2.084 g

• 3.125 g

• 4.167 g

A radioactive nucleus A finally transforms into a stable nucleus B. Then A and B can be

• isobars

• isotones

• isotopes

• none of these

If ₉₂U²³⁸ emits 8 $\mathrm{\alpha }$-particles and 6 β-particles, then the resulting nucleus is

• ₈₂U²⁰⁶

• ₈₂Pb²⁰⁶

• ₈₂U²¹⁰

• ₈₂U²¹⁴

Carbon, silicon and germanium atoms have four valence electrons each. Their valence and conduction bands are separated by energy band gaps represented by (E_g)_C , (E_g )_Si , and (E_g)_Ge  respectively. Which one of the following relationships is true in their case ?

• (E_g)_C > (E_g)_Si

• (E_g)_C = (E_g)_Si

• (E_g)_C < (E_g)_Ge

• (E_g)_C < (E_g)_Si

Then n-type semiconductors are obtained, when germanium is doped with

• arsenic

• phosphorus

• antimony

• any one of these

Which logic gate is represented by the following combination of logic gates ?

• OR

• NOR

• AND

• NAND