[2014]
5.
[2014]
[2013]
7.
[2012]
8.
[2012]
9.
[2010]
10.
[2010]
Semiconductors
1.
[2015]
(a) 8 10^18 MeV (b) 8 10^16 MeV
(c) 4 10^18 MeV (d) 4 10^16 MeV
The half life of a particle of mass 1.6 10 ^26 kg is 6.9
s and a stream of such particles is travelling with
the kinetic energy of a particle being 0.05 eV. The
fraction of particles which will decay when they
travel a distance of 1 m is
(a) 0.1 (b) 0.01 (c) 0.001 (d) 0.0001
The binding energy per nucleon of 5 B^10 is 8.0 MeV
and that of 5 B^11 is 7.5 MeV. The energy required to
remove a neutron from 5 B^11 is (mass of electron
and proton are 9.11 10 and1.67 10 , ^31 ^27 kg
respectively)
(a) 2.5 MeV (b) 8.0 MeV
(c) 0.5 MeV (d) 7.5 MeV
A nuclear decay is possible if the mass of the parent
nucleus exceeds the total mass of the decay
particles. If M(A,Z) denotes the mass of a single
neutral atom of an element with mass number A and
atomic number Z, then the minimal condition that
the decay XZA YZA 1 ve
will occur is
(medenotes the mass of the particle and the
neutrino mass mvcan be neglected):
(a) M A Z M A Z( , ) ( , 1) me
(b) M A Z M A Z( , ) ( , 1)
(c) M A Z M A Z( , ) ( , 1) Zme
(d) M A Z M A Z( , ) ( , 1) me
A parent nucleus X is decaying into daughter
nucleus Y which in turn decays to Z. The half lives
of X and Y are 40000 years and 20 years respectively.
In a certain sample, it is found that the number of Y
nuclei hardly changes with time. If the number of X
nuclei in the sample is 4 10 ,^20 the number of Y
nuclei present in it is
(a) 2 10^17 (b) 2 10^20
(c) 4 10^23 (d) 4 10^20
A radioactive nucleus A has a single decay mode
with half life A. Another radioactive nucleus B
has two decay modes 1 and 2. If decay mode 2
were absent, the half life of B would have been
2
A. If decay mode 1 were absent, the half life of B
would have been 3 ,A then the ratio
B
A
is
(a)
3
7
(b)
7
2
(c)
7
3
(d) 1
A nucleus has a half-life of 30 minutes. At 3 PM its
decay rate was measured as 120,000 counts/sec.
What will be the decay rate at 5 PM?
(a) 120,000 counts/sec
(b) 60,000 counts/sec
(c) 30,000 counts/sec
(d) 7,500 counts/sec
At timet 0 , a container has N 0 radioactive atoms
with a decay constant . In addition, numbers of
atoms of the same type are being added to the
container per unit time. How many atoms of this
type are there at t = T?
(a) 0
c
exp T N expT
(b) 0
c
exp T N exp T
(c) ^1 0
c
expT N expT
(d) 1 exp 0 exp
c
T N T
A donor atom in a semiconductor has a loosely
bound electron. The orbit of this electron is
considerably affected by the semiconductor
material but behaves in many ways like an electron
orbiting a hydrogen nucleus. Given that the
electron has an effective mass of 0.07me, (where
meis mass of the free electron) and the space in
which it moves has a permittivity 13 , 0 then the
radius of the electron’s lowermost energy orbit will
be close to (The Bohr radius of the hydrogen atom
is 0.53Å)
(a) 0.53Å (b) 243Å (c)10Å (d) 100Å
