MAGNETIC EFFECTS OF ELECTRIC CURRENT AND MAGNETISM

6 )

If a long hollow copper pipe carries a direct current, the magnetic field associated with the current will be ______

Only inside the pipe

Only outside the pipe

Neither inside nor outside the pipe

Both inside and outside the pipe

View Solution

Answer :

There will be enclosed current only when the observation point is outside

the pipe.

For inside the pipe I = 0

∴ B = [(μ₀ I) / (2πr)] = 0

hence inside magnetic field = 0.

∴ field will be outside the pipe.

7 )

The magnetic induction at a point P which is at a distance 4 cm from a long current carrying wire is 10^–8 tesla. The field of induction at a distance 12 cm from the same current would be _________ tesla.

3.33 Ã— 10^â€“9

1.11 Ã— 10^â€“4

3 Ã— 10^â€“3

9 Ã— 10^â€“2

View Solution

Answer :

We know that B ∝ (1/r)

∴ (B₁ / B₂) = (r₂ / r₁)

when r₁ = 4 cm, B₁ = 10^–8 T

when r₂ = 12 cm, then B₂ is [(B₁r₁) / r₂]

∴ B₂ = 10^–8 × (4 / 12) = 3.33 × 10^–9 T

8 )

The strength of the magnetic field at a point y near a long straight current carrying wire is B. The field at a distance y/2 will be _________

B/2

B/4

View Solution

Answer :

we know B ∝ (1/r)

As distance y is changed to (y/2) i.e. distance is halved hence by above

relation field will be doubled, hence new field = 2B.

9 )

The mag. field (B) at the centre of a circular coil of radius "a", through which a current I flows is _________

B âˆ a

B âˆ (1/I)

B âˆ I

B âˆ I^2

View Solution

Answer :

For a circular coil, B = (μ₀I / 2a) hence B ∝ I

10 )

A current of a 1 Amp is passed through a straight wire of length 2 meter. The magnetic field at a point in air at a distance of 3 meters from either end of wire and lying on the axis of wire will be _________

(Î¼0 / 2Ï€)

(Î¼0 / 4Ï€)

(Î¼0 / 8Ï€)

zero

View Solution

Answer :

For straight wire,

B = (μ₀ / 4π)(I/d)(sinθ₁ + sinθ₂)

here

θ₁ = θ₂ = 0, as sinθ = sin0 = 0

hence B = 0

Topic Categories