Design: Variables: Controlled: Manipulated: Responding: Graph/n LAB: MASS SPECTROMETER Background Information: An instrument that makes use of the combination of centripetal motion and magnetic deflection of charged particles is the mass spectrometer. A mass spectrometer is an instrument that separates particles according to their masses. Say, for example, a scientist wants to study the isotopes of lithium. Isotopes, you may recall from chemistry, have the same atomic number (number of protons) but a different atomic mass (number of protons + neutrons). The element is first placed in an ion generation and accelerator chamber where it is ionized (the atoms are stripped of their outer electrons) resulting in Li* ions. The ions are then accelerated through an electric potential and they pass into the spectrometer. Since every ion has the same charge, speed and initial path, any differences in their circular paths are due to differences in mass - the lighter isotopes will travel in smaller circles than heavier isotopes. Step 1: Ion Accelerator Atoms are ionized either by extreme heating or by electrical discharge. The ions are then accelerated through a potential difference (V) where they gain kinetic energy. Ek = E₁Vq= Ee→ 1 Step 2: Velocity selector The beam of electrons is sent through a perpendicular magnetic field and electric field. When the fields are adjusted so that the magnetic and electric forces cancel out, the electrons go straight through undeflected. This allows us to determine the speed of the electrons in the beam. A simulation can show how an electric field will appear around a charged particle. Step 3: Ion Separator E Fm = FE→ quB = Eq→ B Once you know the speed of the electrons, the charged particle is then sent through a magnetic field and we can use the curvature of the charged particle while traveling through the magnetic field to calculate Procedure: mv2 Fm = qvB Fc → = T 1. Go to https://www.geogebra.org/m/tuc284pj 2. Adjust V1 and V2 to a non-zero value, then adjust the magnetic field B2 until the particle travels straight through the velocity selector. Record the values of V1, V2 and B2 on the table below. 3. Adjust the magnetic field in B3 and record the radius in which the particle travels. 4. Calculate the speed in the velocity selector assuming that the distance between the plates is 0.04 m. 5. Repeat step 2-4 until you have 5 data points. Observations: Constants: Distance between plates in stage 2: 0.0400 m Magnetic Field 3: Trial 1 2 3 4 5 Voltage 1 (V) Voltage 2 (V) Magnetic Field 2 (B) Radius (m) Analysis: Calculate the speed of the particles in the velocity selector. Trial Radius (m) Speed (m/s) 1 2 3 4 5 Plot a graph of velocity. as a function of radius.