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Figure 1 shows a gas discharge tube devised by William Crookes in one of his investigations - AQA - A-Level Physics - Question 1 - 2017 - Paper 7
Question 1
Figure 1 shows a gas discharge tube devised by William Crookes in one of his investigations. When a large potential difference is applied between the cathode and an... show full transcript
Worked Solution & Example Answer:Figure 1 shows a gas discharge tube devised by William Crookes in one of his investigations - AQA - A-Level Physics - Question 1 - 2017 - Paper 7
Step 1
Explain how this experiment led Crookes to conclude that cathode rays are particles and these particles caused the movement of the paddle.
Answer
In the gas discharge tube, when a high potential difference is applied, cathode rays (which are particles) emanate from the cathode toward the anode. This movement causes the paddle wheel to gain kinetic energy, demonstrating that the rays are indeed particles as they exert a force on the paddle. The observed motion of the paddle wheel confirms that the cathode rays move in a straight line and possess momentum, illustrating their nature as particles.
Step 2
Explain how cathode rays are produced in a gas discharge tube.
Answer
Cathode rays are generated when a high voltage is applied across the electrodes in the discharge tube. This voltage causes electrons to be pulled out of the cathode and escape into the tube. As they travel towards the anode, they collide with gas atoms, which ionizes the atoms and results in the emission of more electrons, thus allowing a continuous flow of cathode rays across the tube.
Step 3
Suggest the effect that this absorption may have on the motion of the paddle wheel. Give a reason for your answer.
Answer
The absorption of air molecules by the walls of the tube may lead to a decrease in the number of particles available for collision with the cathode rays. This results in fewer collisions that would otherwise transfer momentum to the paddle wheel. Consequently, the effect would likely be that the paddle wheel rotates less or moves slower because of reduced force exerted by the particles.