The next two problems refer to the figure on the right. Neglect gravity, and neg

Question

The next two problems refer to the figure on the right. Neglect gravity, and neglect friction in all questions! Electrons are sent in with an initial velocity to the right through a region where there is a uniform electric field, E (shown) and a uniform magnetic field B (not shown). If you want these electrons to travel straight through (unelected), which direction should the magnetic field, B, point? Up the page (opposite the E field). Down the page (i.e. the same way the E field points). To the right (i.e. the same way the electrons travel). Out of the page Into the page. If the strength of the uniform vertical E field in the previous problem is 3000 V/m, and the strength of the magnetic field is 600 T, how fast must the electrons be going for straight line travel?

Explanation / Answer

Answer: D) magnetic field should be directed out of page.

To go straight, net force on electronshould be zero i.e FB-+E =0

=>FB=-FE i.e forces should be equal in magnitude opposite in direction

Electric force on electron(-ve charged particle) is in opposite direction to Electric field direction

=> FE is up the page

Therefore, FB should be down the page

From right hand rule, magnetic field should be directed out of page.

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