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MCQ on Modern Physics for Students
The impurity atoms with which pure silicon may be doped to make it a p-type semiconductor are those of
(a) phosphorus
(b) boron
(c) antimony
(d) aluminum
Option b – boron
The electrical conductivity of pure germanium can be increased by
(a) increasing the temperature
(b) doping acceptor impurities
(c) doping donor impurities
(d) all of the above
Option d – all of the above
A semiconductor is doped with a donor impurity then
(a) the hole concentration increases
(b) the hole concentration decreases
(c) the electron concentration increases
(d) the electron concentration decreases
Option b – the hole concentration decreases
According to Bohr’s model of hydrogen atom
(a) the linear velocity of the electron is quantized.
(b) the angular velocity of the electron is quantized.
(c) the linear momentum of the electron is quantized.
(d) the angular momentum of the electron is quantized.
Option d – the angular momentum of the electron is quantized
Electric conduction in a semiconductor takes place due to
(a) electrons only
(b) holes only
(c) both electrons and holes
Option c – both electrons and holes
In a semiconductor
(a) there are no free electrons at 0 K
(b) there are no free electrons at any temperature
(c) the number of free electrons increases with the temperature
(d) the number of free electrons is less than that in a conductor
Option a – there are no free electrons at 0 K
A p-type semiconductor is
(a) positively charged.
(b) negatively charged
(c) uncharged
(d) uncharged at 0K but charged at higher temperatures
Option a – positively charged
Forward biasing is that in which applied voltage
(a) increases the potential barrier
(b) cancels the potential barrier
(c) is equal to 1.5 volts
(d) None of these
Option b – cancels the potential barrier
In the V-I characteristic of a p-n junction, reverse biasing results in
(a) leakage current
(b) the current barrier across the junction increases
(c) no flow of current
(d) large current
Option a – leakage current
Zener diode is used for
(a) amplification
(b) rectification
(c) stabilization
(d) all of the above
Option c – stabilization
The minimum energy required to eject an electron, from the metal surface is called
(a) atomic energy
(b) mechanical energy
(c) electrical energy
(d) workfunction
Option d – workfunction
X-rays are
(a) a stream of electrons
(b) a stream of positively charged particles
(c) electromagnetic radiations of high frequency
(d) a stream of unchanged particles
Option c – electromagnetic radiations of high frequency
The majority of charge carriers in a p-type semiconductor are
(a) free electrons
(b) conduction electrons
(c) ions
(d) holes
Option d – holes
The ionization energy of hydrogen atom in the ground state is
(a) 13.6 MeV
(b) 13.6 eV
(c) 13.6 Joule
(d) Zero
Option b – 13.6 eV
Which of the following planet is called the red planet?
(a) Mars
(b) Jupiter
(c) Saturn
(d) Uranus
Option a – Mars
The drift current in a p-n junction is
(a) from the n-side to the p-side
(b) from the p-side to the n-side
(c) from the n-side to the p-side if the junction is forward-biased and in the opposite direction if it is reverse biased
(d) from the p-side to the n-side if the junction is forward-biased and in the opposite direction if it is reverse-biased
Option a – from the n-side to the p-side
The diffusion current in a p-n junction is greater than the drift current in magnitude
(a) if the junction is forward-biased
(b) if the junction is reverse-biased
(c) if the junction is unbiased
(d) in no case
Option a – if the junction is forward-biased
In a p-type semiconductor, the acceptor valence band is
(a) close to the valence band of the host crystal
(b) close to the conduction band of the host crystal
(c) below is the conduction band of the host crystal
(d) above the conduction band of the host crystal
Option a – close to the valence band of the host crystal
In an n-type semiconductor, the donor valence band is
(a) above the conduction band of the host crystal
(b) close to the valence band of the host crystal
(c) close to the conduction band of the host crystal
(d) below is the valence band of the host crystal
Option c – close to the conduction band of the host crystal
In semiconductors, at room temperature
(a) the conduction band is completely empty
(b) the valence band is partially empty and the conduction band is partially filled
(c) the valence band is completely filled and the conduction band is partially filled
(d) the valence band is completely filled
Option c – the valence band is completely filled and the conduction band is partially filled
The diffusion current in a p-n junction is
(a) from the n-side to the p-side
(b) from the p-side to the n-side
(c) from the n-side to the p-side if the junction is forward-biased and in the opposite direction if it is reverse biased
(d) from the p-side to the n-side if the junction is forward-biased and in the opposite direction if it is reverse biased
Option b – from the p-side to the n-side
If the two ends of a p-n junction are joined by a wire
(a) there will not be a steady current in the circuit
(b) there will be a steady current from the n-side to the p-side
(c) there will be a steady current from the p-side to the n-side
(d) there may or may not be a current depending upon the resistance of the connecting wire
Option a – there will not be a steady current in the circuit
What is the resistivity of a pure semiconductor at absolute zero? ( MCQs on Modern Physics )
(a) Zero
(b) Infinity
(c) Same as that of conductors at room temperature
(d) Same as that of insulators at room temperature
Option b – Infinity
A photon is a/an
(a) quantum of light
(b) quantum of matter
(c) positively charged particle
(d) an instrument for measuring light intensity
Option a – quantum of light
Of the following properties, the photon does not possess
(a) rest mass
(b) momentum
(c) energy
(d) frequency
Option a – rest mass
A photon will have less energy if its
(a) amplitude is higher
(b) frequency is higher
(c) wavelength is longer
(d) wavelength is shorter
Option c – wavelength is longer
A photoelectric cell converts
(a) light energy into heat energy
(b) light energy to sound energy
(c) light energy into electric energy
(d) electric energy into light energy
Option c – light energy into electric energy
Light of a particular frequency v is incident on a metal surface. When the intensity of incident radiation is increased, the photoelectric current
(a) decreases
(b) increases
(c) remains unchanged
(d) sometimes increases and sometimes decreases
Option b – increases
The photoelectric effect is based on the law of conservation of
(a) momentum
(b) energy
(c) angular momentum
(d) mass
Option b – energy
As the intensity of incident light increases
(a) photoelectric current increases
(b) K.E. of emitted photoelectrons increases
(c) photoelectric current decreases
(d) K.E. of emitted photoelectrons decreases
Option a – photoelectric current increases
The photoelectrons emitted from a metal surface are such that their velocity
(a) is zero for all
(b) is the same for all
(c) lies between zero and infinity
(d) lies between zero and a finite maximum
Option d – lies between zero and a finite maximum
In which of the following, the emission of electrons does not take place?
(a) Thermionic emission
(b) X-rays emission
(c) Photoelectric emission
(d) Secondary emission
Option b – X-rays emission
According to Rutherford’s atomic model, the electrons inside the atom are
(a) stationary
(b) not stationary
(c) centralized
(d) None of these
Option b – not stationary
According to classical theory, the circular path of an electron in the Rutherford atom is
(a) spiral
(b) circular
(c) parabolic
(d) straight line
Option a – spiral
Electrons in the atom are held to the nucleus by
(a) coulomb’s force
(b) nuclear force
(c) Vander Waal’s force
(d) gravitational force
Option a – coulomb’s force
Which of the following shows the particle nature of light?
(a) Refraction
(b) Interference
(c) Polarization
(d) Photoelectric effect
Option d – Photoelectric effect
A strong argument for the particle nature of cathode rays is that they
(a) produce fluorescence
(b) travel through a vacuum
(c) get deflected by electric and magnetic fields
(d) cast shadow
Option c – get deflected by electric and magnetic fields
In the case of electrons and photons having the same wavelength. What is the same for them?
(a) Energy
(b) Velocity
(c) Momentum
(d) Angular momentum
Option c – Momentum
The best metal to be used for photoemission is
(a) potassium
(b) sodium
(c) cesium
(d) lithium
Option c – cesium
The phenomenon best supports the theory that matter has a wave nature
(a) electron momentum
(b) electron diffraction
(c) photon momentum
(d) photon diffraction
Option b – electron diffraction
G..P. Thomson experimentally confirmed the existence of matter waves through the phenomena
(a) diffraction
(b) refraction
(c) polarization
(d) scattering
Option b – refraction
In the Davison-Germer experiment, an electron beam is an incident on a crystal. The reflected beam consists of
(a) photons
(b) protons
(c) x-rays
(d) electrons
Option d – electrons
The specific charge for cathode rays is
(a) constant
(b) variable
(c) dependent upon the material of the cathode
(d) dependent upon the nature of the gas in the discharge tube
Option a – constant
Cathode rays are made to pass between the poles of a magnet perpendicular to the axis, the effect of the magnetic field is
(a) to increase the velocity of rays
(b) to deflect them toward the north pole
(c) to deflect them toward the south pole
(d) to deflect them upwards above the plane of the paper
Option d – to deflect them upwards above the plane of the paper
A ray of light, when refracted, undergoes a change in velocity. In this context, which of the following statements is correct?
(a) Velocity increases as the ray passes from a rarer to a denser medium.
(b) Velocity decreases as the ray passes from a denser to a rarer medium.
(c) Velocity decreases as the ray passes from a rarer to a denser medium.
(d) Change of velocity does not depend on the nature of the medium.
Option c – Velocity decreases as the ray passes from a rarer to a denser medium
An object is placed at the center of curvature of a concave mirror with a focal length of 16 cm. If the object is shifted by 8 cm towards the focus, then the nature of the image would be
(a) real and magnified.
(b) virtual and magnified.
(c) real and reduced.
(d) virtual and reduced.
Option a – real and magnified
Magnification is
(a) the actual size of the specimen/observed size.
(b) observed size of the specimen/actual size.
(c) the actual size of the specimen – observed size.
(d) observed size of the specimen/actual size.
Option b – observed size of the specimen/actual size
When light passes from one medium to another, the phenomenon of change in its direction is called ….
(a) Refraction
(b) Diffraction
(c) Propagation
(d) No option is correct
Option a – Refraction
When a ray of light travels from a denser medium to a rarer medium, it bends
(a) toward the normal and slows down.
(b) away from the normal and speeds up.
(c) away from the normal and slows down.
(d) towards the normal and speeds up.
Option b – away from the normal and speeds up
When a ray of light enters a glass slab, then
(a) only the frequency changes.
(b) frequency and velocity change.
(c) frequency does not change.
(d) frequency and wavelength change.
Option c – frequency does not change
Specific gravity is defined as the ratio of
(a) the density of the substance to the density of water.
(b) density of the substance to the density of water at 0°C.
(c) density of water at 4°C to the density of the substance.
(d) density of the substance to the density of water at 4°C.
Option d – density of the substance to the density of water at 4°C
A deep-sea diver may hurt his eardrum during diving because of
(a) lack of oxygen
(b) high atmospheric pressure
(c) high water pressure
(d) All of the above
Option c – high water pressure
Which one of the following devices is used to measure atmospheric pressure?
(a) Ammeter
(b) Barometer
(c) Potentiometer
(d) Lactometer
Option b – Barometer
The density of water is 1 g/cc. This is strictly valid at
(a) 0°C
(b) 4°C
(c) 25°C
(d) 100°C
Option b – 4°C
The density of water is
(a) maximum at 0°C
(b) minimum at 0°C
(c) maximum at 4°C
(d) minimum at -4°C
Option c – maximum at 4°C
Line spectrum is obtained whenever the incandescent vapors at low pressure of the excited substance are in their
(a) atomic state
(b) molecular state
(c) nuclear state
(d) None of these
Option a – atomic state
Which of the following statements are true regarding Bohr’s model of the hydrogen atom? (I) Orbiting speed of the electron decreases as it shifts to discrete orbits away from the nucleus (II) Radii of allowed orbits of the electron are proportional to the principal quantum number (III) Frequency with which electrons orbit around the nucleus in discrete orbits is inversely proportional to the cube of principal quantum number (IV) Binding force with which the electron is bound to the nucleus increases as it shifts to outer orbits Select the correct answer using the codes given below. Codes :
(a) I and II
(b) II and IV
(c) I, II, and III
(d) II, III, and IV
Option a – I and II
Which of the following series in the spectrum of hydrogen atoms lies in the visible region of the electromagnetic spectrum?
(a) Paschen series
(b) Balmer series
(c) Lyman series
(d) Brackett series
Option b – Balmer series
Electron emission from a metallic surface by the application of light is known as
(a) Thermionic emission
(b) Photoelectric emission
(c) High-field emission
(d) Auto electronic emission
Option b – Photoelectric emission
If the potential difference applied to an X-ray tube is doubled while keeping the separation between the filament and the target as same, what will happen to the cutoff wavelength?
(a) Will remain the same
(b) Will be doubled
(c) Will be halved
(d) Will be four times the original wavelength
Option c – Will be halved
As one considers orbits with higher values of n in a hydrogen atom, the electric potential energy of the atom
(a) decreases
(b) increases
(c) remains the same
(d) does not increase
Option b – increases
The wavelength of characteristic X-rays depends upon
(a) the temperature of the target
(b) the size of the target
(c) the atomic number of the target
(d) the mass of the target
Option c – the atomic number of the target
White X-rays are called white due to the fact that
(a) they are electromagnetic radiations having nature the same as that of white light.
(b) they are produced most abundantly in X-ray tubes.
(c) they have a continuous wavelength range.
(d) they can be converted to visible light using coated screens and photographic plates are affected by them just like light.
Option c – they have a continuous wavelength range
When a hydrogen atom is raised from the ground state to an excited state
(a) P.E. increases and K.E. decreases
(b) P.E. decreases and K.E. increases
(c) Both energy (K.E. and P.E.) increases
(d) Both K.E. and P.E. decreases
Option a – P.E. increases and K.E. decreases
As the quantum number increases, the difference in energy between consecutive energy levels
(a) remains the same
(b) increases
(c) decreases
(d) sometimes increases and sometimes decreases.
Option c – decreases
The photoelectric effect can be understood on the basis of
(a) wave theory of light only
(b) electromagnetic theory of light only
(c) quantum theory of light only
(d) None of these
Option c – quantum theory of light only
When light is incident on a metal surface the maximum kinetic energy of emitted electrons
(a) vary with the intensity of light
(b) varies with the frequency of light
(c) varies with the speed of light
(d) varies irregularly
Option b – varies with the frequency of light
A photo-sensitive metal is not emitting photo-electrons when irradiated. It will do so when the threshold is crossed. To cross the threshold we need to increase
(a) intensity
(b) frequency
(c) wavelength
(d) None of these
Option b – frequency
The work function for the photoelectric effect
(a) is different for different metals
(b) is the same for all metals
(c) depends upon the intensity of incident light
(d) depends upon the frequency of incident light
Option a – is different for different metals
In the photoelectric effect, electrons are emitted
(a) at a rate that is proportional to the amplitude of the incident radiation
(b) with a maximum velocity proportional to the frequency of the incident radiation
(c) at a rate that is independent of the emitter
(d) only if the frequency of the incident radiations is above a certain threshold value
Option d – only if the frequency of the incident radiations is above a certain threshold value
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