An electric current I flows through an infinitely long conductor as shown in Figure below. Write an expression and direction for the magnetic field at point P .

By Biot Savart ' s law B → = ∫ d B → = μ 0 4 π ∫ I dl → × r → r 3 = μ 0 I 4 πr cos θ 1 - cos θ 2 where r is the perpendicular distance of the point from the wire. For an infinitely long conductor, θ 1 = 0 and θ 2 = π ⇒ B → = μ 0 I 4 πr × cos 0 ° - cos 180 ° = μ 0 I 2 πr The magnetic field created by current carrying wire is radial magnetic field.

Calculate force per unit length acting on the wire B due to the current flowing in the wire A. (See figure 2 below):

Given r = 1 c m , I 1 = 20 A , I 2 = 75 A Here by using the relation F l = μ 0 2 π I 1 I 2 r = 2 × 10 - 7 × 20 × 75 10 - 2 F = 3 × 10 - 2 N towards A . (attracting force)

A long horizontal wire P carries a current of 50 A . It is rigidly fixed. Another wire Q is placed directly above and parallel to P as shown in Figure 1 below. The weight per unit length of the wire Q is 0 . 025 N m - 1 and it carries a current of 25 A . Find the distance r of the wire Q from the wire P so that the wire Q remains at rest.

Given I 1 = 50 A , W / L = 0 . 025 N m - 1 , I 2 = 25 A The Force between the wires will balance the weight of the wire Q. F L = μ 0 I 1 I 2 2 π r On putting values we get r = 10 - 2 m

A moving charged particle q travelling along the positive X-axis enters a uniform magnetic field B . When will the force acting on q be maximum?

The force experienced by the charge is given by F = B q v sin θ . where θ is the angle between the velocity vector and the magnetic field. F = F max when v → ⊥ B → . So, for maximum for B → must be along Y-axis or Z-axis.

E M B I B E

EMBIBE CHAPTER WISE PREVIOUS YEAR PAPERS FOR PHYSICS>Chapter 7 - Moving Charges and Magnetic Field>ICSE-2019>Q 6

EASY

12th ICSE

IMPORTANT

Earn 100

An electric current I flows through a circular loop as shown in Figure below. Write an expression and direction for the magnetic field at the centre of the loop at point $P$ .

Important Questions on Moving Charges and Magnetic Field

MEDIUM

12th ICSE

IMPORTANT

EMBIBE CHAPTER WISE PREVIOUS YEAR PAPERS FOR PHYSICS>Chapter 7 - Moving Charges and Magnetic Field>ICSE-2020>Q 7

Write Biot-Savart's law in vector form.

MEDIUM

12th ICSE

IMPORTANT

EMBIBE CHAPTER WISE PREVIOUS YEAR PAPERS FOR PHYSICS>Chapter 7 - Moving Charges and Magnetic Field>ICSE-2020>Q 8

Write an expression for force per unit length between two long current-carrying wires, kept parallel to each other, in a vacuum and hence define an ampere, the SI unit of current.