The turns of a solenoid, designed to provide a given magnetic flux density along its axis, are wound to fill the space between two concentric cylinders of fixed radii. How should the diameter d of the wire used be chosen so as to minimize the heat dissipated in the windings?

• Wire should be multiple of 5d

• Wire should be multiple of d/3

• the wire is independent of d

• Can't say

A long straight wire is carrying current I in the +z direction. The x-y plane contains a closed circular loop carrying current I₂ and not encircling the straight wire. The force on the loop will be

• $\frac{{\mathrm{\mu }}_0{\mathrm{I}}_1{\mathrm{I}}_0}{2\mathrm{\pi }}$

• $\frac{{\mathrm{\mu }}_0{\mathrm{I}}_1{\mathrm{I}}_0}{4\mathrm{\pi }}$

• zero

• Depends on the distance of the centre of the loop from the wire.

To reduce the range of voltmeter, its resistance needs to be reduced. A voltmeter has resistance Ro and ranges V. Which of the following resistances when connected in parallel will convert it into a voltmeter of range V/n?

• nR₀

• (n+1)R₀

• (n-1)R

• None of these

A charged particle is suspended equillibrium in a uniform vertical electric field of intensity 2000V/m. If mass of the particle is 9.6×10^-16 kg, the charge on it and excess number of electrons on the particle respectively are (g=10m/s²)

• 4.8×10^-19 C,3

• 5.8×10^-19 C,4

• 3.8×10^-19C, 2

• 2.8×10^-19 C, 1

A proton enters a magnetic field of intensity 1.5 Wb/m² with a velocity 2×10⁷ m/s in a direction at angle 30^o with the field. The force on the proton will be (charge on proton is 1.6×10^-19 C)

• 2.4×10^-12 N

• 4.8×10^-12 N

• 1.2×10^-12 N

• 7.2×10^-12 N

20 ampere current is flowing in a long straight wire. The intensity of magnetic field at a distance 10 cm from the wire will be

• 2×10^-5 Wb/m²

• 9×10^-5 Wb/m²

• 4×10^-5 Wb/m²

• 6×10^-5 Wb/m²

37.

The resistance of a galvanometer is 50 Ω. When 0.01A current flows in it, full scale deflection is obtained in galvanometer, the resistance of shunt connected to convert galvanometer into an ammeter of range 5A, will be

• 0.1 Ω

• 0.2 Ω

• 0.3 Ω

• 0.4 Ω

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

• $\frac{{\mathrm{\mu }}_0{\mathrm{NiR}}^2}{2{\left({\mathrm{R}}^2+{\mathrm{x}}^2\right)}^{{\displaystyle \raisebox{1ex}{$3$}\!\left/ \!\raisebox{-1ex}{$2$}\right.}}}$

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

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

• Zero

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

• 2.9 cm

• 3.9 cm

• 2.35 cm

• 2 cm

If a charge particle enters perpendicularly in the uniform magnetic field, then:

• energy and momentum both remains constant

• energy remains constant but momentum changes

• both energy and momentum changes

• energy changes but momentum remains constant