A straight wire of mass \(200~\text{g}\) and length \(1.5~\text{m}\) carries a current of \(2~\text{A}\). It is suspended in mid-air by a uniform horizontal magnetic field \(B\) (shown in the figure). What is the magnitude of the magnetic field?

1. \(0.65~\text{T}\)
2. \(0.77~\text{T}\)
3. \(0.44~\text{T}\)
4. \(0.20~\text{T}\)

In a region of space, magnetic field is parallel to the positive y-axis and the charged particle is moving along the positive x-axis (as shown in the figure). The directions of Lorentz force for an electron (negative charge) and proton (positive charge) are respectively:

1. -z-axis, +z-axis

2. +z-axis, -z-axis

3. -z-axis, -z-axis

4. +z-axis, +z-axis

The radius of the path of an electron and frequency (mass $9\times {10}^{-31} \mathrm{kg}$ and charge $1.6\times {10}^{-19} \mathrm{C}$) moving at a speed of \(3\times10^7\) m/s in a magnetic field of \(6\times10^{-4}\) T perpendicular to it are respectively:
1. \(24\) cm, \(4\) MHz
2. \(22\) cm, \(4\) MHz
3. \(28\) cm, \(2\) MHz
4. \(26\) cm, \(2\) MHz

An electron $\left(mass 9\times {10}^{-31} kg and charge 1.6\times {10}^{-19} C\right)$ is moving at a speed of 3 ×10⁷ m/s in a magnetic field perpendicular to it. The energy of the electron in keV is: ( 1 eV = 1.6 × 10^–19 J)

1. 2.5 keV

2. 3.5 keV

3. 20 keV

4. 3.0 keV