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Figure 1 shows a diagram of a discharge tube used by JJ Thomson to investigate cathode rays - AQA - A-Level Physics - Question 1 - 2020 - Paper 7
Question 1
Figure 1 shows a diagram of a discharge tube used by JJ Thomson to investigate cathode rays. The direction XY is horizontal and at right angles to the axis of the t... show full transcript
Worked Solution & Example Answer:Figure 1 shows a diagram of a discharge tube used by JJ Thomson to investigate cathode rays - AQA - A-Level Physics - Question 1 - 2020 - Paper 7
Step 1
Describe how a cathode ray is produced in the discharge tube in Figure 1.
Answer
A cathode ray is produced when a high-voltage power supply is connected to the discharge tube. This potential difference causes electrons to be emitted from the cathode, usually a heated metal element. These electrons are then accelerated towards the anode due to the electric field created by the high-voltage supply, resulting in a focused stream of cathode rays that travel in a straight line and eventually strike the fluorescent screen, causing it to emit light.
Step 2
Step 3
Explain how the cathode ray is restored to its original path by adjusting only the electric field strength between P and Q.
Answer
By increasing the electric field strength between plates P and Q, the force acting on the cathode rays is increased, allowing for a corresponding adjustment to counteract any deflection caused by their increased speed. This ensures the particles follow the original path.
Step 4
Explain how the cathode ray is restored to its original path by adjusting only the magnetic flux density.
Answer
Adjusting the magnetic flux density involves increasing it to create a stronger magnetic force acting on the moving cathode rays. This increased force compensates for the higher velocity of the rays, allowing them to maintain their original straight-line path.
Step 5
Discuss the significance of Thomson’s results for the particles in cathode rays, when compared with the specific charge of the hydrogen ion.
Answer
Thomson's results were significant because they demonstrated that the specific charge (charge-to-mass ratio) of the particles in cathode rays was much greater than that of hydrogen ions. This indicated that electrons had a much lower mass compared to protons, implying that they were fundamental constituents of atoms. Thus, the experimental results helped establish the nature of cathode rays and contributed to the understanding of atomic structure.