An electron moving to the right with a speed v enters a region of applied electr

Question

An electron moving to the right with a speed v enters a region of applied electric and magnetic fields. The electric field with a magnitude of 5.7 x 10^3 N/C is pointing downward. The magnitude of the magnetic field is 4.3 x10^-4 T. The electron’s velocity is unchanged as it travels through the fields.

What is the direction of the applied magnetic field?

A) up

B) down

C) into the page

D) out of the page

E) None of the above.

What is the speed of the electron, v?

A) 7.5 x 10^-8 m/s

B) 2.5 m/s

C) 6.6 x 10^6 m/s

D) 1.3 x 10^7 m/s

E) Not enough information if given.

Explanation / Answer

the electric field E=5.7*10^3 N/c

the magnetic field B=4.3*10^-4T

this concept belongs to electro agnetic induction

according to the concept of the motional emf

(a) ans

the direction of the magnetic field is into the page basing on motional emf

so the option C is correct

(b) ans

the velocity v=E/B=5.7*10^3/4.3*10^-4=1.3*10^7 m/s

so the correct option is D

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