As initially discussed in the introductory lesson on magnetism, moving charges when exposed to magnetic forces are constrained to move in circular paths. The formula that allows you to calculate the radius of these circular paths is:
where FC represents the centripetal force which is being supplied by FB, the magnetic force. Solving for r yields
Right Hand Rule
The right hand rule, RHR, for determining the direction of the force experienced by a moving positive charge in a magnetic field is:
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thumb points in the direction of a moving positive charge's velocity, v
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fingers point in the direction of magnetic field, B
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palm faces in the direction of the magnetic force, F
In the following diagram, the use of the RHR can help us distinguish between the tracks for positive charges and the tracks for negative charges.
Reflecting on the top circle, if our right thumb (v) points to the left (+x), our fingers (B) into the plane of the page (-z), then our palm (F) would point down (-y). Our palm points to the center of the circle which confirms that the particle is positively charged.
Reflecting on the bottom circle, if our right thumb (v) points to the left (+x), our fingers (B) into the plane of the page (-z), then our palm (F) would point down (-y). Our palm NO LONGER points to the center of the circle which confirms that the particle is NOT positively charged. This path must therefore be one of a negatively charged particle. This can be confirmed by using the LHR in which your palm will once again point to the center of the circle.
Natural Radioactivity Magnetic fields can be used to distinguish emissions from naturally radioactive elements. The three natural modes of radioactive decay are: alpha (α), beta (β), gamma (γ).
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Alpha particles are helium nuclei (particles containing two protons and two neutrons) and are positively charged (+2e).
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Beta particles are electrons released from the nucleus when neutrons decay according to the reaction n → p+ + β- + anti-electron neutrino. These particles have the same charge and mass as "normal" electrons.
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Gamma radiation is electromagnetic energy that is released when a nucleus goes through "de-excitation". Gamma radiation has no charge.
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