40 past paper MCQs from Physics unit 15, Atomic Spectra, across 1 topic. They are arranged topic by topic; bigger topics show a sample here and link to their full set and to study notes. Tap “Show answer” for the correct option and a short solution.
1.The line spectrum of the hydrogen atom contains spectral lines in the region of: (MDCAT 2022)
Correct answer: (d) all of these
The Lyman series is ultraviolet, the Balmer series visible and the Paschen and later series infrared.
2.The speed of an electron in the first Bohr orbit is: (MDCAT 2022)
Correct answer: (b) $2.19\times10^{6}\ \mathrm{m\,s^{-1}}$
The first orbit speed is about $2.19\times10^{6}\ \mathrm{m\,s^{-1}}$, roughly one hundredth of the speed of light.
3.Which of the following is the longest wavelength available for the Paschen series? (MDCAT 2023)
Correct answer: (c) $1.87\times10^{-6}\ \mathrm{m}$
The longest wavelength of a series comes from its smallest energy step, $n=4\to3$, and is about $1.87\times10^{-6}$ m, in the infrared.
4.Which series falls in the ultraviolet region? (MDCAT 2024)
Correct answer: (a) Lyman
The Lyman series ends on $n=1$ and its photons are the most energetic, in the ultraviolet.
5.The potential through which an electron should be accelerated so that on collision it can lift an electron in an atom from its ground state to some higher state is known as the: (MDCAT 2024)
Correct answer: (b) excitation potential
Raising an electron to a higher level rather than removing it altogether needs the excitation potential.
6.Which of the following X-rays has the largest intensity? (UHS MDCAT 2017)
Correct answer: (a) $K_{\alpha}$ X-ray
The jump from the nearest shell is the most probable one, so the $K_{\alpha}$ line is the strongest.
7.The hardest photon coming out of a Coolidge tube belongs to: (UHS MDCAT 2017)
Correct answer: (b) continuous X-rays
The most energetic photon is the one emitted when an electron loses all its energy in a single stop, which is the short wavelength limit of the continuous spectrum.
8.The Balmer series of hydrogen spectrum appears in the (UHS MDCAT 2025)
Correct answer: (d) Visible region
The Balmer lines end on the second level and fall in the visible part of the spectrum.
9.In hydrogen spectrum, the Brackett series lies in (KMU MDCAT 2025)
Correct answer: (c) Infrared region
The Brackett lines end on the fourth level, and their photons fall in the infrared.
10.Which of the following spectrum is produced when atoms are in the gaseous state? (NUMS MDCAT 2025)
Correct answer: (c) Line spectrum
Free atoms of a gas emit at sharply defined frequencies, so the spectrum is a set of lines.
11.Quantized momentum was explained by: (NUMS MDCAT 2025)
Correct answer: (b) Bohr
Bohr postulated that the angular momentum of the orbiting electron is a whole multiple of $h/2\pi$.
12.The spectra obtained by absorption or emission of radiation by atoms of the gas: (NUMS MDCAT 2025)
Correct answer: (a) Atomic spectra
Spectra given out or taken up by free atoms are atomic spectra.
13.Two spectral lines in the Hydrogen atom spectrum are close together. This likely means: (SZABMU MDCAT 2025)
Correct answer: (b) The energy difference is small
Photon energy sets the frequency, so lines close together come from levels close in energy.
14.Which series falls in ultra violet region? (UHS MDCAT 2024)
Correct answer: (a) Lyman
The Lyman lines end on the ground level, and their photons are ultraviolet.
15.The potential through which an electron should be accelerated , so that,on collision it can lift the electron in the atom from its ground state to some higher state is known as (UHS MDCAT 2024)
Correct answer: (b) Excitation potential
The potential that just lifts an electron to a higher level is the excitation potential.
16.Which of the following regarding X Rays is INCORRECT (UHS MDCAT 2024)
Correct answer: (a) Have higher wavelength than visible light
X-rays have a far shorter wavelength than visible light, which is why they carry so much energy.
17.If an electron in the hydrogen atom jumps from second to first orbit, the emitted radiation has a wavelength of? (KMU MDCAT 2024)
Correct answer: (a) 4/3RH
$1/\lambda=R(1-1/4)=3R/4$, so the wavelength is $4/3R$.
18.Q.172 The line spectrum of hydrogen atom contains the spectral lines in the region of: (UHS MDCAT 2023)
Correct answer: (d) all of these
The Lyman lines are ultraviolet, the Balmer visible, and the rest infrared.
19.Q.173 The speed of electron in the first Bohr orbit is: (UHS MDCAT 2023)
Correct answer: (a) 2.19 x 10^6 ms^-1
In the first Bohr orbit the electron moves at about $2.19\times10^6\,\mathrm{m\,s^{-1}}$.
20.Which one of the following series lies in the ultraviolet region? (SZABMU MDCAT 2023)
Correct answer: (c) Lyman series
The Lyman lines end on the ground level and lie in the ultraviolet.
21.Which x-ray photon will have longest wavelength? (SZABMU MDCAT 2023)
Correct answer: (a) Kα
The K alpha line comes from the smallest energy drop of the K series, so its wavelength is the longest.
22.The Balmer series of hydrogen is important because it: (UHS MDCAT 2023)
Correct answer: (c) Is in the visible region
The Balmer lines end on the second level, and they are the ones the eye can see.
23.X-ray is the reverse process of: (PMC MDCAT 2022)
Correct answer: (c) Photoelectric effect
In the photoelectric effect a photon frees an electron; in X-ray production a stopped electron makes a photon.
24.Where does the energy lost by fast moving electron go: (PMC MDCAT 2022)
Correct answer: (a) Appears as photon
A fast electron stopped suddenly gives up its energy as an X-ray photon.
25.Lasers are produced by: (PMC MDCAT 2022)
Correct answer: (a) Stimulated emission
A laser works by stimulated emission, which is what makes its light coherent.
26.Bright Lines in pattern shows: (PMC MDCAT 2022)
Correct answer: (b) Emission
Bright lines are made by atoms giving out photons, that is by emission.
27.When electron absorbs a photon and jumps to higher states it is called: (PMC MDCAT 2022)
Correct answer: (b) Excitation
Absorbing a photon lifts the electron to a higher level, which is excitation.
28.X rays are also known as: (PMC MDCAT 2022)
Correct answer: (c) High energy invisible photons
X-rays are photons far beyond the violet in energy, and the eye cannot see them.
29.Spectral lines is like a —– of absorbed or emission energy in a spectrum: (PMC MDCAT 2022)
Correct answer: (b) Fingerprint Pattern
Every element has its own set of lines, so the spectrum identifies it as a fingerprint would.
30.The source of x-rays generation is: (PMC Practice 2021)
Correct answer: (a) Cu
A heavy metal target such as copper or tungsten stops the electrons and gives out X-rays.
31.The fast-moving electrons stopped by a heavy metallic target in an evacuated glass tube, give rise to the production of: (PMC Practice 2021)
Correct answer: (b) X-rays
Fast electrons stopped by a heavy target give out X-rays.
32.Which one of them is a type of emission? (PMC Practice 2021)
Correct answer: (c) Both Options A and B are correct
An atom may drop of itself, which is spontaneous emission, or be triggered by a passing photon, which is stimulated.
33.Which of the following series lies in the ultraviolet range: (PMC MDCAT 2020)
Correct answer: (c) Lyman series
The Lyman lines end on the ground level and lie in the ultraviolet.
34.The main difference between X rays and Y rays is: (PMC MDCAT 2020)
Correct answer: (d) Origin
X-rays come from the electron cloud and gamma rays from the nucleus; their wavelengths overlap.
35.The hardest photon coming out from a Coolidge tube belongs to: (UHS MDCAT 2017)
Correct answer: (a) Characteristic X-Rays
The hardest photons come from the sharp characteristic lines, where an inner shell vacancy is filled.
36.The continuous spectrum of X-ray is formed due to: (UHS MDCAT 2016)
Correct answer: (b) Bremsstrahlung X-ray
Electrons braked by the target give up energy in any amount, so the background is continuous.
37.The shadow of the bones in X-rays photographic film appears lighter than the surrounding flesh due to: (UHS MDCAT 2016)
Correct answer: (c) Bones absorb greater amount of X-rays
Bone contains calcium and absorbs the X-rays strongly, so less reaches the film behind it.
38.Wavelength of γ-rays is: (UHS MDCAT 2016)
Correct answer: (c) Shorter to the X-rays
Gamma rays come from the nucleus and carry more energy still, so their wavelength is the shorter.
39.The target of X-ray tube is made up of which metal? (UHS MDCAT 2016)
Correct answer: (d) Tungsten
Tungsten is used because it is dense and stands the heat.
40.The X-rays consists of: (UHS MDCAT 2016)
Correct answer: (d) High energy photons
X-rays are electromagnetic radiation, that is photons of high energy.