A charged particle moving with a uniform velocity v → , enters a region where uniform electric and magnetic fields E → and B → are present. It passes through the region without any change in velocity. What can we conclude about the ( a ) Relative directions of E → , v → and B → . b Magnitudes of E → and B → .

a Let E → be the strength of electric field and B → be the strength of magnetic field. If F m → and F e → are the electric and magnetic forces acting on the charged particle then, net force F n e t → on that charged particle is given by, From Lorentz force, F n e t → = F e → + F m → F n e t → = q ( E → + v → × B → ) Since, the particle is moving without any change in its velocity, acceleration in the particle, a → = F n e t → m = 0 ⇒ F n e t → = 0 The forces on charged particle due to electric field and magnetic field are equal and opposite. ⇒ 0 = q ( E → + v → × B → ) ⇒ E → = - v → × B → ∴ E → ⊥ v → , E → ⊥ B → and v → is not parallel or anti-parallel to B → . If the charged particle is moving perpendicular to the direction of B → , it experiences a maximum force which acts perpendicular to the direction of B → as well as v → and that force is balanced by electric force which is acting opposite to the direction of B → as well as v → and hence the charged particle moves without any change in velocity. Therefore, All three E → , v → and B → are mutually perpendicular to each other. b The force on charged particle q due to perpendicular magnetic field, F m = q v B sin θ where θ is the angle between the velocity vector and magnetic field. F m = q v B sin 90 ° = q v B Force on charged particle due to perpendicular electric field, F e = q E As the charged particle goes undeflected, so q v B = q E or v = E B

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A loop of irregular shape, carrying current is placed in an external magnetic field. What shall happen if the wire is flexible?

Important Questions on Electromagnetism

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IMPORTANT

A Text Book of PHYSICS PART 2 : CLASS 12>Chapter 8 - Electromagnetism>EXERCISE 8>Q 51

An electron beam projected along X-axis experience a force due to a magnetic field along Y-axis. What is the direction of magnetic field?

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A Text Book of PHYSICS PART 2 : CLASS 12>Chapter 8 - Electromagnetism>EXERCISE 8>Q 52

Two identical charged particles moving with same speed enter a region of uniform magnetic field. If one of these enters normal to the field direction and the other enters along a direction at

30 °

with the field, what would be the ratio of their angular frequencies?

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A Text Book of PHYSICS PART 2 : CLASS 12>Chapter 8 - Electromagnetism>EXERCISE 8>Q 53

State the rule with the help of which we can determine the polarity of an electromagnet?

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A Text Book of PHYSICS PART 2 : CLASS 12>Chapter 8 - Electromagnetism>EXERCISE 8>Q 54

State any rule which relates the direction of electric current and direction of accompanying magnetic field.

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A Text Book of PHYSICS PART 2 : CLASS 12>Chapter 8 - Electromagnetism>EXERCISE 8>Q 55

A charged particle moving with a uniform velocity

\vec{v}

, enters a region where uniform electric and magnetic fields

\vec{E}

and

\vec{B}

are present. It passes through the region without any change in velocity. What can we conclude about the

(a)

Relative directions of

\vec{E}

\vec{v}

and

\vec{B}

(b)

Magnitudes of

\vec{E}

and

\vec{B}

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A Text Book of PHYSICS PART 2 : CLASS 12>Chapter 8 - Electromagnetism>EXERCISE 8>Q 56

A beam of protons projected along

+ X

-axis experiences a force, due to a magnetic field, along the

Y

-axis. What is the direction of the magnetic field?

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A Text Book of PHYSICS PART 2 : CLASS 12>Chapter 8 - Electromagnetism>EXERCISE 8>Q 57

A proton and an alpha particle having the same kinetic energy are allowed to pass through a uniform magnetic field perpendicular to their direction of motion. Compare the radii of the paths of proton and alpha particle.

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A Text Book of PHYSICS PART 2 : CLASS 12>Chapter 8 - Electromagnetism>EXERCISE 8>Q 58

A proton and an alpha particle enters a uniform magnetic field perpendicular with the same speed. How many times is the time-period of the

α

-particle more than that of the proton? Deduce an expression for the ratio of the radii of circular paths of the two particles.

A loop of irregular shape, carrying current is placed in an external magnetic field. What shall happen if the wire is flexible?

Important Questions on Electromagnetism

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