Answer:
Step-by-step explanation:
Yes, to select positrons with the same speed as the electrons, the settings for the electric and magnetic fields on the velocity selector need to be changed.
The velocity selector works by applying both an electric field and a magnetic field perpendicular to each other, as shown in the diagram below:
| B
| /--------->
| / /
| / /
| / /
V | / /
<----------|__/___/_____________
| E
The electrons or positrons enter from the left with an initial velocity, V. The electric field E and magnetic field B are adjusted such that only particles with a specific velocity will be able to pass through the velocity selector and reach the detector on the right.
To select positrons with the same speed as the electrons, the direction of the electric field needs to be reversed. This is because the electric force on a positively charged particle is in the opposite direction of the force on a negatively charged particle. Therefore, if the electric field is reversed, the force on the positron will be in the same direction as the force on the electron. This will allow the positrons with the same speed as the electrons to pass through the velocity selector.
The magnetic field does not need to be changed, as it only affects the trajectory of the particles and not their speed. Therefore, the magnetic field will remain the same as it was for the electrons.
In summary, to choose positrons with the same speed as electrons using the velocity selector, only the direction of the electric field needs to be reversed, while the magnetic field remains the same.