A monochromatic source of light operating at 200 W emits 4 × 10²⁰ photons per second. Find the wavelength of light.

400 mm
200 nm
4× 10^–10 Å
None of these

Solution

In an electron gun the control grid is given a negative potential relative to cathode in order to

decelerate electrons
repel electrons and thus to control the number of electrons passing through it
to select electrons of same velocity and to converge them along the axis.
to decrease the kinetic energy of electrons

The de-Broglie wavelength of a neutron at 927°C is λ.What will be its wavelength at 27 °C ?

^λ⁄₂
λ
2λ
4λ

Solution

An X-ray tube with Cu target is operated at 25 kV. The glancing angle for a NaCl. Crystal for the Cu k_α line is 15.8°.Find the wavelength of this line.(d for NaCl = 2.82 Å, h = 6.62 × 10^–27erg-sec)

3.06 Å
1.53 Å
0.75 Å
None of these

Solution

According to Bragg’s law,⇒ 2d sin θ = nλ,

n = 1 for first order

⇒ 2 × 2.82 sin 15.8 = λ ⇒ λ = 5.64 × 0.2723 = 1.53 Å

When X-rays of wavelength 0.5 Å would be transmitted by an aluminium tube of thickness 7 mm, its intensity remains one-fourth. The attenuation coefficient of aluminium for these X-rays is

0.188 mm^–1
0.189 mm^–1
0.198 mm^–1
None of these

Solution

What is the energy of k_αX-ray photon of copper (Z = 29) ?

7.99 keV
8.29 keV
8.25 keV
7.19 keV

Solution

E(k_α) = 10.2 (Z – 1)₂ eV
= 10.2 × 28₂
= 10.2 × 784
= 7.997 keV = 8 KeV

Which metal will be suitable for a photoelectric cell using light of wavelength 4000 Å. The work functions of sodium and copper are respectively 2.0 eV and 4.0 eV.

Sodium
Copper
Both
None of these

Solution

In an electron gun, the potential difference between the filament and plate is 3000 V.What will be the velocity of electron emitting from the gun?

3 × 10⁸m/s
3.18 × 10⁷m/s
3.52× 10⁷m/s
3.26 × 10⁷m/s

Solution

When the speed of electrons increase, then the value of its specific charge

increases
decreases
ramainsunchanged
increases upto some velocity and then begins to decrease

Solution

Here the velocity of electron increases, so as per Einstein’s equation mass of the electron increases,hence the specific charge ^e⁄_m decreases.

A steel ball of mass m is moving with a kinetic energy K. The de-Broglie wavelength associated with the ball is

\(\frac{h}{2mK}\)
\(\sqrt{\frac{h}{2mK}}\)
\(\frac{h}{\sqrt{2mK}}\)
meaningless

Solution

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