Question

Cathode rays are moving along the positive $Z$-axis.An electric field is applied along positive $Y$-axis. In the same region, a magnetic field is also applied.The cathode rays pass undeviated in this region.What is the direction of the magnetic field?

• A. Positive $x$-axis
• B. Negative $x$-axis
• C. Negative $y$-axis
• D. Positive $z$-axis

Answer 1

Answer: (B)

Negative $x$-axis

The electric force on cathode rays is in $+Y$ direction. In order to balance it, magnetic force should act in $-Y$ direction. Magnetic field should be in -$X$ axis.