A charged particle with velocity 2 × 10³ m/s passes undeflected through electric and magnetic field. Magnetic field is 1.5 tesla. The electric field intensity would be

2 × 10³N/C
1.5 × 10³N/C
3 × 10³N/C
4/3 × 10^–3N/C

Solution

E = vB = 2 × 10³ × 1.5 = 3 × 10³V/m.

Two long parallel wires P and Q are held perpendicular to the plane of paper with distance of 5 m between them. If P and Q carry current of 2.5 amp. and 5 amp. respectively in the same direction, then the magnetic field at a point half-way between the wires is

μ₀/17
√3μ₀/2π
μ₀/2π
3μ₀/2π

Solution

Two straight long conductors AOB and COD are perpendicular to each other and carry currents I₁ and I₂

\(\frac{\mu _{0}}{2\pi a}(I_{1}+I_{2})\)
\(\frac{\mu _{0}}{2\pi a}(I_{1}-I_{2})\)
\(\frac{\mu _{0}}{2\pi a}(I_{1}^{2}-I_{2}^{2})^{\frac{1}{2}}\)
\(\frac{\mu _{0}}{2\pi a}\frac{I_{1}I_{2}}{I_{1}+I_{2}}\)

Solution

The point P is lying symmetrically w.r.t. the two long straight current carrying conductors. The magnetic fields at P due to these current carrying conductors are mutually perpendicular.

A current of 3 A is flowing in a linear conductor having a length of 40 cm. The conductor is placed in a magnetic field of strength 500 gauss and makes an angle of 30º with the direction of the field.It experiences a force of magnitude

3 × 10^–4 N
3 × 10^–2 N
3 × 10² N
3 × 10⁴N

Solution

F= Il B sin θ= 3 × 0.40 × (500 × 10^-4) × sin 30º= 3 × 10^-2N.

An electron moves in a circular arc of radius 10 m at a contant speed of 2 × 10⁷ ms^-1 with its plane of motion normal to a magnetic flux density of 10^–5 T. What will be the value of specific charge of the electron?

2 × 10⁴C kg^–1
2 × 10⁵C kg^–1
5 × 10⁶C kg^–1
2 × 10¹¹C kg^–1

Solution

Bqv = mv²/r or q/m =v /rB.

An electron moving with kinetic energy 6×10^–16 joules enters a field of magnetic induction 6 × 10^–3 weber/m² at right angle to its motion. The radius of its path is

3.42 cm
4.23 cm
5.17 cm
7.7 cm

Solution

A wire of length L metre carrying a current  ampere is bent in the form of a circle. Its magnitude of magnetic moment will be

IL/4π
I²L²/4π
IL²/4π
IL²/8π

Solution

If r is the radius of the circle,

then L = πr² or, r = ^L²⁄_2π

Area = π² = πL²/4π² = L²/4π

Two concentric circular coils of ten turns each are situated in the same plane. Their radii are 20 and 40 cm and they carry respectively 0.2 and 0.4 ampere current in opposite direction.The magnetic field in weber/m² at the centre is

μ₀/80
7μ₀/80
(5/4)μ₀
zero

Solution

A helium nucleus makes a full rotation in a circle of radius 0.8 meter in 2 sec. The value of the magnetic field induction B in tesla at the centre of circle will be

2 × 10^-19 μ₀
10^-19/μ₀
10^-19 μ₀
2 × 10^-20/μ₀

Solution

A portion of a conductive wire is bent in the form of a semicircle of radius r as shown below in fig. At the centre of semicircle, the magnetic induction will be

zero
infinite
\(\frac{\mu 0}{4\pi }.\frac{\pi i}{r}gauss\)
\(\frac{\mu 0}{4\pi }.\frac{\pi i}{r}tesla\)

Solution

The straight part will not contribute magnetic field at the centre of the semicircle because every element of the straight part will be 0º or 180º with the line joining the

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