It is desired to construct a velocity selector for Kr-84 ions that will pick out

Question

It is desired to construct a velocity selector for Kr-84 ions that will pick out ions of speed 4 3 10 × m/s, as needed in problem 1. Suppose the ions move horizontally from left to right so that their velocity is ( ) 4 3 10 m/s × i. When they enter the velocity selector they encounter an electric field E = ?( 3000V/m) ? j (see the sketch below).

(a) Calculate the magnitude and direction of the magnetic field in the velocity selector if the ions are to go straight through in the i direction without deflection.

(b) Suppose it is desired to use the above velocity selector to pick out Kr-86 ions of the same speed (these ions have the same charge as the Kr-84 but a slightly larger mass). How will the strength of the magnetic field have to be changed?

(c) If the Kr-84 ions were doubly ionized (i.e. had a charge of +2e), how would the magnetic field in part (a) have to be changed?

Explanation / Answer

we know the relation between electric field and megnetic field

E = v x B

a)

3000 (-j) = 30000 i x B

B = 0.1 k T

b) here we know megnetic field (B) is depend on speed of particle. so strength of the megnetic field will not be changed.

c) also B does not depend on charge so B will not be changed.

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