Moving Charges And Magnetism

A coil having N turns carries a current as shown in the figure. The magnetic field intensity at point P is :

• $\frac{{\mathrm{\mu }}_0{\mathrm{NiR}}^2}{2({\mathrm{R}}^2 + {\mathrm{x}}^2{)}^{3/2}}$

• $\frac{{\mathrm{\mu }}_0\mathrm{Ni}}{2\mathrm{R}}$

• $\frac{{\mathrm{\mu }}_0{\mathrm{NiR}}^2}{(\mathrm{R} + \mathrm{x}{)}^2}$

• zero

An electron moves at a right angle to a magnetic field of 1.5 x 10^-2 tesla with a speed of 6 x 10⁷ m/s. If the specific charge of the electron is 1.7 x 10¹¹ coulomb/kg, the radius of the circular path will be

• 2.9 cm

• 3.9 cm

• 2.35 cm

• 2 cm

A charged particle is moving in a uniform magnetic field in a circular path of radius R. When energy of the particle is doubled, then the new radius will be:

• R

• R$\sqrt{2}$

• R/$\sqrt{2}$

•  2R

Magnetic and electric field are acting on a proton moving with velocity $\mathrm{\nu }$. Proton will be undeflected if 

• E is parallel to v, but perpendicular to B

• E and B both are parallel to v

• E and B are perpendicular to each other

• E, B and v are perpendicular to one another and v=$\frac{\mathrm{E}}{\mathrm{B}}$

A current of 0.1 ampere is flowing through a coil of 1000 turns and radius 0.1 metre. The magnetic field at the centre of the coil is

• 2 × 10⁻¹ T

• 4.31 × 10⁻²  T

• 6.28 × 10⁻⁴  T

• 9.81 × 10⁻⁴  T

In a galvanometer of 5 ohm resistance, a wire of 2 ohm resistance is used as a shunt. If the total current is 1 ampere, the fraction of current that will flow through the shunt is

• 1.2 A

• 0.7 A

• 0.5 A

• 0.3 A

A solenoid of length 5O cm and a radius of cross-section 1 cm has 1000 turns of wire wound over it. If the current carried is 5 A, the magnetic field on its axis, near the centre of the solenoid is approximately (permeability of free space ${\mathrm{\mu }}_0$= $4\mathrm{\pi } \times {10}^{-7}$ T-m/A)

• 0.63 × 10⁻² T

• 1.26 × 10⁻² T

• 2.51 × 10⁻² T

• 6.3 T

A magnetic field of 2x10⁻² T acts at right angles to a coil of area 100 cm² with 5O turns. The average emf induced in the coil is 0.1 V. When it is removed from the field in time t,  the value of t is

• 0.1 s

• 0.01 s

• 1 s

• 10 s

A pan containing a layer of uniform thickness of ice is placed on a circular turntable with its centre coinciding with the centre of the turntable. The turntable is now rotated at a constant angular velocity about a vertical axis passing through its centre and the driving torque is withdrawn. There is no friction between the table and the pivot. The pan rotates with the table. As the ice melts

• the angular velocity of the system decreases

• the angular velocity of the system increases

• the angular velocity of the system remains unchanged

• the moment of inertia of the system decreases

The thermo-emf of a themocouple is 25µV /°C at room temperature. A galvanometer of 40Ω resistance, capable of detecting current as low as 10^-5 A, is connected with the thermocouple. The smallest temperature difference that can be detected by this system is

• 16°C

• 12°C

• 8°C

• 20°C