Moving Charges & Magnetism PYQs Set 5 (PDF)

Set 5 of 17 · Questions 121-150 of 499

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Mere Teacher · Previous Year Questions NEET Physics · Moving Charges & Magnetism · Set 5 (Q121-150)
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121. $A square loop is carrying a steady current I and the magnitude of its magnetic dipole moment is m If this square loop is changed to a circular loop and it carries the same current, the magnitude of the magnetic dipole moment of circular loop will be:$ (1) $\frac{m}{π}$ (2) $\frac{3 m}{π}$ (3) $\frac{2 m}{π}$ (4) $\frac{4 m}{π}$ 122. $When a charged particle moving with velocity v is subjected to a magnetic field of induction B, the force on it is non‐zero. This implies that$ (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) $angle between can have any value other than zero and 18 0^{o} .$ 123. $Two particles X and Y having equal charges after being accelerated through same potential difference enter a region of uniform magnetic field and describe a circular paths of radii r_{1} and r_{2} respectively. The ratio of the mass of X to that of Y is$ (1) $\frac{r _{1}}{r _{2}}$ (2) $\frac{r _{1}}{r _{2}}$ (3) $(\frac{r _{2}}{r _{1}})^{2}$ (4) $(\frac{r _{1}}{r _{2}})^{2}$ 124. $A straight wire of length 2 m carries a current of 10 A, If this wire is placed in a uniform magnetic field of 0.15 T making an angle of 45^{\circ} with the magnetic field, the applied force on the wire will be$ (1) $1.5 N$ (2) $3 N$ (3) $32 N$ (4) $\frac{3}{2} N$ 125. $A particle having the same charge as of electron moves in a circular path of radius 0.5 cm under the influence of a magnetic field of 0.5 T . If an electric field of 100 \frac{V}{m} makes it to move in a straight path then the mass of the particle is (Given charge of electron (= 1.6 \times 10^{- 19} C)$ (1) $9.1 \times 10^{- 31} kg$ (2) $1.6 \times 10^{- 27} kg$ (3) $1.6 \times 10^{- 19} kg$ (4) $2.0 \times 10^{- 24} kg$ 126. $The magnetic field at a point p situated at perpendicular distance ' R' from a long straight wire carrying a current of 12 A is 3 \times 10^{- 5} Wb / m^{2} . The value of ' R' in mm is (μ_{0} = 4 π \times 10^{- 7} Wb / Am)$ (1) $0.08$ (2) $0.8$ (3) $8$ (4) $80$ 127. $The current passing through a conducting loop in the form of equilateral triangle of side 43 cm is 2 A. The magnetic field at its centroid is α \times 10^{- 5} T . The value of α is____- (Given : μ_{o} = 4 π \times 10^{- 7} SI units)$ (1) $23$ (2) $\frac{3}{2}$ (3) $33$ (4) $3$ 128. $An electron is moving in a circular path under the influence of a transverse magnetic field of 3.57 \times 1 0^{-2} T. If the value of e/m is 1.76 \times 1 0^{11} C/kg, the frequency of revolution of the electron is:$ (1) $6.82 MHz$ (2) $1 GHz$ (3) $100 MHz$ (4) $62.8 MHz$ 129. $The correct Biot-Savart law in vector form is$ (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) $d B = \frac{μ _{0}}{4 π} \frac{Id l}{r ^{3}}$ 130. $A coil carrying electric current is placed in uniform magnetic field$ (1) $torque is formed$ (2) $e.m.f is induced$ (3) $both(a) and (b) are correct$ (4) $none of these$ 131. $An electron is moving in a circle of radius r in a uniform magnetic field B . Suddenly the field is reduced to B /2 . The radius of the circular path now becomes$ (1) $r /2$ (2) $2 r$ (3) $r /4$ (4) $4 r$ 132. $Under the influence of a uniform magnetic field, a charged particle moves with a constant speed v in a circle of radius R . The time period of rotation of the particle$ (1) $depends on R and not on v$ (2) $is independent of both v and R$ (3) $depends on both v and R$ (4) $depends on v and not on R .$ 133. $Force acting on an electron moving with velocity v in a magnetic field B is (is the charge of electron)$ (1) $e (v \times B)$ (2) $e (v \cdot B)$ (3) $e \frac{v}{B}$ (4) $e \frac{B}{v}$ 134. $A metallic rod of mass per unit length 0.5 kg m^{- 1} is lying horizontally on a smooth inclined plane which makes an angle of 30^{\circ} with the horizontal. A magnetic field of strength 0.25 T is acting on it in the vertical direction. When a current ' I' is flowing through it, the rod is not allowed to slide down. The quantity of current required to keep the rod stationary is$ (1) $14.76 A$ (2) $7.14 A$ (3) $11.32 A$ (4) $5.98 A$ 135. $The magnetic moment of electron due to orbital motion is proportional to (n = principle quantum number)$ (1) $1 n^{2}$ (2) $\frac{1}{n}$ (3) $n^{2}$ (4) $n$ 136. $In a crossed field, the magnetic field induction is 2.0 T and electric field intensity is 20 \times 10^{3} V / m . At which velocity the electron will travel in a straight line without the effect of electric and magnetic fields?$ (1) $\frac{20}{16} \times 10^{3} ms^{- 1}$ (2) $10 \times 10^{3} ms^{- 1}$ (3) $20 \times 10^{3} ms^{- 1}$ (4) $40 \times 10^{3} ms^{- 1}$ 137. $A charge q is accelerated through a potential difference V . It is then passed normally through a uniform magnetic field, where it moves in a circle of radius r . The potential difference required to move it in a circle of radius 2 r is$ (1) $2 V$ (2) $4 V$ (3) $1 V$ (4) $3 V$ 138. $A gyromagnetic ratio of the electron revolving in a circular orbit of hydrogen atom is 8.8 \times 10^{10} C kg^{- 1} . What is the mass of the electron? Given charge of the electron = 1.6 \times 10^{- 19} C .$ (1) $1.1\times 1 0^{- 29} kg$ (2) $1 \times 10^{- 29} kg$ (3) $\frac{1}{11} \times 1 0^{- 29} kg$ (4) $0.1\times 1 0^{- 29} kg$ 139. $A long solenoid has 70 turns / cm and carries current I . An electron moves within the solenoid in a circle of radius 2.5 cm perpendicular to the solenoid axis. If the speed of the electron is 4.4 \times 10^{6} m / s then the current I in the solenoid is(Take μ_{0} = 4 π \times 10^{- 7} SI unit, mass of electron = 9 \times 10^{- 31} kg, charge of electron = 1.6 \times 10^{- 19} C)$ (1) $98.5 mA$ (2) $112.5 mA$ (3) $125 mA$ (4) $175.0 mA$ 140. $A square current carrying loop is suspended in a uniform magnetic field acting in the plane of the loop. If the force on one arm of the loop is F . the net force on the remaining three arms of the loop is$ (1) $3 F$ (2) $- F$ (3) $- 3 F$ (4) $F .$ 141. $A solenoid of length 50 cm having 100 turns carries a current of 2.5 A . The magnetic field at one end of the solenoid is$ (1) $1.57 \times 10^{- 4} T$ (2) $3.14 \times 10^{- 4} T$ (3) $9.42 \times 10^{- 4} T$ (4) $6.28 \times 10^{- 4} T$ 142. $A solenoid of 1200 turns is wound uniformly in a single layer on a glass tube 2 m long and 0.2 m in diameter. The magnetic intensity at the center of the solenoid when a current of 2 A flows through it is:$ (1) $2.4 x l 0^{3} A m^{- 1}$ (2) $1.2 x 1 0^{3} A m^{- 1}$ (3) $1 A m^{- 1}$ (4) $2.4 x 1 0^{- 3} A m^{- 1}$ 143. $A current carrying coil is subjected to a uniform magnetic field. The coil will orient so that its plane becomes$ (1) $inclined at 4 5^{o} to the magnetic field$ (2) $inclined at any arbitrary angle to the magnetic field$ (3) $parallel to the magnetic field$ (4) $perpendicular to magnetic field.$ 144. $Consider a tightly wound 100 turn coil of radius 10 cm carrying a current of 2 A . The magnitude of the magnetic field at the centre of the coil is$ (1) $3.14 \times 10^{- 4} T$ (2) $6.28 \times 10^{- 4} T$ (3) $12.56 \times 10^{- 4} T$ (4) $0$ 145. $A magnetic needle suspended parallel to a magnetic field requires 3 J of work to turn it through 60°. The torque needed to maintain the needle in this position will be:$ (1) $23 J$ (2) $3J$ (3) $3 J$ (4) $\frac{3}{2} J$ 146. $Magnetic field at a distance r from an infinitely long straight conductor carrying a steady current varies as$ (1) $\frac{1}{r ^{2}}$ (2) $\frac{1}{r}$ (3) $\frac{1}{r ^{3}}$ (4) $\frac{1}{r}$ 147. $The work done in turning a magnet of magnetic moment M by an angle of 9 0^{o} from the meridian, is n times the corresponding work done to turn it through an angle of 6 0^{o} . The value of n is given by$ (1) $1/2$ (2) $1/4$ (3) $2$ (4) $1$ 148. $A proton carrying 1 MeV kinetic energy is moving in a circular path of radius R in uniform magnetic field. What should be the energy of an α ‐particle to describe a circle of same radius in the same field?$ (1) $2 MeV$ (2) $1 MeV$ (3) $0.5 MeV$ (4) $4 MeV$ 149. $A strong magnetic field is applied on a stationary electron. Then the electron$ (1) $moves in the direction of the field.$ (2) $moves in an opposite direction of the field.$ (3) $remains stationary.$ (4) $starts spinning.$ 150. $A long straight wire carries a current of 18A. The magnitude of the magnetic field at a point 12 cm from it is$ (1) $1.5 \times 10^{- 5} T$ (2) $2 \times 10^{- 5} T$ (3) $3 \times 10^{- 5} T$ (4) $1.8 \times 10^{- 5} T$