An electron is projected with uniform velocity along the axis of a current-carrying long solenoid. Which of the following is true?

$A$ strong magnetic field is applied on a stationary electron. Then,the electron

$A$ charged particle, when entering a uniform magnetic field, moves in a helical path. If its angular velocity is $4 \pi \times 10^6 \text{ rad s}^{-1}$ and its velocity in the direction of the magnetic field is $3 \times 10^5 \text{ m s}^{-1}$, then the pitch of the helix is: (in $\text{ cm}$)

An electron is allowed to move with constant velocity along the axis of a current-carrying straight solenoid. Which of the following statements are correct?
$A.$ The electron will experience magnetic force along the axis of the solenoid.
$B.$ The electron will not experience magnetic force.
$C.$ The electron will continue to move along the axis of the solenoid.
$D.$ The electron will be accelerated along the axis of the solenoid.
$E.$ The electron will follow a parabolic path inside the solenoid.
Choose the correct answer from the options given below:

An electron is projected along the axis of a circular conductor carrying some current. The electron will experience a force:

$A$ deuteron and a proton moving with equal kinetic energy enter into a uniform magnetic field at a right angle to the field. If $r_{d}$ and $r_{p}$ are the radii of their circular paths respectively,then the ratio $\frac{r_{d}}{r_{p}}$ will be $\sqrt{x} : 1$ where $x$ is ..........