The wavenumber of a photon in the Brackett series of a hydrogen atom is \(\frac{9}{400}R.\) What is the quantum number of the electron that has transited from the orbit?
1. \(5\)
2. \(6\)
3. \(4\)
4. \(7\)

In an experiment to determine the e/m value for an electron using Thomson's method the electrostatic deflection plates were 0.01 m apart and had a potential difference of 200 volts applied. Then the electric field strength between the plates is 

1. $1\times {10}^4 V/m$ 

2. $2\times {10}^4 V/m$

3. $4\times {10}^4 V/m$ 

4. $5\times {10}^5 V/m$

To explain his theory, Bohr used

1. conservation of linear momentum

2. conservation of angular momentum

3. conservation of quantum  frequency

4. conservation of energy

Bragg's law for X-rays is:

1. dsin$\theta$ = 2n$\lambda$ 

2. 2dsin$\theta$ = n$\lambda$

3. nsin$\theta$ = 2$\lambda$d

4. None of these

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. $\frac{cV}{eh}$

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

which of the following is positively charged?

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

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

3.  $\mathrm{\gamma }-\mathrm{rays}$

4.  $\mathrm{X}-\mathrm{rays}$

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