250+ TOP MCQs on Einstein’s Photoelectric Equation : Energy Quantum of Radiation | Class12 Physics

Physics Multiple Choice Questions on “Einstein’s Photoelectric Equation : Energy Quantum of Radiation”.

1. Two beams, one of red light and the other of blue light, of the same intensity are incident on a metallic surface to emit photoelectrons. Which emits electrons of greater frequency?
a) Both
b) Red light
c) Blue light
d) Neither
Answer: c
Clarification: From Einstein’s photoelectric equation, we have
(frac {1}{2}) mv2 = h(v – v0).
Since the frequency of blue light is greater than that of the red light, blue light emits electrons of greater kinetic energy.

2. If the intensity of incident radiation in a photo-cell is increased, how does the stopping potential vary?
a) Increases
b) Remains the same
c) Decreases
d) Infinite
Answer: b
Clarification: There is no effect on stopping potential. The intensity of incident radiation is independent of stopping potential. Therefore, even if the incident radiation in a photo-cell is increased, the stopping potential remains unchanged.

3. If the frequency of the incident radiation is equal to the threshold frequency, what will be the value of the stopping potential?
a) 0
b) Infinite
c) 180 V
d) 1220 V
Answer: a
Clarification: From Einstein’s photoelectric equation, we have
(frac {1}{2}) mv2 = h(v – v0).
When v = v0,
hv0 = hv0 + eV0
Therefore, V0 = 0.

4. How does retarding potential vary with the frequency of light causing photoelectric effect?
a) Infinite
b) Zero
c) Decreases
d) Increases
Answer: d
Clarification: The stopping potential is directly proportional to the frequency of light.
Hence, the stopping potential increases with an increase in the frequency of the incident light.

5. If the intensity of the radiation incident on a photo-sensitive plate is doubled, how does the stopping potential change?
a) Increases
b) Decreases
c) No effect
d) Infinite
Answer: c
Clarification: No effect. This is because the intensity of radiation incident on a photo-sensitive plate is independent on stopping potential. So, the stopping potential remains the same, even if the intensity is doubled.

6. The stopping potential in photoelectric emission does not depend upon the frequency of the incident radiation.
a) True
b) False
Answer: b
Clarification: The stopping potential depends on the frequency of incident radiation. Above the threshold frequency, the stopping potential is directly proportional to the frequency of incident radiation.

7. The maximum kinetic energy of a photoelectron is 3 eV. What is the stopping potential?
a) 0 V
b) 3 V
c) 9 V
d) 12 V
Answer: b
Clarification: Stopping potential is given as:
V0 = (frac {K_{max}}{e})
V0 = (frac {3eV}{e})
V0 = 3 V
Therefore, the stopping potential is 3 V.

8. The stopping potential in an experiment on the photoelectric effect is 1.5 V. What is the maximum kinetic energy of the photoelectrons emitted?
a) 1.5 eV
b) 3 eV
c) 4.5 eV
d) 6 eV
Answer: a
Clarification: Kmax = eV0
Kmax = 1.6 × 10-19 C × 1.5 V
Kmax = 24 × 10-19 J
It can also be converted into units of electron volts that will be:
Kmax = 1.5 eV

9. For a photosensitive surface, the work function is 3.3 × 10-19 J. Calculate the threshold frequency.
a) 15 × 1014 Hz
b) 25 × 1014 Hz
c) 5 × 1014 Hz
d) 55 × 1014 Hz
Answer: c
Clarification: Threshold frequency is given as:
v0 = (frac {W_0}{h})
v0 = (frac {W_0}{h})
v0 = (frac {(3.3 times 10^{-19})}{(6.6 times 10^{-34})})
v0 = 5 × 1014 Hz.

10. Calculate the kinetic energy of a photoelectron (in eV) emitted on shining light of wavelength 6.2 × 10-6 m on a metal surface. The work function of the metal is 0.1 eV.
a) 10 eV
b) 0.1 eV
c) 0.01 eV
d) 1000 eV
Answer: b
Clarification: Kmax = (( frac {hc}{lambda })) – W0
Kmax = ( [ frac {(6.6 times 10^{-34} times 3 times 10^8 )}{(6.2 times 10^{-6} times 1.6 times 10^{-19}) }] ) – 0.1.
Kmax = 0.2 – 0.1
Kmax = 0.1 eV

250+ TOP MCQs on Semiconductor Diode | Class12 Physics

Physics Multiple Choice Questions on “Semiconductor Diode”.

1. Why is there a sudden increase in current in Zener diode?
a) Due to the rupture of ionic bonds
b) Due to rupture of covalent bonds
c) Due to viscosity
d) Due to potential difference
Answer: b
Clarification: The sudden increase in current in a Zener diode is due to the rupture of the many covalent bonds present. Therefore, the Zener diode should be connected in reverse bias.

2. What is the semiconductor diode used as?
a) Oscillator
b) Amplifier
c) Rectifier
d) Modulator
Answer: c
Clarification: Semiconductor diode can be used as a rectifier. The function of a rectifier is that it converts an alternating current into direct current by allowing the current to pass through in one direction.

3. What is an oscillator?
a) An amplifier with a large gain
b) An amplifier with negative feedback
c) An amplifier with positive feedback
d) An amplifier with no feedback
Answer: c
Clarification: An oscillator is considered as an amplifier with positive feedback. It converts direct current from a power supply to an alternating current signal. It produces an alternating waveform without any input.

4. What is rectification?
a) Process of conversion of ac into dc
b) Process of conversion of low ac into high ac
c) Process of conversion of dc into ac
d) Process of conversion of low dc into high dc
Answer: a
Clarification: Rectification is the process of conversion of alternating current into direct current. The conversion first powers to alternating current then use a transformer to change the voltage, and finally rectifies power back to direct current.

5. What is a Zener diode used as?
a) Oscillator
b) Regulator
c) Rectifier
d) Filter
Answer: b
Clarification: Zener diode can be used as a voltage regulator. They can also be used as shunt regulators to regulate the voltage across small circuits. Zener diodes are always operated in a reverse-biased condition.

6. Forward biasing of p-n junction offers infinite resistance.
a) True
b) False
Answer: b
Clarification: No, this is a false statement. Forward biasing of p-n junction offers low resistance. In the case of an ideal p-n junction, the resistance offered is zero. So, forward biasing does not offer any resistance.

7. When a junction diode is reverse biased, what causes current across the junction?
a) Diffusion of charges
b) Nature of material
c) Drift of charges
d) Both drift and diffusion of charges
Answer: c
Clarification: The reverse current is mainly due to the drift of charges. It is due to the carriers like holes and free electrons passing through a square centimeter area that is perpendicular to the direction of flow.

8. Identify the condition for a transistor to act as an amplifier.
a) The emitter-base junction is forward biased and the base-collector junction is reverse biased
b) No bias voltage is required
c) Both junctions are forward biased
d) Both junctions are reverse biased
Answer: a
Clarification: In order to use a transistor as an amplifier the emitter-base junction is set up as forward biased and the base-collector junction is set up as reverse biased. This is the criteria for making a transistor function as an amplifier.

9. What can a p-n junction diode be used as?
a) Condenser
b) Regulator
c) Amplifier
d) Rectifier
Answer: d
Clarification: A junction diode can be used as a rectifier. The rectifier converts alternating current into direct current. During the positive half cycle, the diode is forward biased and allows electric current through it.

10. What is a transistor made up of?
a) Chip
b) Insulator
c) Semiconductor
d) Metal
Answer: c
Clarification: A transistor is a semiconductor device. Transistors can work either as an amplifier or as a switch. It is used to amplify or switch electronic signals. A transistor is a solid-state device made up of silicon and germanium.

250+ TOP MCQs on Electrostatic Potential | Class12 Physics

Physics Multiple Choice Questions on “Electrostatic Potential”.

1. Work done to bring a unit positive charge from infinity to a point in an electric field is known as _______
a) Electric potential
b) Electric field intensity
c) Electric dipole moment
d) The total energy of the point charge

Answer: a
Clarification: Electric potential is defined as the amount of work done to bring a unit positive charge from an infinite distance to a particular point of an electric field. The total energy of that point charge means the sum of kinetic energy and potential energy which is not the same as the potential energy if the particle is in motion.

2. If a charged body is moved in an electric field against the Coulomb force, then ________
a) Work is done on the body by an external agent
b) Work is done by the electric field
c) Electric field intensity decreases
d) The total energy of the system decreases

Answer: a
Clarification: To move a body against some force, work is to be done on the body. In this case, an external force is to be applied on the body to move it i.e. an external work is to be done. As we are moving the body against the Coulomb’s force, hence no work is done on the body by the electric field.

3. What is the dimension of electric potential?
a) [M L T-2]
b) [M L T-3 I]
c) [M L T-3 I-1]
d) [M L2 T-3 I]

Answer: c
Clarification: Potential can be simply defined as work done on a unit charge, therefore the dimension=(frac {the , dimension , of , work}{the , dimension , of , charge}=frac {[M L T^{-2}]}{[I T]})=[M L T-3 I-1]. The dimension of potential energy in mechanics is not the same as electric potential energy though both of them are the unit of energy. In mechanics, it is defined as work done on a unit mass.

4. Electric potential varies with distance such that V(x) =ax-bx3; where a and b are constants. Where will the electric field intensity be zero?
a) x=(frac {a}{b})
b) x=(frac {a}{3b})
c) x=(sqrt{frac {a}{b}})
d) x=+(sqrt{frac {a}{3b}}) and x=-(sqrt{frac {a}{3b}})

Answer: d
Clarification: We know that E=-(frac {dv}{dx})
∴ E = –(frac {d}{dx}) (ax – bx3) = -(a – 3bx2)
Electric field will be zero. ∴ E = 0 ⇒ (a-3bx2) = 0
⇒ a = 3bx2
⇒ x2 = (frac {a}{3b}) = x = ±(sqrt{frac {a}{3b}})

5. 1 electron volt= __________ J.
a) 1.6*10-19
b) 4.8*10-19
c) 1.6*10-10
d) 10

Answer: a
Clarification: 1 electron volt is the amount of work done if an electron is passed through a potential difference of 1V. Therefore the work done = 1V*charge of an electron = 1.602*10-19 J. But it is a small quantity and hence we use kilo electron volt and mega electron volt in practical.

6. 1 V/m= _______
a) 1N/C
b) 3*1010 N/C
c) 107 N/C
d) 1010 N/C

Answer: a
Clarification: From the definition, we know that electric field E=(frac {-dv}{dx}). Therefore V/m is the unit of electric field intensity. 1 V/m means the amount of electric field in which if we move a unit positive charge by 1 m, the work done will be 1N. Therefore, the electric field will be 1N/C.

7. The electric potential difference between two points is a path function. The statement is __________
a) True
b) False

Answer: b
Clarification: Electric potential depends only on the electric field intensity and the amount of charge. It has no dependency on the path by which the charge is traveling. Therefore, if we move a charge from one point to another in presence of an electric field in a straight line or a curve line, work done in both the cases will be the same i.e. potential difference between the points will be the same.

8. By performing a set of experiments, a scientist found that the electric field between two points A and B is zero. What can he conclude regarding the potential of the two points?
a) VA=0, VB=0
b) VA>VB
c) VA+VB
d) VA=VB

Answer: d
Clarification: We know thatVAB=VA-VB=-(int_A^B)E.dx. But E=0, so the value of the integral becomes zero. Therefore VA=VB is obtained. The electric field is always directed from a point of higher potential to a point of lower potential. But if the potential of two points is the same, i.e. no potential difference, then there will be no electric field.

9. Earth’s potential is _______
a) Zero
b) Highly positive
c) Highly negative
d) Varies from place to place

Answer: a
Clarification: We consider earth as the storage of infinite positive as well as a negative charge. Therefore, the potential of the earth is always considered to be zero and the potential of every body is measured with respect to earth. That’s why if we connect any charged body to the earth, its potential instantaneously becomes zero.

300+ TOP Ohm’s Law MCQs and Answers | Class12 Physics

Ohm’s Law Multiple Choice Questions

1. Ohm’s law is true for

A. Metallic conductors at low temperature
B. Metallic conductors at high temperature
C. For electrolytes, when current passes through them
D. For diode when current flows

Answer: A. Metallic conductors at low temperature

2. An example of non-ohmic resistance is

A. Diode
B. Tungsten wire
C. Carbon resistance
D. Copper wire

Answer: A. Diode

3. If a current of 5 Amperes flows through the conductor. The number of electrons per second will is

A. 1.6 x 10-19
B. 3.12 x 1019
C. 4 x 1019
D. 7.68 x 1020

Answer: B. 3.12 x 1019

4. In a conductor, if 6-coulomb charge flows for 2 seconds. The value of electric current will be

A. 3 ampere
B. 3 volts
C. 2 amperes
D. 2 volts

Answer: A. 3 amperes

5. An EMF source of 8.0 V is connected to a purely resistive electrical appliance. An electric current of 2.0 A flows through it. What is the resistance offered by the electrical appliances?

A. 4 ohm
B. 6 ohm
C. 2 ohm
D. 3 ohm

Answer: A. 4 ohm

6. A potential difference of 10 V is applied across a conductor whose resistance is 2.5 ohm. What is the value of current flowing through it?

A. 4 amperes
B. 2 amperes
C. 6 amperes
D. 10 amperes

Answer: A. 4 amperes

7. If the conductor resistance is 50 ohm and the current passing through it is 5 A. What is the value of potential difference?

A. 150 V
B. 250 V
C. 50 V
D. 15 V

Answer: B. 250 V

8. When the length of the conductor is doubled and the area of cross-section remains the same then its resistance

A. Remains the same
B. Will be doubled
C. Will become half
D. Will increase by four times

Answer: B. Will be doubled

9. The current passing through a resistor in a circuit is 1 A when the voltage across the same resistor is 10 V. What is the value of current when the voltage across the resistor is 8 V

A. 0.8 A
B. 8 A
C. 80 A
D. 18 A

Answer: A. 0.8 A

10. Two resistors R1 and R2 with resistance 5 ohms and 10 ohms respectively are connected in series. The voltage across R1 is 4 V. What will be the value of current across R2.

A. 0.8 A
B. 8 A
C. 80 A
D. 18 A

Answer: A. 0.8 A

Ohm’s Law objective questions with answers pdf download online exam test

250+ TOP MCQs on Magnetic Field due to a Current Element & Biot-Savart Law | Class12 Physics

Physics Problems for Schools on “Magnetic Field due to a Current Element & Biot-Savart Law”.

1. Give the SI unit of magnetic permeability of free space.
a) T A m-2
b) T A-2 m
c) T A-1 m
d) T A m2
Answer: c
Clarification: Magnetic permeability of free space is a measure of the amount of resistance encountered when forming a magnetic field in a classical vacuum. The SI unit of permeability is weber ampere-1 metre-1 (Wb A-1 m-1) or tesla ampere-1meter (T A-1 m).

2. State the rule that is used to find the direction of field acting at a point near a current-carrying straight conductor.
a) Cork rule
b) The right-hand thumb rule
c) Swimming rule
d) Flemings rule
Answer: b
Clarification: Right-hand thumb rule can be used to find the direction of the magnetic field at a point near a current-carrying conductor. Right hand rule states that, if the thumb of the right hand is in the direction of the current flow then, the curl fingers show the direction of the magnetic field.

3. Give the dimensional formula for magnetic permeability of free space.
a) [M L T-2 A-2]
b) [M2 L T-2 A-2]
c) [M L2 T-2 A-2]
d) [M-1 L T-2 A-2]
Answer: a
Clarification: Magnetic permeability = Magnetic flux density × [Magnetic field strength]-1.
μ = [M L0 T-2 A-1] × [M0 L-1 T0 A1]-1
μ = [M L T-2 A-2].

4. A wire placed along the north-south direction carries a current of 8 A from south to north. Find the magnetic field due to a 1 cm piece of wire at a point 200 cm north-east from the piece.
a) 14 × 10-9 T
b) 1004 × 10-9 T
c) 204.4 × 10-9 T
d) 1.4 × 10-9 T
Answer: d
Clarification: dB = (frac {(mu_0 I dl sin (theta))}{(4pi r^2)}).
dB = (frac {(4 pi , times , 10^{-7} , times , 8 , times , 1 , times , 10^{-2} , times , sin 45^o}{(4 pi , times , 22)})
dB = 1.4 × 10-9 T.

5. Which of the following is not a point of similarity between Biot-Savart law and Coulomb’s law.
a) Both fields depend inversely on the square of the distance from the source to the point of observation
b) They are not a universal law
c) The principle of superposition does not apply to both
d) Both are long-range fields
Answer: c
Clarification: The principle of superposition applies to both fields. This is because the magnetic field is linearly related to its source, namely, the current element and the electrostatic field is related linearly to its source, the electric charge.

6. The magnetic field due to a current element is minimum in a plane passing through the element when it is perpendicular to its axis. State true or false.
a) True
b) False
Answer: b
Clarification: If θ = 90o → sin θ = 1
→ Then dB is maximum.
The magnetic field due to a current element is maximum in a plane passing through the element and perpendicular to its axis.

7. Give the SI unit of the magnetic field from Biot-Savart law.
a) Ampere
b) Tesla
c) Weber
d) Gauss
Answer: b
Clarification: The SI unit of the magnetic field is the tesla (T). One tesla is 107 times the magnetic field produced by a conducting wire of length one meter and carrying a current of one ampere at a distance of one meter from it and perpendicular to it.

Physics Problems for Schools,

250+ TOP MCQs on Electromagnetic Induction – Lenz’s Law and Conservation of Energy | Class12 Physics

Physics Multiple Choice Questions on “Electromagnetic Induction – Lenz’s Law and Conservation of Energy”.

1. A closed-loop move normal to the constant electric field between the plates of a large capacitor. What is the amount of current produced when it is wholly inside the region between the capacitor plates?
a) Maximum
b) Minimum
c) Zero
d) Independent of current
Answer: c
Clarification: No current is produced when it is wholly inside the region between the capacitor plates. Current cannot be induced by changing electric flux. So, the amount of current produced when it is wholly inside the region between the capacitor plates is zero.

2. Which law is used in finding the direction of current in an a.c. generator?
a) Maxwell’s law
b) Lenz’s law
c) Corkscrew law
d) Ampere circuital law
Answer: b
Clarification: In an a.c. generator, induced current due to a change of magnetic flux linked with a closed circuit can be found out using Lenz’s law. Lenz’s law, in electromagnetism, statement that an induced electric current flows in a direction such that the current opposes the change that induced it.

3. Which of the following statement is valid?
a) Lenz’s law is a consequence of the law of conservation of energy
b) Lenz’s law is a consequence of the law of conservation of momentum
c) Lenz’s law is a consequence of the law of conservation of force
d) Lenz’s law is a consequence of the law of conservation of mass
Answer: a
Clarification: Whether a magnet is moved towards or away from a closed coil, the induced current always opposes the motion of the magnet, as predicted by Lenz’s law. Work has to be done in moving the magnet closer to the coil against this force of repulsion. Thus Lenz’s law is valid and is a consequence of the law of conservation of energy.

4. The current in a wire passing normally through the center of a conducting loop is increasing at a constant rate. What is the net current induced in the loop?
a) Indefinite
b) Maximum
c) Minimum
d) Zero
Answer: d
Clarification: The magnetic lines of force due to current are parallel to the plane of the loop. The flux linked with the loop is zero. Hence no current is induced in the loop.

5. Which of the following is found using Lenz’s law?
a) Induced emf
b) Induced current
c) The direction of induced emf
d) The direction of alternating current
Answer: c
Clarification: Lenz’s law is a general law for determining the direction of induced emf and hence that of induced current in a circuit. Lenz’s law states that the direction of an induced emf will be such that if it were to cause a current to flow in a conductor in an external circuit, then that current would generate a field that would oppose the change that created it.

6. Lenz’s law is invalid. State true or false.
a) True
b) False
Answer: b
Clarification: When a magnet is moved towards or away from a closed coil, the induced current always opposes the motion of the magnet, as predicted by Lenz’s law. Thus Lenz’s law is valid and is a consequence of the law of conservation of energy.

7. ‘X’ states that the direction of induced current in a circuit is such that it opposes the cause or the change which produces it. Identify X.
a) Faraday’s law
b) Lenz’s law
c) Maxwell’s law
d) Ampere’s law
Answer: b
Clarification: Lenz’s law states that the direction of induced current in a circuit is such that it opposes the cause or the change which produces it. It is a general law for determining the direction of induced emf and hence that of induced current in a circuit.

8. Identify the law used to find the direction of eddy currents.
a) Lenz’s law
b) Maxwell’s law
c) Ampere’s law
d) Faraday’s law
Answer: a
Clarification: Eddy currents are the currents induced in solid metallic masses when the magnetic flux threading through them changes. Eddy currents also oppose the change in magnetic flux, so their direction is given Lenz’s law.

Physics Multiple Choice Questions and Answers for Class 12,