(cathode), anode, target metal and high voltage supply

The idea

In an X-ray tube, the cathode is the negative electrode that includes the heater filament and releases electrons by thermionic emission. The anode is the positive electrode that attracts and accelerates those electrons. The target metal is set into the anode and is where the accelerated electrons are stopped, producing X-rays by two processes: characteristic X-rays from electron transitions and continuous X-rays from deceleration. The high voltage supply maintains a large potential difference between cathode and anode, giving the electrons their kinetic energy.

What earns the marks

• The cathode is the negative electrode and is the source of electrons.
• The anode is the positive electrode that attracts and accelerates the electrons.
• The target metal is the part of the anode where X-rays are produced.
• The high voltage supply maintains the potential difference between cathode and anode.
• Electrons gain kinetic energy from the accelerating voltage before hitting the target.
• X-rays are produced when the electrons interact with the target metal.

Common mistakes and how to put them right

• Thinking the anode releases electrons.

  Put it right: The cathode releases electrons, while the anode attracts them.

• Believing the target metal is the cathode.

  Put it right: The target is part of the anode.

• Confusing the roles of the high voltage supply and the heater.

  Put it right: The high voltage accelerates electrons, while the heater releases them.

• Assuming X-rays are produced at the cathode.

  Put it right: They are produced when electrons strike the target at the anode.

Exam tips

• Match each named component to one clear function before choosing an option.
• Remember that the cathode is negative and the anode is positive.
• Link the high voltage supply to the kinetic energy gained by the electrons.
• Distinguish the target metal from the rest of the anode when the question is specific.