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# Board Paper of Class 12 Physics Term-I 2021 Delhi(SET 4) (Series: SSJ/2)- Solutions

General Instructions:

(i) This question paper contains 55 questions out of which 45 questions are to be attempted. All questions carry equal marks.

(ii) The question paper consists of three Sections - Section A, B and C.

(iii) Section - A contains 25 questions. Attempt any 20 questions from Q. No. 01 to 25.

(iv) Section - B contains 24 questions. Attempt any 20 questions from Q. No. 26 to 49.

(v) Section - C contains 6 questions. Attempt any 5 questions from Q. No. 50 to 55.

(vi) The first 20 Questions attempted in Section - A & Section - B and first 5 questions attempted in

Section - C by a candidate will be evaluated.

(vii) There is only one correct option for every multiple choice question (MCQ).

Marks will not be awarded for answering more than one option.

(viii) There is no negative marking.

• 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

VIEW SOLUTION

• Question 2
In an experiment three microscopic latex spheres are sprayed into a chamber and became charged with charges +3e, +5e and –3e 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?
(a) +5e, –4e, +5e
(b) +6e, +6e, –7e
(c) –4e, +3.5e, +5.5e
(d) +5e, –8e, +7e VIEW SOLUTION

• Question 3
An object has charge of 1 C and gains 5.0 × 1018 electrons. The net charge on the object becomes-
(a) –0.80 C
(b) +0.80 C
(c) +1.80 C
(d) +0.20 C VIEW SOLUTION

• Question 4
Kirchhoff's first rule ∑I = 0 and second rule ∑IR = ∑E (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 charges
(c) conservation of charge, conservation of momentum
(d) conservation of charge, conservation of energy VIEW SOLUTION

• 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 VIEW SOLUTION

• Question 6
Which of the following has negative temperature coefficient of resistivity?
(a) metal
(b) metal and semiconductor
(c) semiconductor
(d) metal and alloy VIEW SOLUTION

• Question 7
Two wires carrying currents I1 and I2 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 VIEW SOLUTION

• 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 VIEW SOLUTION

• 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 VIEW SOLUTION

• Question 10
The magnetic field at the centre of a current carrying circular loop of radius R, is B1. The magnetic field at a point on its axis at a distance R from the center of the loop is B2. Then the ratio (B1/B2) is

(a) $2\sqrt{2}$

(b) $\frac{1}{\sqrt{2}}$

(c) $\sqrt{2}$

(d) 2 VIEW SOLUTION

• 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 VIEW SOLUTION

• Question 12
The rms current in a circuit connected to a 50 Hz ac source is 15 A. The value of the current in the circuit $\left(\frac{1}{600}\right)$s after the instant the current is zero, is–

(a)

(b)

(c)

(d) 8 A VIEW SOLUTION

• Question 13
In a circuit the phase difference between the alternating current and the source voltage is $\frac{\mathrm{\pi }}{2}$. 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 VIEW SOLUTION

• Question 14
The electric potential V at any point (x, y, z) is given by V = 3x2 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 VIEW SOLUTION

• 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?
(a)
(b)
(c)
(d)  VIEW SOLUTION

• 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 × 10–2J. The value of X is –
(a) 1 μF
(b) 2 μF
(c) 3 μF
(d) 4 μF VIEW SOLUTION

• 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 × 1019
(b) 2.5 × 1018
(c) 1.25 × 1018
(d) 2.5 × 1016 VIEW SOLUTION

• Question 18
The impedance of a series LCR circuit is–
(a) R + XL + XC

(b) $\sqrt{\frac{1}{{\mathrm{X}}_{\mathrm{C}}^{2}}+\frac{1}{{\mathrm{X}}_{\mathrm{L}}^{2}}+{\mathrm{R}}^{2}}$

(c) $\sqrt{{\mathrm{X}}_{\mathrm{L}}^{2}-{\mathrm{X}}_{\mathrm{C}}^{2}+{\mathrm{R}}^{2}}$

(d) $\sqrt{{\mathrm{R}}^{2}+{\left({\mathrm{X}}_{\mathrm{L}}-{\mathrm{X}}_{\mathrm{C}}\right)}^{2}}$ VIEW SOLUTION

• Question 19

When an alternating voltage  is applied to a circuit, a current $\mathrm{I}={\mathrm{I}}_{0}\mathrm{sin}\left(\mathrm{\omega t}+\frac{\mathrm{\pi }}{2}\right)$ flows through it. The average power dissipated in the circuit is
(a) ${\mathrm{E}}_{\mathrm{rms}}·{\mathrm{I}}_{\mathrm{rms}}$

(b) ${\mathrm{E}}_{0}{\mathrm{I}}_{0}$

(c) $\frac{{\mathrm{E}}_{0}{\mathrm{I}}_{0}}{\sqrt{2}}$

(d) Zero

VIEW SOLUTION

• 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 VIEW SOLUTION

• 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) 65 V VIEW SOLUTION

• 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 VIEW SOLUTION

• 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 $\frac{r}{2}\left(r>>R\right)$ will be
(a) $\frac{E}{4}$

(b) 0

(c) 2E

(d) 4E
VIEW SOLUTION

• Question 24
The horizontal component of earth's magnetic field at a place is 0.2 G whereas it's total magnetic field is 0.4 G. The angle of dip at the place is
(a) 30°
(b) 45°
(c) 60°
(d) 90° VIEW SOLUTION

• 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 VIEW SOLUTION

• Question 26
A square sheet of side ‘a' is lying parallel to XY plane at z = a. The electric field in the region is . The electric flux through the sheet is

(a) a4c

(b) $\frac{1}{3}{a}^{3}c$

(c) $\frac{1}{3}{a}^{4}c$

(d) 0
VIEW SOLUTION

• Question 27
Three charges q, –q and q0, are placed as shown in figure. The magnitude of the net force on the charge q0 at point O is $\left[k=\frac{1}{\left(4\mathrm{\pi }{\in }_{0}\right)}\right]$

(a) 0

(b) $\frac{2kq{q}_{0}}{{a}^{2}}$

(c) $\frac{\sqrt{2}kq{q}_{0}}{{a}^{2}}$

(d) $\frac{1}{\sqrt{2}}\frac{kq{q}_{0}}{{a}^{2}}$ VIEW SOLUTION

• Question 28
A + 3.0 nC charge Q is initially at rest at a distance of r1 = 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 r2 = 15 cm. In this process work done by the field is
(a) 1.29 × 10–5 J
(b) 3.6 × 105 J
(c) –4.5 × 10–7 J
(d) 4.5 × 10–7 J VIEW SOLUTION

• Question 29
A car battery is charged by a 12 V supply, and energy stored in it is 7.20 × 105 J. The charge passed through the battery is -
(a) 6.0 × 104 C
(b) 5.8 × 103 J
(C) 8.64 × 106 J
(d) 1.6 × 105 C VIEW SOLUTION

• 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) $\frac{mgB}{l}$

(b) $\frac{mgl}{B}$

(c) $\frac{mg}{lB}$

(d) $\frac{lB}{mg}$ VIEW SOLUTION

• Question 31
A constant current is flowing through a solenoid. An iron road 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 heating
(d) The self-inductance of the solenoid VIEW SOLUTION

• 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 VIEW SOLUTION

• Question 33
If n, e, $\tau$ and m have their usual meanings, then the resistance of a wire of length l and cross-sectional area A is given by –

(a) $\frac{{\mathrm{ne}}^{2}\mathrm{A}}{2\mathrm{m\tau }l}$

(b) $\frac{\mathrm{m}l}{{\mathrm{ne}}^{2}\mathrm{\tau A}}$

(c) $\frac{\mathrm{m\tau A}}{{\mathrm{ne}}^{2}l}$

(d) $\frac{{\mathrm{ne}}^{2}\mathrm{\tau A}}{2\mathrm{m}l}$ VIEW SOLUTION

• 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 $\left(\frac{{\mathrm{r}}_{\mathrm{p}}}{{\mathrm{r}}_{\mathrm{alpha}}}\right)$ is
(a) $\frac{3}{4}$

(b) $\frac{4}{3}$

(c) $\frac{8}{9}$

(d) $\frac{9}{8}$ VIEW SOLUTION

• Question 35
A coil of area 100 cm2 is kept at an angle of 30° 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)

(b)

(c)

(d)  VIEW SOLUTION

• Question 36
A 15 $\mathrm{\Omega }$ 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 $\mathrm{\mu }$F
(b) 127 $\mathrm{\mu }$F
(c) 142 $\mathrm{\mu }$F
(d) 160 $\mathrm{\mu }$F VIEW SOLUTION

• 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) $\frac{F}{2}$ VIEW SOLUTION

• Question 38
Two sources of equal emf are connected in series. This combination is, in turn connected to an external resistance R. The internal resistance of two sources are r1 and r2 (r2 > r1). If the potential difference across the source of internal resistance r2 is zero, then R equals to –
(a) $\frac{{r}_{1}+{r}_{2}}{{r}_{2}-{r}_{1}}$

(b) r2r1

(c) $\frac{{r}_{1}{r}_{2}}{{r}_{2}-{r}_{1}}$

(d)

VIEW SOLUTION

• 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. VIEW SOLUTION

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

(a) 3R $\mathrm{\Omega }$

(b)

(c) 2R $\mathrm{\Omega }$

(d)  VIEW SOLUTION

• Question 41
A bar magnet has magnetic dipole moment $\stackrel{\to }{\mathrm{M}}$. Its initial position is parallel to the direction of uniform magnetic field $\stackrel{\to }{\mathrm{B}}$. 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) $\left|\stackrel{\to }{\mathrm{M}}×\stackrel{\to }{\mathrm{B}}\right|$ and 0 VIEW SOLUTION

• Question 42
Two charges 14 μC and –4 μC are placed at (–12 cm, 0, 0) and (12 cm, 0, 0) in an external electric field E = $\left(\frac{B}{{r}^{2}}\right)$, where B = 1.2 × 10N/(cm2) 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 VIEW SOLUTION

• Question 43
A 300 Ω resistor and a capacitor of $\left(\frac{25}{\mathrm{\pi }}\right)$ 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 VIEW SOLUTION

• 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 VIEW SOLUTION

• Question 45
The question consists of two statements – Assertion (A) and Reason (R).
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 field.
Select the appropriate option 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.
VIEW SOLUTION

• Question 46
The question consists of two statements – Assertion (A) and Reason (R).
Assertion (A): The poles of a magnet cannot be separated.
Reason (R): Magnetic monopoles do not exist.
Select the appropriate option 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. VIEW SOLUTION

• Question 47
The question consists of two statements – Assertion (A) and Reason (R).
Assertion (A): When radius of a current carrying loop is doubled, its magnetic moment becomes four times.
Reason (R): The magnetic moment of a current carrying loop is directly proportional to the area of the loop.
Select the appropriate option 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. VIEW SOLUTION

• Question 48
The question consists of two statements – Assertion (A) and Reason (R).
Assertion (A): Higher the range, lower is the resistance of an ammeter.
Reason (R): To increase the range of an ammeter additional shunt is added in series to it.
Select the appropriate option 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.
VIEW SOLUTION

• Question 49
The question consists of two statements – Assertion (A) and Reason (R).
Assertion (A): A step-up transformer cannot be used as a step-down transformer.
Reason (R): A transformer works only in one direction.
Select the appropriate option 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. VIEW SOLUTION

• Question 50
Equipotentials at a large distance from a collection of charges whose total sum is not zero are–
(a) spheres
(b) planes
(c) ellipsoids
(d) paraboloids
VIEW SOLUTION

• 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) $\frac{1}{4\mathrm{\pi }{\in }_{0}}\frac{2q}{\mathrm{L}}\left(1-\frac{1}{\sqrt{5}}\right)$
(b) $\frac{1}{4\mathrm{\pi }{\in }_{0}}\frac{2q}{\mathrm{L}}\left(1+\frac{1}{\sqrt{5}}\right)$
(c)
(d) zero VIEW SOLUTION

• Question 52
Case Study:
An experiment was set up with the circuit diagram shown in figure.
Given that R1 = 10 Ω, R2 = R3 = 5 Ω, r = 0 Ω and E = 5 V

The points with the same potential are-
(a) b, c, d
(b) f, h, j
(c) d, e, f
(d) a, b, j VIEW SOLUTION

• Question 53
Case Study:
An experiment was set up with the circuit diagram shown in figure.
Given that R1 = 10 Ω, R2 = R3 = 5 Ω, r = 0 Ω and E = 5 V

The current through branch bg is-
(a) 1 A

(b) $\frac{1}{3}\mathrm{A}$

(c) $\frac{1}{2}\mathrm{A}$

(d) $\frac{2}{3}\mathrm{A}$ VIEW SOLUTION

• Question 54
Case Study:
An experiment was set up with the circuit diagram shown in figure.
Given that R1 = 10 Ω, R2 = R3 = 5 Ω, r = 0 Ω and E = 5 V

The power dissipated in R1 is-
(a) 2 W
(b) 2.5 W
(c) 3 W
(d) 4.5 W VIEW SOLUTION

• Question 55
Case Study:
An experiment was set up with the circuit diagram shown in figure.
Given that R1 = 10 Ω, R2 = R3 = 5 Ω, r = 0 Ω and E = 5 V

The potential difference across R3 is-
(a) 1.5 V
(b) 2 V
(c) 2.5 V
(d) 3 V VIEW SOLUTION
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