Obtain an expression for the magnetic flux density B ⇀ at the centre of a circular coil of radius R having N turns when a current I flows through it.

* Magnetic field due to circular coil carrying current : consider a small current element of dl on a ring. Let R be the distance from this dl to centre O of the ring then According to Biot-Savart law, dB = μ 0 4 π I dl sin θ R 2 Here θ = Angle between dl → & R → = 90 ° ⇒ dB = μ 0 4 π I dl R 2 Now magnetic field at the centre of circular coil carrying current = B = ∫ 0 2 π R μ 0 Idl 4 π R 2 = μ 0 I 4 π r 2 ∫ 0 2 π R dl= μ 0 I 4 π R 2 × 2 π R ⇒ B= μ 0 I 2 R For N turns in the coil magnetic field is expressed as B= μ 0 NI 2 R

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NOOTAN ISC PHYSICS Class 12 Part-1>Chapter 7 - Moving Charges and Magnetic Field>QUESTIONS>Q 32

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In the given figure, a long, straight current-carrying wire AB is fixed, while the rectangular current-loop is free to move. In which direction would the loop move? Explain with
reason.

Important Questions on Moving Charges and Magnetic Field

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NOOTAN ISC PHYSICS Class 12 Part-1>Chapter 7 - Moving Charges and Magnetic Field>QUESTIONS>Q 33

A body is suspended from the lower end of a vertical spring. What shall be the effect on the position of the body when a current is sent through the spring? Does it depend upon the direction of current in the spring?

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NOOTAN ISC PHYSICS Class 12 Part-1>Chapter 7 - Moving Charges and Magnetic Field>QUESTIONS>Q 34

If the current flowing in the spring be alternating, then?

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NOOTAN ISC PHYSICS Class 12 Part-1>Chapter 7 - Moving Charges and Magnetic Field>QUESTIONS>Q 35

An electron-beam moving with uniform velocity is gradually diverging. When it is accelerated to a very high velocity, it starts converging. Why?

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NOOTAN ISC PHYSICS Class 12 Part-1>Chapter 7 - Moving Charges and Magnetic Field>QUESTIONS>Q 1

State Biot-Savart’s law for the magnetic field due to a current-carrying element, explaining the symbols. Define ‘tesla’ on the basis of this law. How is gauss related to tesla?

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NOOTAN ISC PHYSICS Class 12 Part-1>Chapter 7 - Moving Charges and Magnetic Field>QUESTIONS>Q 2

Discuss analogies and differences between Coulomb’s law and Biot-Savart’s law.

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NOOTAN ISC PHYSICS Class 12 Part-1>Chapter 7 - Moving Charges and Magnetic Field>QUESTIONS>Q 3

A current is flowing through a thin, straight metallic conductor of infinite length. Find expression for the magnetic field at a distance from it.

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NOOTAN ISC PHYSICS Class 12 Part-1>Chapter 7 - Moving Charges and Magnetic Field>QUESTIONS>Q 4

Write an expression for Biot-Savart’s law in vector form. Derive an expression for magnetic field at the centre of a circular current-carrying coil of radius r, with N turns.

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NOOTAN ISC PHYSICS Class 12 Part-1>Chapter 7 - Moving Charges and Magnetic Field>QUESTIONS>Q 5

Obtain an expression for the magnetic flux density