Board Paper of Class 12 Physics Term-I 2021 Delhi(SET 4) (Series : SSJ/1)- Solutions

• Question 1
  An electric dipole placed in a non-uniform electric field will experience:
  (a) only a force
  (b) only a torque
  (c) both force and torque
  (d) neither force nor torque VIEW SOLUTION

• Question 2
  Let N₁ be the number of electric field lines going out of an imaginary cube of side a that encloses an isolated point charge 2q and N₂ be the corresponding number for an imaginary sphere of radius a that encloses an isolated point charge 3q. Then (N₁/N₂) is :
  (a) $\frac{1}{\pi }$
  
  (b) $\frac{2}{3}$
  
  (c) $\frac{9}{4}$
  
  (d) π
    VIEW SOLUTION

• Question 3
  In the circuit given below P ≠ R and the reading of the galvanometer is same with switch S open or closed. Then :
  
  (a) I_Q = I_R
  (b) I_R = I_G
  (c) I_P = I_G
  (d) I_Q = I_G
    VIEW SOLUTION

• Question 4
  Two wires A and B, of the same material having length in the ratio 1 : 2 and diameter in the ratio 2 : 3 are connected in series with a battery. The ratio of the potential differences (V_A/V_B) across the two wires respectively is :
  (a) $\frac{1}{3}$
  
  (b) $\frac{3}{4}$
  
  (c) $\frac{4}{5}$
  
  (d) $\frac{9}{8}$ VIEW SOLUTION

• Question 5
  Two moving coil galvanometers G₁ and G₂ have the following particulars respectively :
  N₁ = 30, A₁ = 3.6 × 10^–3 m², B₁ = 0.25 T
  N₂ = 42, A₂ = 1.8 × 10^–3 m², B₂ = 0.50 T
  The spring constant is same for both the galvanometers. The ratio of current sensitivities of G₁ and G₂ is :
  (a) 5 : 7
  (b) 7 : 5
  (c) 1 : 4
  (d) 1 : 1 VIEW SOLUTION

• Question 6
  A current I is flowing through the loop as shown in the figure (MA = R, MB = 2R). The magnetic field at the centre of the loop is $\frac{{\mu }_{0}I}{R}$ times :
  
  (a) $\frac{5}{16}$, into the plane of the paper
  
  (b) $\frac{5}{16}$, out of the plane of the paper
  
  (c) $\frac{7}{16}$, out of the plane of the paper
  
  (d) $\frac{7}{16}$, into the plane of the paper VIEW SOLUTION

• Question 7
  A capacitor and an inductor are connected in two different ac circuits with a bulb glowing in each circuit. The bulb glows more brightly when :
  (a) the number of turns in the inductor is increased
  (b) the separation between the plates of the capacitor is increased
  (c) an iron rod is introduced into the inductor
  (d) a dielectric is introduced into the gap between the plates of the capacitor VIEW SOLUTION

• Question 8
  A pure inductor of 318 mH and a pure resistor of 75 Ω are connected in series to an ac source of 50 Hz. The voltage across 75 Ω resistor is found to be 150 V. The source voltage is :
  (a) 150 V
  (b) 175 V
  (c) 220 V
  (d) 250 V VIEW SOLUTION

• Question 9
  The electric potential at a point on the axis of a short electric dipole, at a distance x from the mid-point of dipole is proportional to :
  (a) $\frac{1}{x^4}$
  
  (b) $\frac{1}{x^{{\displaystyle \frac{3}{2}}}}$
  
  (c) $\frac{1}{x^3}$
  
  (d) $\frac{1}{x^2}$ VIEW SOLUTION

• Question 10
  Let F₁ be the magnitude of the force between two small spheres, charged to a constant potential in free space and F₂ be the magnitude of the force between them in a medium of dielectric constant k. Then $\left(\frac{{\mathrm{F}}_1}{{\mathrm{F}}_2}\right)$ is :
  (a) $\frac{1}{k}$
  
  (b) k
  
  (c) k²
  
  (d) $\frac{1}{k^2}$ VIEW SOLUTION

• Question 11
  Infinity resistance in a resistance box has :
  (a) a resistance of 10⁵ Ω
  (b) a resistance of 10⁷ Ω
  (c) a resistance of ∞ resistance
  (d) a gap only VIEW SOLUTION

• Question 12
  A battery of 15 V and negligible internal resistance is connected across a 50 Ω resistor. The amount of energy dissipated as heat in the resistor in one minute is :
  (a) 122 J
  (b) 270 J
  (c) 420 J
  (d) 720 J VIEW SOLUTION

• Question 13
  Lenz's law is the consequence of the law of conservation of :
  (a) energy
  (b) charge
  (c) mass
  (d) momentum VIEW SOLUTION

• Question 14
  The vertical component of earth's magnetic field at a place is $\left(\frac{1}{\sqrt{3}}\right)$ times the horizontal component. The angle of dip at that place is :
  (a) 0º
  (b) 30º
  (c) 45º
  (d) 60º VIEW SOLUTION

• Question 15
  A long straight wire in the horizontal plane carries a current of 15 A in north to south direction. The magnitude and direction of magnetic field at a point 2.5 m east of the wire respectively are:
  (a) 1·2 μT, vertically upward
  (b) 1·2 μT, vertically downward
  (c) 0·6 μT, vertically upward
  (d) 0·6 μT, vertically downward VIEW SOLUTION

• Question 16
  The emf induced in a 10 H inductor in which current changes from 11 A to 2 A in 9 × 10^–1 s is:
  (a) 10⁴ V
  (b) 10³ V
  (c) 10² V
  (d) 10 V VIEW SOLUTION

• Question 17
  A charge Q is placed at the centre of the line joining two charges q and q. The system of the three charges will be in equilibrium if Q is:
  
  (a) $+\frac{q}{3}$  
  
  (b) $-\frac{q}{3}$
  
  (c) $+\frac{q}{4}$
  
  (d) $-\frac{q}{4}$ VIEW SOLUTION

• Question 18
  Electric flux of an electric field $\overrightarrow{\mathrm{E}}$ through an area $d\overrightarrow{A}$ is given by:
  
  (a) $\overrightarrow{\mathrm{E}}\times d\overrightarrow{\mathrm{A}}$
  
  (b) $\frac{\overrightarrow{\mathrm{E}}\times d\overrightarrow{\mathrm{A}}}{{\mathrm{\epsilon }}_0}$
  
  (c) $\overrightarrow{\mathrm{E}} . d\overrightarrow{\mathrm{A}}$
  
  (d) $\frac{\overrightarrow{\mathrm{E}} . d\overrightarrow{\mathrm{A}}}{{\mathrm{\epsilon }}_0}$ VIEW SOLUTION

• Question 19
  In a potentiometer experiment, the balancing length with a cell is 120 cm. When the cell is shunted by a 1 Ω resistance, the balancing length becomes 40 cm. The internal resistance of the cell is:
  (a) 10 Ω
  (b) 7 Ω
  (c) 3 Ω
  (d) 2 Ω VIEW SOLUTION

• Question 20
  An electron is projected with velocity $\overrightarrow{v}$ along the axis of a current carrying long solenoid. Which one of the following statements is true?
  (a) The path of the electron will be circular about the axis.
  (b) The electron will be accelerated along the axis.
  (c) The path of the electron will be helical.
  (d) The electron will continue to move with the same velocity $\overrightarrow{v}$ along the axis of the solenoid. VIEW SOLUTION

• Question 21
  If the speed v of a charged particle moving in a magnetic field $\overrightarrow{\mathrm{B}}$ ($\overrightarrow{v}$ is perpendicular to $\overrightarrow{\mathrm{B}}$) is halved, then the radius of its path will
  (a) not change
  (b) become two times
  (c) become one-fourth
  (d) become half VIEW SOLUTION

• Question 22
  A metal plate is getting heated. Which one of following statements is incorrect?
  (a) It is placed in a space varying magnetic field that does not vary with time.
  (b) A direct current is passing through the plate.
  (c) An alternating current is passing through the plate.
  (d) It is placed in a time varying magnetic field. VIEW SOLUTION

• Question 23
  In an ac circuit the applied voltage and resultant current are $E=E_0\sin \omega t$ and I = I₀ sin$\left(\omega t+\frac{\mathrm{\pi }}{2}\right)$ respectively. The average power consumed in the circuit is:
  (a) E₀I₀ 
  
  (b) $\frac{{\mathrm{E}}_0{\mathrm{I}}_0}{2}$
  
  (c) $\frac{{\mathrm{E}}_0{\mathrm{I}}_0}{\sqrt{2}}$
  
  (d) Zero VIEW SOLUTION

• Question 24
  The speed acquired by a free electron when accelerated from rest through a potential difference of 100 V is: 
  (a) 6 × 10⁶ ms^–1 
  (b) 3 × 10⁶ ms^–1 
  (c) 4 × 10⁵ ms^–1
  (d) 2 × 10³ ms^–1 VIEW SOLUTION

• Question 25
  Which one of the following is not affected by the presence of a magnetic field?
  (a) A current carrying conductor
  (b) A moving charge
  (c) A stationary charge
  (d) A rectangular current loop with its plane parallel to the field VIEW SOLUTION