An oil drop carries a negative charge of −1.282 × 10⁻¹⁸ C. Calculate the number of excess electrons present on the oil drop.

1. Fifteen (15)

2. Eight (8)

3. Two (2)

4. Six (6)

An atom has a mass number of 81 and contains 31.7% more neutrons than protons. Which of the following represents the correct atomic symbol of the element?

$1.$ ${}_{35}{}^{81}\mathrm{Br}$
$2.$ ${}_{36}{}^{81}\mathrm{Br}$
$3.$ ${}_{35}{}^{79}\mathrm{Br}$
$4.$ ${}_{36}{}^{79}\mathrm{Br}$

An ion with mass number 37 possesses one unit of negative charge,the ion contains 11.1% more neutrons than the electrons. The symbol of the ion is-

$$\begin{gathered} 1.<mspace\; width="1em"></mspace>{}_{18}{}^{37}\mathrm{Cl} \\ 2.<mspace\; width="1em"></mspace>{}_{17}{}^{37}\mathrm{Cl} \\ 3.<mspace\; width="1em"></mspace>{}_{19}{}^{38}\mathrm{Cl} \\ 4.<mspace\; width="1em"></mspace>{}_{19}{}^{37}\mathrm{Cl} \end{gathered}$$

The wavelength of radiation emitted by a nitrogen laser is 337.1 nm. Calculate its power if the photon emission rate is 5.6 × 10²⁴ s⁻¹.

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

A photon detector receives a total energy of \(3.15 \times 10^{-18}\) J from radiation with a wavelength of 600 nm. How many photons are received by the detector?

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

Calculate the total energy associated with 2.5 × 10¹⁵ photons of radiation having a time period of 2 nanoseconds.

Emission transitions in the Paschen series end at orbit n = 3 and start from orbit n and can be represented as \(\mathrm v=3.29 \times 10^{15}(\mathrm{~Hz})\left(\frac{1}{3^2}- \frac{1}{\mathrm{n}^2}\right).\) The value of n if the transition is observed at 1285 nm is :

If the velocity of the electron is 1.6 × 10⁶ ${\mathrm{ms}}^{-1}$. Find the de-Broglie wavelength associated with this electron:

$1.$ $590$ $\mathrm{pm}$
$2.$ $455$ $\mathrm{pm}$
$3.$ $512$ $\mathrm{pm}$
$4.$ $401$ $\mathrm{pm}$

What is the velocity associated with a neutron that has a wavelength of 800 pm?

The velocity associated with a proton moving at a potential difference of 1000 V is 4.37 × 10⁵ ms^–1. If the hockey ball of mass 0.1 kg is moving with this velocity, then the wavelength associated with this velocity would be:

$1.$ $1.52$ $\times {10}^{-38}$ $\mathrm{m}$
$2.$ $2.54$ $\times$ ${10}^{-32}$ $\mathrm{m}$
$3.$ $1.52$ $\times$ ${10}^{-36}$ $\mathrm{m}$
$4.$ $3.19$ $\times$ ${10}^{-34}$ $\mathrm{m}$