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Moving Charges And Magnetism

Question

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Answer the following questions:
An electron travelling west to east enters a chamber having a uniform electrostatic field in north to south direction. Specify the direction in which a uniform magnetic field should be set up to prevent the electron from deflecting from its straight line path.

Solution

The electrostatic field is directed towards south. Since the electron is a negatively charged particle, therefore, the electrostatic field shall exert a force directed towards north.
So, if the electron is to be prevented from deflection from straight path, the magnetic force on the electron should be directed towards south.
Magnetic force is given by,

\vec{F} = - e (\vec{v} \times \vec{B}) .

{\vec{F}}_{m}

is towards south,

\vec{v}

is travelling towards east.

Applying Fleming's Left-Hand Rule, we find that magnetic field

\vec{B}

should be in the vertically downward direction.

Some More Questions From Moving Charges And Magnetism Chapter

Two moving coil meters, M₁ and M₂ have the following particulars:
R₁ = 10 Ω N₁ = 30,
A₁ = 3.6 x 10^–3 m², B₁ = 0.25 T
R₂ = 14 Ω; N₂ = 42,
A₂ = 1.8 x 10^–3 m², B₂ = 0.50 T
(The spring constants k are identical for the two meters).
Determine the ratio of (a) current sensitivity and (b) voltage sensitivity of M₂ and M_1.

Answer the following questions:
A charged particle enters an environment of a strong and non-uniform magnetic field varying from point to point both in magnitude and direction, and comes out of it following a complicated trajectory. Would its final speed equal the initial speed if it suffered no collisions with the environment?

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