Bohr's postulate is based on _______________.

(a)

conservation of linear momentum

(b)

quantisation of angular momentum

(c)

conservation of quantum frequency

(d)

none of these

The circumference of an electron's orbit of radius r must be an integral multiple of de Broglie wavelength that is ________________.

(a)

0.529 nl

(b)

\(\sqrt nλ\)

(c)

13.61

(d)

2ㅠr = nλ

The ground state energy of a hydrogen atom is 13.6 eV. The energy needed to ionize H₂ atom from its second excited state ______________.

(a)

1.51 eV

(b)

3.4 eV

(c)

13.6 eV

(d)

none

In terms of Bohr radius a₀, the radius of the third Bohr orbit of a hydrogen atom is given by ______________.

(a)

8a_o

(b)

9a_o

(c)

6a_o

(d)

\(\sqrt 3\) a_o

The ionization energy of hydrogen atom is -13.6e V. The energy corresponding to a transition between 3rd and 4th orbit is ______________.

(a)

3.40 eV

(b)

1.51 eV

(c)

0.85 eV

(d)

0.66 eV

The total energy of electrons in the ground state of a hydrogen atom is -13.6 eV. The k.E of an electron in the first excited state is ____________.

(a)

6.8 eV

(b)

13.6 eV

(c)

1.7 eV

(d)

3.4 eV

An alpha nucleus of energy 1/2 mv² bombards a heavy nuclear target of charge Ze. Then the distance of the closest approach for the alpha nucleus will be proportional to ____________.

(a)

v²

(b)

\(\frac{1}{m}\)

(c)

\(\frac{1}{v^$}\)

(d)

\(\frac{1}{Ze}\)

An oil drop carrying a charge q has a mass of m kg. It is falling freely in the air with terminal speed v. The electric field required to make the drop move upwards with the same speed is ______________.

(a)

\(\frac{mg}{q}\)

(b)

\(\frac{2mg}{q}\)

(c)

\(\frac{mgv}{q^2}\)

(d)

\(\frac{2mgv}{q}\)

Millikan's oil drop experiment established that is ____________.

(a)

electric charge depends on velocity

(b)

electric charge is quantised

(c)

electron has wave nature

(d)

electron has particle nature

An a-particle of energy 10 meV is scattered through 180^o by a fixed uranium nucleus. The distance of the closest approach is of the order of _____________.

(a)

1Å

(b)

10^-10 cm

(c)

10^-12 cm

(d)

10^-15 cm

The fig. represents the observed intensity of X-rays emitted by an X-ray tube as a function of wavelength. The sharp peaks A and B denote ____________.
 

(a)

continuous spectrum

(b)

band spectrum

(c)

characteristic spectrum

(d)

white radiations

The minimum wavelength of the X-rays produced by electrons accelerated through a potential difference of V volts is directly proportional to _____________.

(a)

\(\frac { 1 }{ \sqrt { V } } \)

(b)

\(\frac { 1 }{ V } \)

(c)

\(\sqrt { V } \)

(d)

V²

According to to Bohr, the relation between principal quantum number (n) and radius of the orbit (r) is _____________.

(a)

r α \(\frac1n\)

(b)

r α \(\frac{1}{n^2}\)

(c)

r α n

(d)

r α n²

The energy of the ground state of hydrogen is -13.6 eV. The energy of the first excited state is _____________.

(a)

-27.2 eV

(b)

-52.4 eV

(c)

-3.4 eV

(d)

-6.8 eV

When hydrogen atom is in its first excited level, its radius is __________ of the Bohr radius.

(a)

twice

(b)

same

(c)

half

(d)

four times