Moving Charges & Magnetism PYQs Set 5 (PDF)

Set 5 of 19 · Questions 121-150 of 549

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Mere Teacher · Previous Year Questions JEE Main Physics · Moving Charges & Magnetism · Set 5 (Q121-150)
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121. $A cyclotron's oscillator frequency is 10 MHz and the operating magnetic field is 0.66 T . If the radius of its dees is 60 cm, then the kinetic energy of the proton beam produced by the accelerator is$ (1) $9 MeV$ (2) $10 MeV$ (3) $7 MeV$ (4) $11 MeV$ 122. $A long straight wire of radius a carries a steady current I. The current is uniformly distributed over its cross-section. The ratio of the magnetic fields B and B, at a radial distances a/2 and 2a respectively, from the axis of the wire is:$ (1) $4$ (2) $\frac{1}{4}$ (3) $\frac{1}{2}$ (4) $1$ 123. $A range of galvanometer is ' V', when 50Ω resistance is connected in series. Its range gets doubled when 500Ω resistance is connected in series. Galvanometer resistance is$ (1) $100Ω$ (2) $200Ω$ (3) $300Ω$ (4) $400Ω$ 124. $A long straight wire of radius a carries a steady current I . The current is uniformly distributed over its cross‐section. The ratio of the magnetic fields B and B^{’}, at radial distances a /2 and 2 a respectively, from the axis of the wire is$ (1) $1$ (2) $4$ (3) $\frac{1}{4}$ (4) $\frac{1}{2}$ 125. $A galvanometer has a deflection of 25 divisions for a current of 0.1 A flowing through it. Then the current sensitivity of the galvanometer is$ (1) $25 div / A$ (2) $250 div/A$ (3) $2.5 div / A$ (4) $0.25 div / A$ 126. $Magnetic field at the centre of a circular coil of radius R due to current I flowing through it is B . The magnetic field at a point along the axis at distance R from the centre is$ (1) $\frac{B}{2}$ (2) $\frac{B}{4}$ (3) $\frac{B}{8}$ (4) $8 b$ 127. $Two long parallel conducting wires carrying currents are separated by a distance ' x'. Work done per unit length in changing the distance between the wires is proportional to$ (1) $\frac{1}{l o g _{e} x}$ (2) $\frac{1}{x}$ (3) $log_{e} x$ (4) $x$ 128. $The electric field of a plane electromagnetic wave is given by E \to= E_{o} \frac{i ^ + j ^}{2} cos (kz + ωt) . At t = 0, a positively charged particle is at the point (x, y, z) = (0, 0, \frac{π}{k}) . If its instantaneous velocity at (t = 0) is v_{o} k^, the force acting on it due to the wave is :$ (1) $f = 0$ (2) $Antiparallel to \frac{i ^ + j ^}{2}$ (3) $Parallel to \frac{i ^ + j ^}{2}$ (4) $k^$ 129. $A proton and an α-particle (with their masses in the ration of 1 : 4 and charges in the ration of 1 : 2) are accelerated from rest through a potential difference V. If a uniform magnetic field (B) is set up perpendicular to their velocities, the ratio of the radii r_{p} : r_{α} of the circular paths described by them will be:$ (1) $1 : 3$ (2) $1 : 3$ (3) $1 : 2$ (4) $1 : 2$ 130. $Two parallel wires in free space are 10 cm apart and each carries a current of 10 A in the same direction. The force exerted by one wire on the other (per unit length) is$ (1) $2\times 1 0^{- 4} N m-1 [attractive]$ (2) $2\times 1 0^{- 7} N m-1 [attractive]$ (3) $2\times 1 0^{- 4} N m-1 [repulsive]$ (4) $2\times 1 0^{- 7} N m-1 [repulsive]$ 131. $Two parallel conductor each 50 m long, separated by 0.2 m experience a force of 1 N . If the current in the first conductor is twice that of the second conductor, then what is the current in the second conductor? (μ_{0} = 4 π \times 10^{- 7})$ (1) $100 A$ (2) $200 A$ (3) $120 A .$ (4) $50 A$ 132. $A square loop is carrying a steady current I and the magnitude of its magnetic dipole moment is m If this square loop is changed to a circular loop and it carries the same current, the magnitude of the magnetic dipole moment of circular loop will be:$ (1) $\frac{m}{π}$ (2) $\frac{3 m}{π}$ (3) $\frac{2 m}{π}$ (4) $\frac{4 m}{π}$ 133. $When a charged particle moving with velocity v is subjected to a magnetic field of induction B, the force on it is non‐zero. This implies that$ (1) $angle between is either zero or 18 0^{o}$ (2) $angle between is necessarily 9 0^{o}$ (3) $angle between can have any value other than 9 0^{o}$ (4) $angle between can have any value other than zero and 18 0^{o} .$ 134. $Two particles X and Y having equal charges after being accelerated through same potential difference enter a region of uniform magnetic field and describe a circular paths of radii r_{1} and r_{2} respectively. The ratio of the mass of X to that of Y is$ (1) $\frac{r _{1}}{r _{2}}$ (2) $\frac{r _{1}}{r _{2}}$ (3) $(\frac{r _{2}}{r _{1}})^{2}$ (4) $(\frac{r _{1}}{r _{2}})^{2}$ 135. $A straight wire of length 2 m carries a current of 10 A, If this wire is placed in a uniform magnetic field of 0.15 T making an angle of 45^{\circ} with the magnetic field, the applied force on the wire will be$ (1) $1.5 N$ (2) $3 N$ (3) $32 N$ (4) $\frac{3}{2} N$ 136. $A particle having the same charge as of electron moves in a circular path of radius 0.5 cm under the influence of a magnetic field of 0.5 T . If an electric field of 100 \frac{V}{m} makes it to move in a straight path then the mass of the particle is (Given charge of electron (= 1.6 \times 10^{- 19} C)$ (1) $9.1 \times 10^{- 31} kg$ (2) $1.6 \times 10^{- 27} kg$ (3) $1.6 \times 10^{- 19} kg$ (4) $2.0 \times 10^{- 24} kg$ 137. $The magnetic field at a point p situated at perpendicular distance ' R' from a long straight wire carrying a current of 12 A is 3 \times 10^{- 5} Wb / m^{2} . The value of ' R' in mm is (μ_{0} = 4 π \times 10^{- 7} Wb / Am)$ (1) $0.08$ (2) $0.8$ (3) $8$ (4) $80$ 138. $The current passing through a conducting loop in the form of equilateral triangle of side 43 cm is 2 A. The magnetic field at its centroid is α \times 10^{- 5} T . The value of α is____- (Given : μ_{o} = 4 π \times 10^{- 7} SI units)$ (1) $23$ (2) $\frac{3}{2}$ (3) $33$ (4) $3$ 139. $An electron is moving in a circular path under the influence of a transverse magnetic field of 3.57 \times 1 0^{-2} T. If the value of e/m is 1.76 \times 1 0^{11} C/kg, the frequency of revolution of the electron is:$ (1) $6.82 MHz$ (2) $1 GHz$ (3) $100 MHz$ (4) $62.8 MHz$ 140. $The correct Biot-Savart law in vector form is$ (1) $d B = \frac{μ _{0}}{4 π} \frac{I ( d l \times r )}{r ^{2}}$ (2) $d B = \frac{μ _{0}}{4 π} \frac{I ( d l \times r )}{r ^{3}}$ (3) $d B = \frac{μ _{0}}{4 π} \frac{Id l}{r ^{2}}$ (4) $d B = \frac{μ _{0}}{4 π} \frac{Id l}{r ^{3}}$ 141. $A coil carrying electric current is placed in uniform magnetic field$ (1) $torque is formed$ (2) $e.m.f is induced$ (3) $both(a) and (b) are correct$ (4) $none of these$ 142. $An electron is moving in a circle of radius r in a uniform magnetic field B . Suddenly the field is reduced to B /2 . The radius of the circular path now becomes$ (1) $r /2$ (2) $2 r$ (3) $r /4$ (4) $4 r$ 143. $Under the influence of a uniform magnetic field, a charged particle moves with a constant speed v in a circle of radius R . The time period of rotation of the particle$ (1) $depends on R and not on v$ (2) $is independent of both v and R$ (3) $depends on both v and R$ (4) $depends on v and not on R .$ 144. $Force acting on an electron moving with velocity v in a magnetic field B is (is the charge of electron)$ (1) $e (v \times B)$ (2) $e (v \cdot B)$ (3) $e \frac{v}{B}$ (4) $e \frac{B}{v}$ 145. $A metallic rod of mass per unit length 0.5 kg m^{- 1} is lying horizontally on a smooth inclined plane which makes an angle of 30^{\circ} with the horizontal. A magnetic field of strength 0.25 T is acting on it in the vertical direction. When a current ' I' is flowing through it, the rod is not allowed to slide down. The quantity of current required to keep the rod stationary is$ (1) $14.76 A$ (2) $7.14 A$ (3) $11.32 A$ (4) $5.98 A$ 146. $The magnetic moment of electron due to orbital motion is proportional to (n = principle quantum number)$ (1) $1 n^{2}$ (2) $\frac{1}{n}$ (3) $n^{2}$ (4) $n$ 147. $If the maximum value of accelerating potential provided by a ratio frequency oscillator is 12kV. The number of revolution made by a proton in a cyclotron to achieve one sixth of the speed of light is (m_{p} = 1.67 \times 1 0^{- 27} kg, e = 1.6 \times 1 0^{- 19} C Speed of light = 3 \times 1 0^{8} m / s)$ 148. $A 2 A current carrying straight metal wire of resistance 1Ω, resistivity 2 \times 10^{- 6} Ωm, area of cross-section 10 mm^{2} and mass 500 g is suspended horizontally in mid air by applying a uniform magnetic field B . The magnitude of B is_____\times 10^{- 1} T (given, g = 10 m / s^{2}).$ 149. $A 4.0 cm long straight wire carrying a current of 8 A is placed perpendicular to a uniform magnetic field of strength 0.15 T. The magnetic force on the wire is mN.$ 150. $The magnetic intensity at the centre of a long current carrying solenoid is found to be 1. 6 x 1 0^{3} A m^{- 1} . If the number of turns is 8 per cm, then the current flowing through the solenoid is______A.$