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
4102
4861
1215
If M is atomic mass, A is mass number of a nucleus, then 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 -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 (Eg)C , (Eg )Si , and (Eg)Ge respectively. Which one of the following relationships is true in their case ?
(Eg)C > (Eg)Si
(Eg)C = (Eg)Si
(Eg)C < (Eg)Ge
(Eg)C < (Eg)Si
A.
(Eg)C > (Eg)Si
Carbon, silicon and germanium are semiconductors.
(Eg)C = 5.2 eV
(Eg)Si = 1.21 eV
(Eg)Ge = 0.75 eV
Thus, (Eg)C > (Eg)Si and (Eg)C > (Eg)Ge
Then n-type semiconductors are obtained, when germanium is doped with
arsenic
phosphorus
antimony
any one of these