Moving Charges and Magnetism

Moving Charges and Magnetism

Moderate Questions
Difficult Questions

Electricity and Magnetism

Current Electricity
Moving Charges and Magnetism
Magnetism and Matter
Electromagnetic Induction
Alternating Current
Electromagnetic Waves
  1. Tesla is the unit of








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    ​Tesla is the unit of magnetic field.

    Correct Option: B

    ​Tesla is the unit of magnetic field.

  1. ​If a long hollow copper pipe carries a current, then magnetic field is produced​








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    ​Inside a hollow pipe carrying current, the magnetic field is zero, since according to Ampere’s law, Bi. 2πr = µ0 × 0 ⇒ Bi = 0.
    ​But for external points, the current behaves as if it was concentrated at the axis only; so, outside,

    B1 =
    μ0i
    2πr

    . Thus, the magnetic field is produced outside the pipe only.

    Correct Option: B

    ​Inside a hollow pipe carrying current, the magnetic field is zero, since according to Ampere’s law, Bi. 2πr = µ0 × 0 ⇒ Bi = 0.
    ​But for external points, the current behaves as if it was concentrated at the axis only; so, outside,

    B1 =
    μ0i
    2πr

    . Thus, the magnetic field is produced outside the pipe only.

  1. A coil of one turn is made of a wire of certain length and then from the same length a coil of two turns is made. If the same current is passed in both the cases, then the ratio of the magnetic inductions at their centres will be








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    Let ℓ be length of wire.

    ​Ist case : ℓ = 2πr ⇒ r =
    ℓ
    2πr

    B =
    μ0In
    		 =
    μ0I × 2π
    		 =
    μ0Iπ
    		[∵ n = 1]......(1)
    2r2ℓℓ

    ​2nd Case : ℓ = 2(2πr') ⇒ r' =
    ℓ
    4π

    B' =
    μ0In
    		 =
    2μ0Iπ
    		 = 4
    4μ0Iπ
    		 = 4B , using (1)(where n = 2)
    2
    ℓ
    ℓ
    		ℓ
    4π2

    Correct Option: B

    Let ℓ be length of wire.

    ​Ist case : ℓ = 2πr ⇒ r =
    ℓ
    2πr

    B =
    μ0In
    		 =
    μ0I × 2π
    		 =
    μ0Iπ
    		[∵ n = 1]......(1)
    2r2ℓℓ

    ​2nd Case : ℓ = 2(2πr') ⇒ r' =
    ℓ
    4π

    B' =
    μ0In
    		 =
    2μ0Iπ
    		 = 4
    4μ0Iπ
    		 = 4B , using (1)(where n = 2)
    2
    ℓ
    ℓ
    		ℓ
    4π2

  1. The magnetic field (d→B) due to a small element (dl) at  a distance (→r) and element carrying current i is








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    According to Biot Savart law, ​

    d→B =
    μ0In
    i(d→ℓ × →r)
    4πr³

    Correct Option: D

    According to Biot Savart law, ​

    d→B =
    μ0In
    i(d→ℓ × →r)
    4πr³

  1. Two equal electric currents are flowing perpendicular to each other as shown in the figure. AB and CD are perpendicular to each other and symmetrically placed with respect to the current flow. Where do we expect the resultant magnetic field to be zero?​​








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    Net magnetic field on AB is zero because magnetic field due to both current carrying wires is equal in magnitude but opposite in direction.

    Correct Option: A


    Net magnetic field on AB is zero because magnetic field due to both current carrying wires is equal in magnitude but opposite in direction.