The space between the proton and the electron in a hydrogen atom is:

Which of the following is the radius of the first orbit of $He^{+}$ (in $pm$)?

In astronomical observations,signals observed from the distant stars are generally weak. If the photon detector receives a total of $3.15 \times 10^{-18} \, J$ from the radiations of $600 \, nm$,calculate the number of photons received by the detector.

If the speed of an electron in the Bohr's first orbit of a hydrogen atom is $x$,the speed of the electron in the third Bohr's orbit is:

$A$ $100 \, W$ bulb emits monochromatic light of wavelength $400 \, nm$. Calculate the number of photons emitted per second by the bulb.

Alpha-particles that come closer to the nucleus: