Part 2 of 2 Velocity Selector and Mass Spectrometer An ion is sent through a vel

Question

Part 2 of 2 Velocity Selector and Mass Spectrometer An ion is sent through a velocity selector, and then into a mass spectrometer as shown. The orange crosses indicate the magnetic field going into the page Answer the following questions. 5.0 Points Question 4 of 6 The strengths of the electric and magnetic fields inside the velocity selector are respectively E 500 V/m and B1 0.0200 T. What is the speed of the ions that are selected? A 4.00 × 10-5 m/s B. 2.50 × 105 m/s 5.00 × 102 m/s D. 2.50 x 104 m/s E. 10.0 m/s eset Sel

Explanation / Answer

Question 4

The ions pass through a velocity selector. This a region with a uniform electric and magnetic field. The electric field comes from a set of parallel plates. The field is perpendicular to the velocity of the ions and exerts a force of qE on the ions. The magnetic field is perpendicular to both the ion velocity and the electric field. The magnetic force has a magnitude qvB, and is opposite in direction to the electric force. The forces balance when:

qE = qvB

E = vB

v = E/B

Important information to understand the basic concept about velocity selector:

For ions with a larger speed the magnetic force exceeds the electric force and those ions are deflected out of the beam. Ions with a smaller speed are deflected out of the beam in the other direction, because for those ions the electric force is larger than the magnetic force.

now v = E/B = 500 / 0.02 = 25000 m/s

Question 5

All the ions, with the same charge and velocity, enter the mass separation stage, which is simply a region with a uniform magnetic field at right angles to the velocity of the ions. Such a magnetic field causes the charges to follow circular paths of radius r = mv / qB.

B2 = 5 x 10^-3 T radius of trajectory = 0.626 m.

now we get q / m = v / r*B = 25000 / 0.626*(5 x 10^-3) = 7.99 x 10^6 C/kg

Question 6

since the beam of ions entering the mass spectrometer experiences the force in the upward direction, with the magnetic field into the plane we can infer by right hand rule that the beam consists of positive ions.

Option C

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