250+ TOP MCQs on Wave Optics – Huygen’s Principle | Class12 Physics

Physics Multiple Choice Questions on “Wave Optics – Huygen’s Principle”.

1. Which among the following isn’t a suitable phenomenon to establish that light is wave motion?
a) Interference
b) Diffraction
c) Reflection
d) Polarization
Answer: c
Clarification: Light undergoes interference, diffraction, and polarization. These phenomena establish that light is a wave motion. Therefore, out of the options, reflection isn’t a suitable phenomenon to establish that light is wave motion.

2. The optical path of monochromatic light is the same if it travels 2 cm thickness of glass or 2.25 cm thickness of water. If the refractive index of water is 1.33, what is the refractive index of glass?
a) 2.5
b) 1.5
c) 3.5
d) 4.5
Answer: b
Clarification: Optical path = μ × Path in medium.
The optical path for glass = Optical path for water.
μg = (frac {(1.33 times 2.25)}{(2.0)})
μg = 1.50.

3. Identify the condition which is not necessary for two light waves to be coherent.
a) The two waves must be continuous
b) The two waves should be of the same frequency or wavelength
c) They should have a constant or zero phases difference
d) They two light sources should be narrow
Answer: d
Clarification: The essential conditions for two light waves to be coherent includes that the two waves must be continuous, the two waves should be of the same frequency or wavelength, and they should have a constant or zero phases difference. So, the unnecessary condition for two light waves to be coherent is the statement that the sources should be narrow.

4. The absolute refractive indices of glass and water are (frac {3}{2}) and (frac {4}{3}). Determine the ratio of the speeds of light in glass and water.
a) 5:7
b) 9:8
c) 7:5
d) 8:9
Answer: d
Clarification: ( frac {v_g}{v_w} = frac {mu_w}{mu_g})
(frac {v_g}{v_w} = frac {(frac {4}{3} )}{(frac {3}{2}) })
(frac {v_g}{v_w}) = 8:9

5. The refractive index of glass is 1.5 and that of water is 1.3, the speed of light in water is 2.25 × 108 m/s. What is the speed of light in glass?
a) 7.95 × 108 m/s
b) 9.95 × 108 m/s
c) 1.95 × 108 m/s
d) 3.95 × 108 m/s
Answer: c
Clarification: ( frac {v_g}{v_w} = frac {mu_w}{mu_g})
Vg = ((frac {mu_w}{mu_g})) × vw
(frac {v_g}{v_w} = ( frac {1.3}{1.5} ) ) × 2.25 × 108
(frac {v_g}{v_w}) = 1.95 × 108 m/s.

6. In Huygens’ theory, light waves are longitudinal and do not require a material medium for their propagation.
a) True
b) False
Answer: b
Clarification: In Huygens’ theory, light waves are longitudinal and require a material medium for their propagation. That is why, Huygens’ assumed the existence of an all-pervading hypothetical medium, called ether.

7. The speed of light in air is 3 × 108 m/s. If the refractive index of glass is 1.5, find the time taken by light to travel a distance of 10 cm in the glass.
a) 0.5 × 10-10 s
b) 5 × 10-10 s
c) 50 × 10-10 s
d) 500 × 10-10 s
Answer: b
Clarification: vg = (frac {c}{mu } = frac {(3 times 10^8)}{(1.5)}) = 2 × 108 m/s.
Time, t = (frac {Displacement}{v_g})
t = (frac {(10 times 10^{-2})}{(2 times 10^8)})
t = 5 × 10-10 s.

8. The speed of yellow light in a certain liquid is 2.4 × 108 m/s. Find the refractive index of the liquid.
a) 1.25
b) 5.55
c) 6.25
d) 12.25
Answer: a
Clarification: μ1 = (frac {c}{v_1})
μ1 = (frac {(3 times 10^8)}{(2.4 times 10^8) })
μ1 = 1.25.

250+ TOP MCQs on The Line Spectra of the Hydrogen Atom | Class12 Physics

Physics Assessment Questions for Class 12 on “The Line Spectra of the Hydrogen Atom”.

1. What causes spectral lines?
a) The transition of electrons between two energy levels
b) The transition of electrons between two wavelength ranges
c) Magnetic and electric field exiting in an atom
d) The transition of electrons from electric to magnetic field
Answer: a
Clarification: The observed spectral lines are caused by the transition of electrons between two energy levels in an atom. The emission spectrum of the hydrogen atom is divided into many spectral series, with wavelengths that are given by Rydberg’s formula.

2. How many spectral lines are there in the hydrogen spectrum?
a) Infinity
b) Zero
c) Multiple
d) One
Answer: c
Clarification: Even though hydrogen has only one electron in its outermost shell, it has multiple spectral lines. This is because hydrogen has many energy levels. When the electron excites from a lower level of energy into a higher level, then it releases a photon, and this photon is the one that appears as spectral lines.

3. Which theory explained that electrons revolved in circular orbits?
a) Einstein theory
b) Bohr theory
c) Rydberg theory
d) de – Broglie theory
Answer: b
Clarification: Niels Bohr explained the line spectrum of the hydrogen atom with the assumption that electrons revolved around an atom in circular orbits and that the orbit closer to the nucleus represented the ground state and the farther orbits represented the higher levels of energy.

4. Bohr’s model only works for hydrogen or helium.
a) True
b) False
Answer: a
Clarification: Yes, this is a true statement. Bohr’s model works only for elements like hydrogen because the model only considers the interactions between one electron and the nucleus. If there are more electrons, then they will repel the one electron, and this, in turn, will change its energy level.

5. When is hydrogen stable?
a) When the electron jumps to higher energy levels
b) When an electric field is introduced
c) When a magnetic field is introduced
d) When the electron is at its ground state
Answer: d
Clarification: The hydrogen atom is stable when the electron rests at the ground level of energy, i.e. when the principal quantum number, n = 1. In other words, when the electron is revolving in the first orbit around the nucleus, the hydrogen atom is stable.

6. Which of the following is found in the UV region of the spectrum?
a) Pfund series
b) Brackett series
c) Lyman series
d) Paschen series
Answer: c
Clarification: The transitions that end at the ground level, where the principal quantum number is one, are called the Lyman series. Here, the energies that are released are so large, and therefore, these spectral lines appear in the ultraviolet region of the spectrum.

7. How many spectral lines does hydrogen have?
a) Four
b) Three
c) Two
d) One
Answer: a
Clarification: Niels Bohr calculated the energies that a hydrogen atom would have in each of its energy levels, based on the wavelength of the spectral lines. Then he found out that there are four spectral lines for hydrogen, namely, Lyman, Balmer, Paschen, and Brackett series. The Lyman series lies in the UV region, whereas the Balmer series lies in the visible region, and the last two lie in the infrared region.

Physics Assessment Questions for Class 12,

250+ TOP MCQs on Coulomb’s Law | Class12 Physics

Physics Multiple Choice Questions on “Coulomb’s Law”.

1. Coulomb’s Law is valid for ______
a) Only point charge
b) For both point charge and distributed charge
c) Only distributed charges
d) Neither distributed nor point charge

Answer: a
Clarification: Coulomb’s Law explains the force between two point charges only. A distributed charge can be considered as the sum of infinite point charges and thus the force between two distributed charge systems can be explained.

2. Coulomb’s Law is valid for any distance between the particles.
a) False
b) True

Answer: a
Clarification: Coulomb’s Law is not valid for inter-atomic distance i.e. distance less than 10-15 m. Besides, if the distance between the two bodies is less than the size of any of the bodies, this law is also invalid. We can use this law only in all other cases.

3. Which one of the following is similar between electrostatic force and gravitational force?
a) Force can be attractive or repulsive
b) The force depends on the medium between the bodies
c) Both the forces are strong forces
d) Force is inversely proportional to the distance between the bodies

Answer: d
Clarification: Gravitational force cannot be repulsive and it is a very weak force. Gravitational force does not depend on the medium. But both the forces are inversely proportional to the distance between them.

4. Two 1 Coulomb charges are kept at 1m distance in air medium. Force of attraction or repulsion between them will be ________
a) 9*109 N
b) 1 dyne
c) 1 N
d) 3*103 N

Answer: a
Clarification: According to Coulomb’s Law, F=(frac {1}{4pi varepsilon_o }*frac {q_1q_2}{r^2}). And (frac {1}{4pi varepsilon_o}) = 9*109N in the SI system. In this case, q1=q2=1C and r=1m. Now substituting the values we get F=9*109N. Similarly, the electric field at a distance of 1m from a 1C charge is 9*109N/C.

5. Let B be the midpoint of AC. Two point charges Q are placed at A and C. What should be the value of charge placed at B so that the system remains at equilibrium?
a) –Q/2
b) –Q/4
c) +Q/2
d) +Q/4

Answer: b

6. 1 emu = __________ C
a) 10
b) 3*109
c) 4.8*10-10
d) 0.1

Answer: a
Clarification: 1 emu charge is equal to 10-coulomb charge while 1 coulomb is equal to 3*109 esu charge. Emu and C both are the units of charge and hence their conversion formula is necessary for many numerical problems.

7. If the force between two charges is 9N, what will be the force if the distance between them is doubled and both the charges are increased to √2 times?
a) 9N
b) 4.5N
c) 3N
d) 3.75N

Answer: b
Clarification: The force will be 9*(frac {sqrt2*sqrt2}{2^2}) N=4.5N because the force is proportional to the product of the two charges and inversely proportional to the square of the distance between them. Similarly, if the charges are the same but the distance is doubled, the force between them will be (frac {1}{4}) times the previous value.

8. Two charges q1, q2 exert some amount of force on each other. What will happen to the force on q1 if another charge q3 is brought close to them?
a) The force will increase
b) The force will decrease
c) The force remains the same
d) The force may increase or decrease depending on whether q3 is positive or negative

Answer: d
Clarification: If both the charges q1 and q2 are positive then they will repel each other. Now if the third charge q3 is also positive, the repulsive force will increase. But if q3 is negative, the repulsive force will be reduced by some amount due to the attractive force between q1 and q3.

9. Two negative charges are kept at a certain distance in the air medium. What will happen if a dielectric slab is inserted between them?
a) The slab will get heated
b) Current will flow through the slab
c) Two charges will attract each other
d) The net force between the charges will be reduced

Answer: d
Clarification: Force between two charges is inversely proportional to the relative permittivity of the medium between them. A dielectric slab has relative permittivity more than that of air. So the force between the charges decreases. No current or heating will be noticed.

10. According to Coulomb’s Law force between two charges is k*q1*(frac {q_2}{r^2}). What will happen if one of the charges is zero?
a) No attraction or repulsion
b) Always attraction
c) Always repulsion
d) Cannot predict the nature of the force

Answer: b
Clarification: Though it seems from the formula that the force must be zero, an opposite charge is induced on the uncharged body and then the two opposite charges will attract each other. This also proves that induction occurs before attraction.

11. What will be permittivity of a medium which has dielectric constant 5.4?
a) 4.78*10-11 C2N-1m-2
b) 8.85*10-10C2N-1m-2
c) 4.5*10-10C2N-1m-2
d) 3.2*10-11C2N-1m-2

Answer: a
Clarification: εo=8.854*10-12C2N-1m-2. Therefore the permittivity will be 5.4*8.854*10-12C2N-1m-2 = 4.78*10-11C2N-1m-2. We know that permittivity of a medium is equal to its relative permittivity multiplied to the absolute permittivity of air. Air has relative permittivity =1.

12. The dimension of εo _______
a) [M-1L-3T4I2]
b) [M-1L-3T4I4]
c) [M-1L-3T2I2]
d) [M1L-3T4I2]

Answer: a
Clarification: εo is the absolute permittivity of air medium and has value 8.854*10-12C2N-1m-2. Its dimension is [M-1L-3T4I2]. The permittivity of a medium is the product of this term with the dielectric constant or relative permittivity of that medium.

13. What is the C.G.S. unit of charge?
a) Stat Coulomb
b) Coulomb
c) EMU
d) Pascal

Answer: a
Clarification: The C.G.S. unit of charge is Stat Coulomb or ESU but in the SI system the unit is Coulomb. EMU is another unit of charge in the SI system. Pascal is the unit of pressure.

250+ TOP MCQs on Dielectrics and Polarisation | Class12 Physics

Physics Multiple Choice Questions on “Dielectrics and Polarisation”.

1. In which type of molecule positive and negative charges coincide with each other?
a) Polar
b) Unipolar
c) Non-polar
d) Bipolar
Answer: c
Clarification: A molecule in which the centre of mass of positive and negative charges collide with each other is called a non-polar molecule. They normally have zero dipole moment. They have symmetrical shapes.

2. What is the ratio of the polarization to εo times the electric field called?
a) Polarisation density
b) Electric susceptibility
c) Dielectric strength
d) Dielectric susceptibility
Answer: b
Clarification: The ratio of the polarization to εo times the electric field is called the electric susceptibility of the dielectric. It describes the electrical behaviour of a dielectric.

3. Which of the following is an example of a molecule whose centre of mass of positive and negative charges coincide each other?
a) CO2
b) CO
c) CH3OH
d) NH3
Answer: a
Clarification: CO2 is a molecule in which the centre of mass of positive and negative charges collide with each other and is called a non-polar molecule. They normally have zero dipole moment. They have symmetrical shapes.

4. What is the induced dipole moment developed per unit volume of a dielectric when placed in an external electric field called?
a) Relative permittivity
b) Polarisation susceptibility
c) Electric susceptibility
d) Polarisation density
Answer: d
Clarification: The induced dipole moment developed per unit volume of a dielectric when placed in an external electric field is called polarization density. It may be defined as the charge induced per unit surface area.

5. In which type of molecule positive and negative charges does not coincide with each other?
a) Isentropic
b) Equipotential
c) Polar
d) Non-polar
Answer: c
Clarification: A molecule in which the centre of mass of positive and negative charges does not collide with each other is called a polar molecule. They have a permanent dipole moment. They have unsymmetrical shapes.

6. The molecules of a polar dielectric have no dipole moment. State true or false.
a) True
b) False
Answer: b
Clarification: The molecules of a polar dielectric have permanent dipole moments. In the absence of an external electric field, the dipole moments of different molecules are randomly oriented due to thermal agitation in the material.

7. ‘X’ is a substance which does not allow the flow of charges through it but permits them to exert electrostatic forces on one another through it. Identify X.
a) Polar molecule
b) Dielectric
c) Non-polar molecule
d) Equipotential
Answer: b
Clarification: A dielectric is a substance which does not allow the flow of charges through it but permits them to exert electrostatic forces on one another through it. A dielectric is essentially an insulator which can be polarized through small localized displacements of its charges.

8. Which of the following is an example of a molecule whose centre of mass of positive and negative charges does not coincide each other?
a) NH3
b) H2
c) CH4
d) CO2
Answer: a
Clarification: NH3 is a molecule in which the centre of mass of positive and negative charges does not collide with each other and is called a polar molecule. They have a permanent dipole moment. They have unsymmetrical shapes.

250+ TOP MCQs on Current Electricity – Cells, Emf and Internal Resistance | Class12 Physics

Physics Exam Questions for Schools on “Current Electricity – Cells, Emf and Internal Resistance”.

1. Which of the following is the correct statement regarding electrochemical cell?
a) It converts chemical energy to electrical energy
b) It converts electric energy to chemical energy
c) It converts chemical energy to thermal energy
d) It does not maintain the flow of charge in a circuit
Answer: a
Clarification: An electrochemical cell is a device which converts chemical energy to electric energy, and maintains the flow of charge in a circuit. There are 2 types of electrochemical cells – Galvanic cell and Electrolytic cell.

2. Pick out the dimensional formula of emf from the following.
a) [M1L2T3A1]
b) [ML3T3A1]
c) [M2L2T1A-1]
d) [ML2T-3A-1]
Answer: d
Clarification: Electromotive force (emf) is defined as the potential difference between the two terminals of a cell in an open circuit. The SI unit of emf is (frac {joule}{coulomb}) or volt. So, its dimensional formula is [ML2T-3A-1].

3. Which is the factor that internal resistance does not depend on?
a) Distance between the electrodes
b) Temperature of the electrolyte
c) Nature of electrode and electrolyte
d) Area of the electrode, immersed in the electrolyte
Answer: b
Clarification: Internal resistance is defined as the resistance offered by the electrolyte and electrodes of a cell when the current flows through it. Internal resistance depends on distance between the electrodes, the nature of electrodes and electrolyte, and area of the electrode immersed in the electrolyte. So, that leaves temperature of the electrolyte out, which is the answer.

4. The emf of a cell depends upon concentration of the electrolyte.
a) True
b) False
Answer: a
Clarification: The emf of a cell depends upon the nature of electrodes, nature and concentration of electrolyte used in the cell and its temperature as well. Emf of a cell is inversely proportional to the concentration of the electrolyte.

5. Identify the correct statement from the following about discharging of a cell.
a) The direction of current in the cell is from positive to negative terminal
b) Terminal potential difference is greater than emf of the cell
c) Terminal potential difference is lesser than emf of the cell
d) The current increases and decreases frequently
Answer: c
Clarification: During discharging of a cell terminal potential difference, the terminal potential difference is lesser than the emf of the cell. The direction of current inside the cell is from negative terminal to positive terminal.

6. A current of 3 A passes through an electric circuit for 5 minutes and does a work of 900J. What is the emf of the source?
a) 3V
b) 1V
c) 5V
d) 10V
Answer: b
Clarification: Current = 3 A; Time taken = 5 minutes = 300 seconds
Work done = 900 J; Power = (frac {Work , done}{Time , taken} = frac {900}{300}) = 3 W
Power = Voltage (emf) x Current → Emf = (frac {Power}{Current} = frac {3}{3}) = 1V
Therefore, the emf of the source is 1 volt.

7. The emf of a battery is 86V and internal resistance 1 ohms in the figure shown below. Calculate the current drawn from the battery.

a) 2 A
b) 3 A
c) 5 A
d) 6 A
Answer: d
Clarification: The resistances 8 ohms, 10 ohms, and 2 ohms are in series, so the equivalent resistance is: RS = 8 + 10 + 2 = 20 ohms; RS and 4 ohms are in parallel connection to each other, so,
(frac {1}{R_P} = frac {1}{20} + frac {1}{4} = frac {3}{10}) → RP = (frac {10}{3})
Total resistance (R) = 3 + (frac {10}{3}) + 7 + 1 (internal resistance) = (frac {43}{3})
According to Ohm’s Law → V = IR → I = (frac {V}{R} = frac {86}{frac {34}{3}})
= 3 × 2
= 6 A
Therefore, the current drawn from the battery is 6 amperes.

8. A cell has an emf of 6V, internal resistance of 1 ohms and a current of 0.5 A passing through it. This cell is connected to a resistor. Find out the resistance of the resistor.
a) 10 ohms
b) 11 ohms
c) 12 ohms
d) 13 ohms
Answer: b
Clarification: Emf (e) = 6V; Internal resistance (r) = 1 ohms; Current (I) = 0.5A
Required equation: I = (frac {e}{R}) + r
0.5 = (frac {6}{R}) + 1
R = (frac {(6 – 0.5)}{0.5})
R = 11 ohms
Therefore, the resistance of the resistor is 11 ohms.

9. A group of N cells such its emf EN = 1.5rN is shown in the diagram below. What is the current I in the circuit?

a) 51 A
b) 0.015 A
c) 1.5 A
d) 155.1 A
Answer: c
Clarification: The total emf can be calculated as: E = E1 + E2 + E3 + …………… + EN
(According to the relation given) = 1.5r1 + 1.5r2 + 1.5r3 + ………… + 1.5rN
= 1.5 (r1 + r2 + r3 + ………… + rN) → X
Total resistance can be calculated as: R = r1 + r2 + r3 + ……….. + rN → Y
Substituting Y in X
E = 1.5 × R
We also know that → I = (frac {E}{R})
So, I = (frac {E}{R}) = 1.5 A
Therefore, the current in the circuit = 1.5 ampere

10. Which of the following devices is the more accurate one for the measurement of emf?
a) Meter Bridge
b) Voltmeter
c) Multimeter
d) Potentiometer
Answer: d
Clarification: Potentiometer is the more accurate device to measure emf than the other ones such as multimeter or voltmeter. Potentiometer is highly sensitive and thus, even small emfs can be measured using this device. Moreover, potentiometers do not draw current from the circuit during measurements, like voltmeters.

Physics Exam Questions for Schools,

250+ TOP MCQs on Bar Magnet | Class12 Physics

Physics Multiple Choice Questions on “Bar Magnet”.

1. Which among the following is not attracted by magnets?
a) Iron
b) Cobalt
c) Copper
d) Nickel
Answer: c
Clarification: A magnet is a material that has both attractive and directive properties. It attracts small pieces of iron, nickel, cobalt, etc. This property of attraction is called magnetism. Going by this criteria, copper is not attracted by magnets.

2. Identify the direction in which a thin long piece of magnet comes to rest when suspended freely.
a) East-west
b) North-south
c) Northeast-southeast
d) Northwest-southwest
Answer: b
Clarification: When suspended freely, a thin long piece of magnet comes to rest nearly in the geographical north-south direction. When placed in a non-uniform magnetic field, it tends to move from weaker to stronger magnetic field.

3. Which of the following is not a basic property of magnets.
a) Magnet exists as a monopole
b) Attractive property
c) Directive property
d) Like poles repel and unlike poles attract
Answer: a
Clarification: Attractive property, directive property and the law of magnetic poles are some of the important properties of magnets. So unlike electric charges, magnetic monopoles do not exist. Every magnet exists as a dipole.

4. Give the SI unit of magnetic dipole moment.
a) A-2m
b) Am-2
c) A2m
d) Am2
Answer: d
Clarification: The magnetic dipole moment of a magnetic dipole is defined as the product of its pole strength and magnetic length. The SI unit of magnetic dipole moment is ampere metre2 (Am2). Magnetic dipole moment is a vector quantity and is directed from south to north pole of the magnet.

5. Which of the following is a natural magnet?
a) Magnetic needle
b) Bar magnet
c) Magnetite
d) Horseshoe magnet
Answer: c
Clarification: Pieces of naturally occurring iron ore, lodestone or magnetite had the property of attracting small pieces of iron. Hence, magnetite is a natural magnet. All natural magnets are permanent magnets, meaning they will never lose their magnetic power.

6. Magnetic lines of force always form open loops. State true or false.
a) True
b) False
Answer: b
Clarification: Magnetic poles always exist in pairs. So magnetic lines of force run from N-pole to S-pole outside the magnet and from S-pole to N-pole inside the magnet. They do not start or end anywhere and always forms closed loops.

7. A magnet can only repel another magnet. So, ‘X’ is a surer test of magnetism. Identify X.
a) Directive
b) Repulsion
c) Remanence
d) Hysteresis
Answer: b
Clarification: A magnet can attract another magnet or a magnetic substance like iron. However, a magnet can repel another magnet only. So repulsion is the surer test of magnetism.

8. A magnetic dipole of length 10 cm has pole strength of 20 Am. Find the magnetic moment of the dipole.
a) 2 Am2
b) 200 Am2
c) 20 Am2
d) 0.2 Am2
Answer: a
Clarification: Magnetic dipole moment = Pole strength × Magnetic length.
Magnetic dipole moment = 20 Am × 0.1 m
Magnetic dipole moment = 2 Am2.

9. A magnetized needle of the magnetic moment 20 JT-1 is placed at 60o with the direction of the uniform magnetic field of magnitude 9 T. What is the torque acting on the needle?
a) 225 J
b) 625 J
c) 155.8 J
d) 318 J
Answer: c
Clarification: Torque, τ = mBsin (θ).
Given: m = 20 J/T; B =9 T; θ = 60o
τ = 20 JT-1 × 9 T × sin(60o)
τ = 155.8J.

10. A bar magnet of the magnetic moment 5 Am2 has poles 20 cm apart. Calculate the pole strength.
a) 250 Am
b) 4 Am
c) 100 Am
d) 25 Am
Answer: d
Clarification: Magnetic dipole moment = Pole strength × Magnetic length.
Pole strength = (frac {Magnetic , dipole , moment}{Magnetic , length})
Pole strength = (frac {5}{0.2})
Pole strength = 25 Am.