The Coolidge Tube

Q. The minimum wavelength of x-rays emitted from x-ray machine operating at an accelerating potential of V volts is

1. $\frac{hc}{eV}$
2. $\frac{Vc}{eh}$
3. $\frac{eh}{Vc}$
4. $\frac{eV}{hc}$

Q. In Young's double slit experiment, the wavelength of red light is $7800\mathring{A}$ and that of blue is $5200\mathring{A}.$ The value of $n$ for which $n^{th}$ bright band due to red light coincides with $(n+1{)}^{th}$ bright band due to blue light is-

1. $1$
2. $2$
3. $3$
4. $4$

Q. Which of the following wavelength will be absent from the X-ray spectrum if the X-ray tube is operated at 40, 000 V?

1. $0.2A^{\circ }$
2. $1.0A^{\circ }$
3. $2.0A^{\circ }$
4. $0.5A^{\circ }$

Q.

In Coolidge tube electrons were ejected by the cathode because of which method:

1. Photo electric emission

2. Corona discharge

3. All of the above.

4. Thermionic emission

Q. In Coolidge tube if $f$ and $\lambda$ represents the frequency and wavelength respectively of $K_{\alpha }$ line for a metal of atomic number $Z$, then identify the option(s) which represents a straight line.

1. $\sqrt{f}$ versus $Z$
2. $\frac{1}{\sqrt{\lambda }}$ versus $Z$
3. $f$ versus $Z$
4. $\lambda$ versus $Z$

Q. In terms of Rydberg's constant $R$, the wavenumber of first line of Balmer series is,

1. $R$
2. $3R$
3. $\frac{5R}{36}$
4. $\frac{8R}{9}$

Q. The cut off wavelength of continuous X-ray from two Coolidge tubes operating at 30 kV but using different target materials (molybdenum Z= 42 and tungsten Z = 74) are

1. $1\stackrel{\circ }{A},3\stackrel{\circ }{A}$
2. $0.3\stackrel{\circ }{A},0.2\stackrel{\circ }{A}$
3. $0.414\stackrel{\circ }{A},0.8\stackrel{\circ }{A}$
4. $0.414\stackrel{\circ }{A},0.414\stackrel{\circ }{A}$

Q. Which of the following wavelength will be absent from the X-ray spectrum if the X-ray tube is operated at 40, 000 V?

1. $0.2A^{\circ }$
2. $0.5A^{\circ }$
3. $1.0A^{\circ }$
4. $2.0A^{\circ }$

Q. The shortest wavelength of X-rays emitted from an X-ray tube depends on

1. The voltage applied to the tube
2. The current in tube
3. The nature of the gas in tube
4. The atomic number of the target material

Q.

Two discharge tubes have idential material structure and the same gas is filled in them. The length of one tube is 10 cm and that of the other tube is 20 cm. Sparking starts in both the tubes when th epotential difference between the cathode and the anode is 100 V. If the pressure in the shorter tube is 1.0 mm of mercury, what is the pressure in the longer tube?

Q. An optical fibre can offer a band width of _______.

1. $100GHz$
2. $100MHz$
3. $750MHz$
4. $250MHz$

Q.

Some important modifications were made to the Crooke's tube to make it a more efficient x ray source. Why was the coolant added to the anode plate?

1. None of the reasons stated here

2. Most of the kinetic energy of the electrons get converted into heat upon falling on the anode plate, turning it very hot.

3. The anode plate will radiate x rays more vigorously when the surface is cold

4. The liquid in the coolant increases the conductivity in the external circuit

Q. X-ray from a Coolidge tube is incident on a thin aluminium foil. The intensity of the X-ray transmitted by the foil is found to be I₀. The heating current is increased to increase the temperature of the filament. The intensity of the X-ray transmitted by the foil will be
(a) zero
(b) < I₀
(c) I₀
(d) > I₀

Q. Assertion :The rate of thermionic emission is less in an evacuated bulb as compared to one which is filled with inert gas at low pressure. Reason: An inert gas at low pressure ionises where as vacuum is the poorest conductor of electricity.

1. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
2. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
3. Assertion is correct but Reason is incorrect
4. Both Assertion and Reason are incorrect

Q.

The mean free path of electrons in th gas in a discharge tube is inversely proportional to the pressure inside it. The Crookes dark space occupies half the length of the discharge tube when the pressure is 0.02 mm of mercury. Estimate the pressure at which the dark space will fill the whole tube.

Q. How will the thermionic current vary if the filament current is increased?

Q. In X-ray spectrum wavelength $\lambda$ of line $K_a$ depends on atomic number $Z$ as

1. $\lambda \propto Z^2$
2. $\lambda \propto (Z-1{)}^2$
3. $\lambda \propto {\frac{1}{(Z-1)}}^2$
4. $\lambda \propto \frac{1}{(Z-1)}$

Q. When using high voltage to carry current over a large distance, wouldnt the heat loss be high too due to the equation P=V^2/R. Just like it is high for high values of I?

Q. By making applied voltage one fourth of the initial value in X- ray tube, cut-off wavelength for the continuous X- ray becomes

1. four times
2. one fourth times
3. two times
4. sixteen times

Q. Thermionic emitters can be classified into _________ and ________ .

1. direct LED and indirect LED
2. direct transistor and indirect transistor
3. directly heated thermionic emitter and indirectly heated thermionic emitter
4. directly heated emitter and indirectly heated emitter

Q.

The speed of EM wave is:

1. Same in all the media

2. Ultimate speed in nature

3. Very less as compared to the speed of light

4. Zero in vacuum