CBSE Class 12 Physics Question Paper 2021 (Term-I) with Solutions

Students can use CBSE Previous Year Question Papers Class 12 Physics with Solutions and CBSE Class 12 Physics Question Paper 2021 (Term-I) to familiarize themselves with the exam format and marking scheme.

CBSE Class 12 Physics Question Paper 2021 (Term-I) with Solutions

Time Allowed: 90 minutes
Maximum Marks: 35

General Instructions:

1. This Question paper contains 55 questions out of which 45 questions are to be attempted. All questions carry equal marks.
2. This Question paper consists of three Sections – Section A, B and C.
3. Section—A contains 25 questions. Attempt any 20 questions from Q. No. 1 to 25.
4. Section — B contains 24 questions. Attempt any 20 questions from Q. No. 26 to 49.
5. Section—C contains 6 questions. Attempt any 5 questions from Q. No. 50 to 55.
6. The first 20 questions attempted in Section A & Section B and first 5 questions attempted in Section C by a candidate will be evaluated.
7. There is only one correct option for every Multiple Choice Question (MCQ). Marks will not be awarded for answering more than one option.
8. There is no negative marking.

Section – A

This section consists of 25 Multiple Choice Questions with overall choice to attempt any 20 questions. In case more than desirable number of questions are attempted, only first 20 questions will be considered for evaluation.

Question 1.
A negatively charged object X is repelled by another charged object Y. However an object Z is attracted to object Y. Which of the following is the most possibility for the object Z?
(a) positively charged only
(b) negatively charged only
(c) neutral or positively charged
(d) neutral or negatively charged
Answer:
(c) neutral or positively charged

Neutral or positively charged

Question 2.
In an experiment three microscopic latex spheres are sprayed into a chamber and became charged with charges +3e, +5e and -3c respectively. All the three spheres came in contact simultaneously for a moment and got separated. Which one of the following are possible values for the final charge on the spheres? [1]
(a) +5e, -4e, +5e
(b) +6e, +6e, -7e
(c) +4e, +3.5e, +5.5c
(d) +5e, -8e, +7e
Answer:
(b) +6e, +6e, -7e

Net charge remains the same
Initial net charge = 3e + 5e – 3e = 5e
∴ Option (b) is having the same net charge : 6e + 6e – 7e = 5e

Question 3.
An object has charge of 1 C and gains 5.0 x 1018 electrons. The net charge on the object’ becomes: .
(a) -0.80 C
(b) +0.80 C
(c) +1.80C
(d) +0.20 C
Answer:
(d) +0.20 C

Given. Q = 1C
As we know, Q = ne
= -5 × 10 ¹⁸ × 1.6 × 10 ^-19
= -8 × 10 ^-1 = -0.8C ∴ Net charge = 1C – 0.8C = 0.20 C

Question 4.
Kirchhoff’s first rule ΣI = 0 and second rule ΣIR = ΣE (where the symbols have their usual meanings) are respectively based on —
(a) conservation of momentum and conservation of charge
(b) conservation of energy, conservation of charge
(c) conservation of charge, conservation of momentum
(d) conservation of charge, conservation of energy
Answer:
(d) conservation of charge, conservation of energy

Kirchoff’s 1 ^st law is based on law of-Conservation of charge and Kirchoff’s 2 ^nd law is based on law of Conservation of energy.

Question 5.
The electric power consumed by a 220 V -100 W bulb when operated at 110 V is
(a) 25 W
(b) 30 W
(c) 35 W
(d) 45 W
Answer:
(a) 25 W

Question 6.
Which of the following has negative temperature coefficient of resistivity?
(a) metal
(b) metal and semiconductor
(c) semiconductor
(d) metal and alloy
Answer:
(c) semiconductor

Semiconductor has a -ve temperature coefficient of resistivity whereas for metal and alloy, it will be positive.

Question 7.
Two wires carrying currents I ₁ and I ₂ lie, one slightly above the other, in a horizontal plane as shown in figure. The region of vertically upward strongest magnetic field is.

(a) I
(b) II
(c) III
(d) IV
Answer:
(b) II

∴ Region II is of vertically upward
Strongest magnetic field of work

Question 8.
Two parallel conductors carrying current of 4.0 A and 10.0 A are placed 2.5 cm apart in vacuum. The force per unit length between them is —
(a) 6.4 × 10 ^-5 N/m
(b) 6.4 × 10 ^-2 N/m
(c) 4.6 × 10 ^-4 N/m
(d) 3.2 × 10 ^-4 N/m
Answer:
(d) 3.2 × 10 ^-4 N/m

Given. I ₁ = 4A, I ₂ = 10A, d = 2.5 cm or 2.5 × 10 ^-2 m
F = \(\frac{\mu_0 I_1 I_2}{2 \pi d}\) = \(\frac{4 \pi \times 10^{-7} \times 4 \times 10}{2 \pi \times 2.5 \times 10^{-2}}\) = 3.2 × 10 ^-4 N/m

Question 9.
If an ammeter is to be used in place of a voltmeter, then we must connect with the ammeter a —
(a) low resistance in parallel
(b) low resistance in series
(c) high resistance in parallel
(d) high resistance in series
Answer:
(d) high resistance in series

High resistance in series. we know a voltmeter has a very high resistance as compared to ammeter. Hence, in order to use an ammeter in place of voltmeter we must connect a very high resistance in series with the ammeter.

Question 10.
The magnetic field at the centre of a current carrying circular loop of radius R, is B ₁ . The magnetic field at a point on its axis at a distance R from the centre of the loop is B ₂ . Then the ratio (B ₁ /B ₂ ) is
(a) 2\(\sqrt{2}\)
(b) \(\frac{1}{\sqrt{2}}\)
(c) \(\sqrt{2}\)
(d) 2
Answer:
(a) 2\(\sqrt{2}\)

Question 11.
The self-inductance of a solenoid of 600 turns is 108 mH. The self-inductance of a coil having 500 turns with the same length, the same radius and the same medium will be
(a) 95 mH
(b) 90 mH
(c) 85 mH
(d) 75 mH
Answer:
(d) 75 mH

Question 12.
The rms current in a circuit connected to a 50 Hz ac source is 15A. The value of the current in the circuit \(\left(\frac{1}{600}\right)\)s after the instant the current is zero, is-
(a) \(\frac{15}{\sqrt{2}}\)
(b) 15\(\sqrt{2}\)
(c) \(\frac{\sqrt{2}}{15}\)A
(d) 8A
Answer:
(a) \(\frac{15}{\sqrt{2}}\)

Question 13.
In a circuit the phase difference between the alternating current and the source voltage is \(\frac{\pi}{2}\). Which of the following cannot be the element(s) of the circuit?
(a) only C
(b) only L
(c) L and R
(d) L or C
Answer:
(c) L and R

Because in case of L and R, phase difference is less than 90° i.e., φ < 90°

Question 14.
The electric potential V at any point (x, y, z) is given by V = 3x ² where x is in metres and V in volts. The electric field at the point (1 m, 0, 2m) is –
(a) 6 V/m along -x-axis
(b) 6 V/m along +x-axis
(c) 1.5 V/m along -x-axis
(d) 1.5 V/m along+x-axis
Answer:
(a) 6 V/m along -x-axis

Given. V = 3x ²
As we know, E = \(\frac{-d \mathrm{~V}}{d x}\) = \(\frac{-d}{d x}\)(3x ² ) = -6x
∴ E = \(-6 x]_{x=1}\) = 1 ∴ E = -6 V/m
Hence, the electric field at the point (1, 0, 2) is 6 V/m along -x axis.

Question 15.
Which of the diagrams correctly represents the electric field between two charged plates if a neutral conductor is placed in between the plates?

Answer:
(d)

Electric field lines start form +ve charge and end at -ve charge.

Question 16.
A variable capacitor is connected to a 200 V battery. If its capacitance is changed from 2 µF to X µF, the decrease in energy of the capacitor is 2 × 10 ^-2 J. The value of X is —
(a) 1 µF
(b) 2 µF
(c) 3 µF
(d) 4 µF
Answer:
(a) 1 µF

Question 17.
A potential difference of 200 V is maintained across a conductor of resistance 100 Ω. The number of electrons passing through it in 1s is
(a) 1.25 × 10 ¹⁹
(b) 2.5 × 10 ¹⁸
(c) 1.25 × 10 ¹⁸
(d) 2.5 × 10 ¹⁶
Answer:
(a) 1.25 × 10 ¹⁹

Question 18.
The impedance of a series LCR circuit is —
(a) R + X _L + X _C
(b) \(\sqrt{\frac{1}{\mathrm{X}_{\mathrm{C}}^2}+\frac{1}{\mathrm{X}_{\mathrm{L}}^2}+\mathrm{R}^2}\)
(c) \(\sqrt{X_L^2-X_{\mathrm{C}}^2+\mathrm{R}^2}\)
(d) \(\sqrt{R^2+\left(X_L-X_C\right)^2}\)
Answer:
(d) \(\sqrt{R^2+\left(X_L-X_C\right)^2}\)

Impedance of series LCR circuit, Z = \(\sqrt{R^2+\left(\mathrm{X}_{\mathrm{L}}-\mathrm{X}_{\mathrm{C}}\right)^2}\)

Question 19.
When an alternating voltage E = E ₀ sin ωt is applied to a circuit, a current I = I ₀ sin \(\left(\omega t+\frac{\pi}{2}\right)\) flows through it. The average power dissipated in the circuit is.
(a) E _rms I _rms
(b) E ₀ I ₀
(c) \(\frac{E_0 I_0}{\sqrt{2}}\)
(d) Zero
Answer:
(d) Zero

As we know, P _avg = V _R I _R cos 90°
∴ P _avg = 0

Question 20.
A current carrying wire kept in a uniform magnetic field, will experience a maximum force when it is
(a) perpendicular to the magnetic field.
(b) parallel to the magnetic field.
(c) at an angle of 45° to the magnetic field.
(d) at an angle of 60° to the magnetic field.
Answer:
(a) perpendicular to the magnetic field.

\(\overrightarrow{\mathrm{F}}\) = I \(\vec{l} \times \overrightarrow{\mathrm{B}}\)
= I lB sin θ° = I /B sin 90°
= I lB
∴ l ⊥ B …. [maximum when θ = 90°

Question 21.
The voltage across a resistor, an inductor, and a capacitor connected in series to an ac source are 20 V, 15 V and 30 V respectively. The resultant voltage in the circuit is
(a) 5 V
(b) 20 V
(c) 25 V
(d) 65V
Answer:
(c) 25 V

Question 22.
In a DC circuit the direction of current inside the battery and outside the battery respectively are —
(a) Positive to Negative terminal and Negative to Positive terminal.
(b) Positive to Negative terminal and Positive to Negative terminal.
(c) Negative to Positive terminal and’Positive to Negative terminal.
(d) Negative to Positive terminal and Negative to Positive terminal.
Answer:
(c) Negative to Positive terminal and’Positive to Negative terminal.

Inside the battery electrons move from the to -ve plates of electrodes. So current flows from -ve terminal to +ve terminal, while outside the battery, the +ve charge moves from +ve terminal to +ve terminal.

Question 23.
The magnitude of electric field due to a point charge 2q, at distance r is E. Then the magnitude of electric field due to a uniformly charged thin spherical shell of radius R with total charge q at a distance \(\frac{r}{2}\) (r >> R) will be
(a) \(\frac{E}{4}\)
(b) 0
(c) 2E
(d) 4E
Answer:
(c) 2E

Electric field due to point charge, 2q

Question 24.
The net magnetic flux through any closed surface is :
(a) 1
(b) 0
(c) 90
(d) 180
Answer:
(b) 0

Question 25.
The current in the primary coil of a pair of coils changes from 7 A to 3 A in 0.04 s. The mutual inductance between the two coils is 0.5 H. The induced emf in the secondary coil is —
(a) 50 V
(b) 75 V
(c) 100 V
(d) 220 V
Answer:
(a) 50 V

Given, dt = 0.04s; dI = 3 – 7; L = 0.5 H
e = -L \(\frac{d \mathrm{I}}{d t}\) = -0.5 × \(\frac{(3-7)}{0.04}\) = \(\frac{-25 \times(-4)}{2}\)= 50 V

Section – B

Question 26.
A square sheet of side ‘a’ is lying parallel to XY plane at z = a. The electric field in the region is \(\overrightarrow{\mathrm{E}}\) = \(c z^2 \hat{\mathrm{k}}\). The electric flux through the sheet is
(a) a ⁴ c
(b) \(\frac{1}{3}\)a ³ c
(c) \(\frac{1}{3}\)a ⁴ c
(d) 0
Answer:
(a) a ⁴ c

Question 27.
Three charges q, -q and q ₀ are placed as shown in figure. The magnitude of the net force on the charge q ₀ at point O is [k = \(\frac{1}{\left(4 \pi \varepsilon_0\right)}\)].

(a) 0
(b) \(\frac{2 k q q_0}{a^2}\)
(c) \(\frac{\sqrt{2} k q q_0}{a^2}\)
(d) \(\frac{1}{\sqrt{2}} \frac{k q q_0}{a^2}\)
Answer:
(c) \(\frac{\sqrt{2} k q q_0}{a^2}\)

Question 28.
A + 3.0 nC charge Q is initially at rest at a distance of r ₁ = 10 cm from a + 5.0 nC charge q fixed at the origin. The charge Q is moved away from q to a new position at r ₂ = 15 cm. In this process work done by the field is
(a) 1.29 × 10 ^-5 J
(b) 3.6 × 10 ⁵ J
(c) -4.5 × 10 ^-7 J
(d) 4.5 × 10 ^-7 J
Answer:
(c) -4.5 × 10 ^-7 J

Question 29.
What is the work done in moving a test charge ‘q’ through a distance of 1 cm along equitorial axis of an electric dipole?
(a) 0
(b) ∞
(c) 1
(d) -1
Answer:
(a) 0

W = q∆V ….. [The Potential is zero at equatorial axis.

Question 30.
A straight conducting rod of length l and mass m is suspended in a horizontal plane by a pair of flexible strings in a magnetic field of magnitude B. To remove the tension in the supporting strings, the magnitude of the current in the wire is
(a) \(\frac{m g B}{l}\)
(b) \(\frac{m g l}{B}\)
(c) \(\frac{m g}{l \mathrm{~B}}\)
(d) \(\frac{I \mathrm{~B}}{m g}\)
Answer:
(c) \(\frac{m g}{l \mathrm{~B}}\)

Question 31.
A constant current is flowing through a solenoid. An iron rod is inserted in the solenoid along its axis. Which of the following quantities will not increase?
(a) The magnetic field at the centre
(b) The magnetic flux linked with the solenoid
(c) The rate of Joule heating
(d)The self—inductance of the solenoid
Answer:
(c) The rate of Joule heating

L = \(\frac{\mu_0 \mathrm{~N}^2 \mathrm{~A}}{l} \mu_r\)
Insertion of iron rod in the solenoid will increase permeabillity of medium. Therefore, magnetic field will increase and this will increase magnetic flux linked as well as the inductance.

Question 32.
A circuit is connected to an AC source of variable frequency. As the frequency of the source is increased, the current first increases and then decreases. Which of the following combinations of elements is likely to comprise the circuit?
(a) L, C and R
(b) L and C
(c) L and R
(d) R and C
Answer:
(a) L, C and R

Question 33.
If n, e, \(\tau\) and ni have their usual meanings, then the resistance of a wire of length l and
cross—sectional area A is given by—
(a) \(\frac{n e^2 \mathrm{~A}}{2 m \tau l}\)
(b) \(\frac{m l}{n e^2 \tau \mathrm{A}}\)
(c) \(\frac{m \tau A}{n e^2 l}\)
(d) \(\frac{n e^2 \tau \mathrm{A}}{2 m l}\)
Answer:
(b) \(\frac{m l}{n e^2 \tau \mathrm{A}}\)

Question 34.
A proton and an alpha particle move in circular orbits in a uniform magnetic field. Their speeds are in the ratio of 9 : 4. The ratio of radii of their circular orbits \(\left(\frac{r_p}{r_{\text {alpha }}}\right)\) is:
(a) \(\frac{3}{4}\)
(b) \(\frac{4}{3}\)
(c) \(\frac{8}{9}\)
(d) \(\frac{9}{8}\)
Answer:
(d) \(\frac{9}{8}\)

Question 35.
A coil of area 100 cm ² is kept at an angle of 300 with a magnetic field of 10 ^-1 T. The magnetic field is reduced to zero in 10 ^-4 s. The induced emf in the coil is —
(a) 5 \(\sqrt{3}\) V
(b) 50 \(\sqrt{3}\) V
(c) 5.0 V
(d) 50.0 V
Answer:
(a) 5 \(\sqrt{3}\) V

Question 36.
A 15 Ω resistor, an 80 mH inductor and a capacitor of capacitance C are connected in series with a 50 Hz ac source. If the source voltage and current in the circuit are in phase, then the value of capacitance is
(a) 100 µF
(b) 127 µF
(c) 142 µF
(d) 160 µF
Answer:
(b) 127 µF

Question 37.
Four objects W, X, Y and Z, each with charge +q are held fixed at four points of a square of side d as shown in the figure.

Objects X and Z are on the midpoints of the sides of the square. The electrostatic force exerted by object W on object X is F. Then the magnitude of the force exerted by object W on Z is
(a) \(\frac{F}{7}\)
(b) \(\frac{F}{5}\)
(c) \(\frac{F}{3}\)
(d) \(\frac{F}{2}\)
Answer:
\(\frac{F}{5}\)

Question 38.
Two sources of equal emf are connected in series. The combination is, in turn connected to an external resistance R. The internal resistance of two sources are r ₁ and r ₂ (r ₂ > r ₁ ). If the potential difference across the source of internal resistance r ₂ is zero, then R equals to —
(a) \(\frac{r_1+r_2}{r_2-r_1}\)
(b) r ₂ – r ₁
(c) \(\frac{r_1 r_2}{r_2-r_1}\)
(d) \(\frac{r_1+r_2}{r_1 r_2}\)
Answer:
(b) r ₂ – r ₁

Question 39.
Which of the following statements is correct?
(a) Magnetic field lines do not form closed loops.
(b) Magnetic field lines start from north pole and end at south pole of a magnet.
(c) The tangent at a point on a magnetic field line represents the direction of the magnetic field at that point.
(d) Two magnetic field lines may intersect each other.
Answer:
(c) The tangent at a point on a magnetic field line represents the direction of the magnetic field at that point.

Question 40.
The equivalent resistance between A and B of the network shown in figure is

(a) 3R Ω
(b) \(\left(\frac{3}{2}\right)\)R Ω
(c) 2R Ω
(d) \(\left(\frac{2}{3}\right)\)R Ω
Answer:
(c) 2R Ω

Question 41.
A bar magnet has magnetic dipole moment \(\overrightarrow{\mathbf{M}}\). Its initial position is parallel to the direction of uniform magnetic field \(\overrightarrow{\mathbf{B}}\). In this position, the magnitudes of torque and force acting on it respectively are —
(a) 0 and MB
(b) MB and MB
(c) 0 and 0
(d) |\(\overrightarrow{\mathbf{M}}\) × \(\overrightarrow{\mathbf{B}}\)| and 0
Answer:
(c) 0 and 0
Magnitude of the torque, \(tau\) = MB sinθ
= MB sinθ …..[∵ θ = 0°
∴ \(tau\) = θ
Force acting on Magnet, PE = MB cos O
PE = MB …[∵ θ = 0
∴ F = 0 ……[uniform magnetic field

Question 42.
Two charge 14 µC and -4 µC are placed at (-12 cm, 0, 0) and (12 cm, 0, 0) in an external electric field E = \(\left(\frac{\mathrm{B}}{r^2}\right)\) where B = 1.2 × 106 N/(cm ² ) and r is in metres. The electrostatic potential energy of the configuration is
(a) 97.9 J
(b) 102.1 J
(c) 2.1 J
(d) -97.9 J
Answer:
(a) 97.9 J

Question 43.
A 300 Ω resistor and a capacitor of \(\left(\frac{25}{\pi}\right)\) µF are connected in series to a 200 V – 50 Hz ac source. The current in the circuit is —
(a) 0.1 A
(b) 0.4 A
(c) 0.6 A
(d) 0.8 A
Answer:
(b) 0.4 A

Question 44.
The core of a transformer is laminated to reduce the effect of
(a) flux leakage
(b) copper loss
(c) hysteresis loss
(d) eddy current
Answer:
(d) eddy current

Question No. 45 to 49 are Assertion (A) and Reason (R) type questions. Given below are the two statements labelled as Assertion (A) and Reason (R). Select the most appropriate answer from the options given below.

(a) Both (A) & (R) are true and (R) is correct explanation of (A).
(b) Both (A) & (R) are true and (R) is not correct explanation of (A).
(c) (A) is true, but (R) is false.
(d) (A) is false and (R) is also false.

Question 45.
Assertion (A) : A negative charge in an electric field moves along the direction of the electric field.
Reason (R) : On a negative charge a force acts in the direction of the electric held.
Answer:
(d) (A) is false and (R) is also false.

Question 46.
Assertion (A) : The poles of a bar magnet cannot be separated.
Reason (R): Magnetic monopoles do not exist.
Answer:
(a) Both (A) & (R) are true and (R) is correct explanation of (A).

Question 47.
Assertion (A) : When radius of a current carrying loop is doubled, its magnetic moment becomes four times.
Reason (R) : The magnetic moment of current carrying loop is directly proportional to the area of the loop.
Answer:
(a) Both (A) & (R) are true and (R) is correct explanation of (A).

Magnetic moment of current carrying loop, M = NIA
∴ M ∝ A
A = πr ² or M ∝ r ²
Hence if r’ = 2r => M’ = 4

Question 48.
Assertion (A) : Higher the range, lower is the resistance of an ammeter.
Reason (R) : To increase the range of an ammeter additionl shunt is added in series to it.
Answer:
(c) (A) is true, but (R) is false.

The lower the resistance of an ammeter gives the higher range. The additional shunt is used in parallel to the galvanometer to increase the range of ammeter. For ideal ammeter, resistance is zero.

Question 49.
Assertion (A) : A step—up transformer cannot be used as a step—down transformer.
Reason (R) : A transformer works only in one direction.
Answer:
(d) (A) is false and (R) is also false.

A transformer is a static electrical device which converts high AC voltage to low and vice-versa. It works on the principle of mutual induction between two windings of coils of transformer. A step-up transformer (N _p < N _s ) can be used as a step-down transformer (N _p > N _s ) by changing their winding of transformer coil.

Section – C

Question 50.
Equipotentials at a large distance from a collèction of charges whose total sum is not zero are —
(a) spheres
(b) planes
(c) ellipsoids
(d) paraboloids
Answer:
(a) spheres

Question 51.
Four charges —q, — q, + q and + q are placed at the corners of a square of side 2 L is shown in figure. The electric potential at point A midway between the two charges + q and + q is

(a) \(\frac{1}{4 \pi \epsilon_0}-\frac{2 q}{\mathrm{~L}}\left(1-\frac{1}{\sqrt{5}}\right)\)
(b) \(\frac{1}{4 \pi \epsilon_0} \frac{2 q}{\mathrm{~L}}\left(1+\frac{1}{\sqrt{5}}\right)\)
(c) \(\frac{1}{4 \pi \epsilon_0} \frac{q}{2 L}\left(1-\frac{1}{\sqrt{5}}\right)\)
(d) zero
Answer:
(a) \(\frac{1}{4 \pi \epsilon_0}-\frac{2 q}{\mathrm{~L}}\left(1-\frac{1}{\sqrt{5}}\right)\)

Case Study:
An experiment was set up with the circuit diagram shown in figure.

Question 52.
The points with the same potential are—
(a) b, c, d
(b) f, h, j
(c) d, e, f
(d) a, b, j
Answer:
(b) f, h, j

Question 53.
The current through branch bg is –
(a) 1 A
(b) \(\frac{1}{3}\)A
(c) \(\frac{1}{2}\)A
(d) \(\frac{2}{3}\)A
Answer:
(c) \(\frac{1}{2}\)A

\(\frac{\varepsilon}{I}\) = R ₁
∴ I = \(\frac{\varepsilon}{\mathrm{R}_1}\) = \(\frac{5}{10}\) = \(\frac{1}{2}\)
∴ I = 0.5A

Question 54.
The power dissipated in R ₁ is –
(a) 2 W
(b) 2.5 W
(c) 3 W
(d) 4.5 W
Answer:
(b) 2.5 W

As we know, P = \(\frac{\mathrm{V}^2}{\mathrm{R}_1}\) = \(\frac{(5)^2}{10}\)
∴ P = \(\frac{25}{10}\) = 2.5 W

Question 55.
The potential difference across R ₃ is —
(a) 1.5V
(b) 2V
(c) 2.5V
(d) 3V
Answer:
(c) 2.5V