When a cathode ray is deflected by a magnetic field, what can you conclude about the nature of the particles in the ray?

• A. The particles in the cathode ray have no mass.
• B. The particles in the cathode ray are electrically neutral.
• C. The particles in the cathode ray are photons.
• D. The particles in the cathode ray possess electric charge.

Answer: (D)

Verified step by step guidance

1. Recall that a magnetic field exerts a force on moving charged particles according to the Lorentz force law, which is given by \(\mathbf{F} = q(\mathbf{v} \times \mathbf{B})\), where \(q\) is the charge, \(\mathbf{v}\) is the velocity, and \(\mathbf{B}\) is the magnetic field.
2. Understand that if the particles in the cathode ray were electrically neutral (i.e., \(q=0\)), then the magnetic force \(\mathbf{F}\) would be zero, and the particles would not be deflected by the magnetic field.
3. Since the cathode ray is observed to be deflected by the magnetic field, it implies that the particles must carry an electric charge, because only charged particles experience a magnetic force that can change their trajectory.
4. Note that the deflection also indicates the particles have mass, as massless particles like photons would not behave in this way under a magnetic field; photons are neutral and unaffected by magnetic fields.
5. Therefore, the conclusion is that the particles in the cathode ray possess electric charge, which is why they are deflected when passing through a magnetic field.