The longest and shortest wavelength of the Lyman series are (respectively)

1.  $1215 \stackrel{0}{\mathrm{A}}, 500 \stackrel{0}{\mathrm{A}}$

2.  $1215 \stackrel{0}{\mathrm{A}}, 912 \stackrel{0}{\mathrm{A}}$

3.  $912 \stackrel{0}{\mathrm{A}}, 500 \stackrel{0}{\mathrm{A}}$

4. $912 \stackrel{0}{\mathrm{A}}, 700 \stackrel{0}{\mathrm{A}}$

The frequency Of radiation emitted during the transition of an electron from a second excited state to a first excited state in H-atom is ${\mathrm{f}}_0.$ The frequency of the same transition emitted by a singly ionized He ion is

1.  $2{\mathrm{f}}_0$

2.  $4{\mathrm{f}}_0$

3.  $\frac{{\mathrm{f}}_0}{2}$

4.  $\frac{{\mathrm{f}}_0}{4}$

When the electron of a hydrogen-like atom jumps from a higher energy level to a lower energy level, then,

1.  the angular momentum of the electron remains constant.

2.  the kinetic energy of the electron increases.

3.  the wavelength of the de-Broglie wave associated with the motion of the electron increases.

4.  the potential energy increases.

The energy of a hydrogen atom in its ground state is —13.6 eV. The energy of the level corresponding to the quantum number n = 2 (first excited state) in the hydrogen atom is:

1. -2.72 eV

2. - 0.85 eV

3. -0.54 eV

4. — 3.4 eV

Magnetic moment due to the motion of the electron in ${\mathrm{n}}^{\mathrm{th}}$  energy state of a hydrogen atom is proportional to

1.  n

2.  ${\mathrm{n}}^0$

3.  ${\mathrm{n}}^5$

4.  ${\mathrm{n}}^3$

A X-ray tube operates at an accelerating potential of 20 kV. Which of the following wavelength will be absent in the continuous spectrum of X-rays?

1.  12 pm

2.  75 pm

3.  65 pm

4.  95 pm

which of the following is positively charged?

1.  $\mathrm{\alpha }-\mathrm{particles}$

2.  $\mathrm{\beta }-\mathrm{particles}$

3.  $\mathrm{\gamma }-\mathrm{rays}$

4.  $\mathrm{X}-\mathrm{rays}$

The wavelength of $K_{\alpha }$ X-rays for lead isotopes $P{b}^{208}, P{b}^{206}, P{b}^{204} are {\lambda }_1, {\lambda }_2 and {\lambda }_3$ respectively. Then

1. ${\lambda }_1={\lambda }_2>{\lambda }_3$   

2. ${\lambda }_1>{\lambda }_2>{\lambda }_3$

3. ${\lambda }_1<{\lambda }_2<{\lambda }_3$ 

4. ${\lambda }_2={\lambda }_1={\lambda }_3$

The graph between the square root of the frequency of a specific line of the characteristic spectrum of X-rays and the atomic number of the target will be:

1.
2.
3.
4.

The minimum wavelength of X-rays produced by electrons accelerated by a potential difference of V volt is equal to 

1. $\frac{eV}{hc}$ 

2. $\frac{eh}{cV}$ 

3. $\frac{hc}{eV}$ 

4. $\frac{cV}{eh}$