The number of photons of light with a wavelength of 4000 pm that provide 1J of energy would be: 

$1.$ $2.01$ $\times$ ${10}^{16}$
$2.$ $2.01$ $\times$ ${10}^{19}$
$3.$ $4.14$ $\times$ ${10}^{23}$
$4.$ $2.14$ $\times$ ${10}^{21}$

Electromagnetic radiation of wavelength 242 nm is just sufficient to ionise sodium atom. The ionisation energy of sodium in kJ mol^-1 is -

1. 494

2. 4.94

3. 516

4. 0.50

A 25-watt bulb emits monochromatic yellow light with a wave length of 0.57µm. The rate of emission of quanta per second would be :

1. 7.17×10^-19 s^-1

2. 4.13×10¹⁶s-¹

3 . 7.17×10¹⁹ s^-1

4 . 1.26 ×10²⁰s^-1
${\mathrm{}}^{}$

A nitrogen laser produces radiation at a wavelength of 337.1 nm. If the number of
photons emitted is 5.6 × 10²⁴, the power of the laser is:

$\mathrm{}$$1.$ $4.56$ $\times$ ${10}^7$ $\mathrm{J}$
$2.$ $3.33$ $\times$ ${10}^6$ $\mathrm{J}$
$3.$ $1.29$ $\times$ ${10}^6$ $\mathrm{J}$
$4.$ $9.17$ $\times$ ${10}^5$ $\mathrm{J}$

If the photon detector receives a total of 3.15$\times {10}^{-18}$ J from the radiation of 600 nm,
the number of photons received by the detector would be: 

$1.$ ${10}^2$
$2.$ $10$
$3.$ $50$
$4.$ $20$

A radiation source emitted  2.5 × 10¹⁵ photons in 2 nanoseconds. Energy of the source is -

$1.$ $8.28$ $\times$ ${10}^{-10}$ $\mathrm{J}$
$2.$ $8.24$ $\times$ ${10}^{10}$ $\mathrm{J}$
$3.$ $7.12$ $\times$ ${10}^{-11}$ $\mathrm{J}$
$4.$ $2.12$ $\times$ ${10}^{}$ $10$ $\mathrm{J}$

The wavelength of the light emitted when the electron returns to the ground state in the H atom, from n = 5 to n = 1, would be: (The ground-state electron energy is –2.18 × 10^-18 j) 
1. Wavelength = 9.498 x 10^-8 km
2. Wavelength = 12.498 x 10^-8 m
3. Wavelength = 9.498 x 10^-8 m
4. Wavelength = 9.498 x 10^-8 cm

The neon gas emits radiation of 616 nm. The number of quanta that are present in 2 J of energy is:

$1.$ $6.2$ $\times$ ${10}^{-18}$
$2.$ $5.6$ $\times$ ${10}^{17}$
$3.$ $6.2$ $\times$ ${10}^{18}$
$4.$ $32.2$ $\times$ ${10}^{-20}$
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