Moving Charges And Magnetism

A rectangular coil of area A, having number of turns N is rotated at f revolutions per second in a uniform magnetic field B. The maximum emf induced in the coil is

• $2 \mathrm{\pi }$fNB

• 2fNBA

• $2 \mathrm{\pi }$fBA

• $2 \mathrm{\pi }$fNBA

An electron having mass 9.1 x 10^-31 kg moves in a circular path of radius 0.4 m with velocity 10⁵ m/s in a magnetic field. The strength of magnetic field is

• 1.56 × 10^-5 T

• 1.62 × 10^-4 T

• 1.42 x 10^-6 T

• 1.88 × 10^-5 T

A current of 0.4 A is passed through the coil of galvanometer having 500 turns and each turn has an average area of 3 x 10^-4 m² . If a torque of 2 Nm is required for this coil carrying some current to set it parallel to a magnetic field then the strength of magnetic field will be

• 31 T

• 33.34 T

• 32 T

• 40 T

A galvanometer has a resistance of 4 Ω and a full scale deflection is produced by 12 mA current. What resistance must be connected in series with it to enable it to read 1.2 V ?

• 45 Ω

• 96 Ω

• 80 Ω

• 40 Ω

An iron rod of volume 10^-4 m³ and relative permeability 1000 is placed inside a long solenoid having 5 turns/cm. If a current of 5.0 A is passed through the solenoid, then magnetic moment of the rod is

• 20 A-m²

• 25 A-m²

• 30 A-m²

• 35 A-m²

In a uniform magnetic field, an $\mathrm{\pi }$-shaped metal frame is located perpendicular to the plane of the conductor and varying with time at the rate (dB /dt)=0.20 T/s. A conducting connector starts moving with an acceleration a = 30 cm/s along the parallel bars of the frame. The length, l of the conductor is equal to 44 cm. If at the moment t = 0, the loop area and magnetic induction are equal to zero, then the emf induced in the loop t = 1s after the beginning of motion is

• 6 × 10^-4 V

• 8 × 10^-2 V

• 6 × 10^-2 V

• 12 × 10^-3 V

A toroid having 200 turns carries a current of 1A. The average radius of the toroid is 10 cm. The magnetic field at any point in the open space inside the toroid is

• 4 × 10^-3 T

• 0.5 × 10^-3 T

• 0

• 3 × 10^-3 T

An electric current passes through a long straight copper wire. At a distance 5 cm from the straight wire, the magnetic field is B. The magnetic field at 20 cm from the straight wire would be

• $\frac{\mathrm{B}}{6}$

• $\frac{\mathrm{B}}{4}$

• $\frac{\mathrm{B}}{3}$

• $\frac{\mathrm{B}}{2}$

In a hydrogen atom, the electron is making 6.6 × 10¹⁵  rps in a circular path of radius 0.53 $\stackrel{\circ }{\mathrm{A}}$. What is the magnetic induction produced at the centre of orbit ?

• 6.3 T

• 12.6 T

• 18.9 T

• 25.2 T

A cell is connected between the points A and C of a circular conductor ABCD with O as centre and angle AOC = 60°. If B₁ and B₂ are the magnitudes of the magnetic fields at O due to the currents in ABC and ADC respectively, then ratio $\frac{{\mathrm{B}}_1}{{\mathrm{B}}_2}$ is 

• 1

• 2

• 5

• 6