Tutorial 9.4.1.2 Cathode Rays Year 12 Physics - Module 9.3 Motors and Generators For use with Lesson 9.4.1 Cathode Rays 1. Identify the properties of cathode rays that indicated that they might be particles. Justify each property as characteristic of a particle..... 2. Identify the properties of cathode rays that indicated they might have been electromagnetic waves. Justify each property as characteristic of a wave....... 3. Identify the properties of cathode rays that did not support them being either waves or particles. 4. For almost thirty years prominent physicists debated the nature of cathode rays. Explain why the apparent inconsistent behaviour of cathode rays caused debate as to whether they were charged particles or electromagnetic waves. What was the major sticking point in the debate? 5. Describe the experiment that proved the existence of cathode rays as a stream of negatively charged particles.
6. Complete the following table regarding the experiments done to examine the behaviour of cathode rays. Description of Experiment Observations Made Inference or Deductions Made Theory Supported Maltese cross in cathode ray tube Paddle wheel in cathode ray tube Effect of magnetic field on cathode ray Effect of electric field on cathode ray 7. The diagram below shows the pattern produced in a discharge tube at a pressure of 0.1 mm Hg. Label the following: Crookes dark space, Faraday s dark space, anode, cathode, positive electrode, negative electrode, negative glow region and the positive column. The striated positive column has a colour that can vary. The negative glow near the cathode is always blue. Explain............. - 2 -
8. Which of the following properties of cathode rays is incorrect? Cathode rays: (a) come from the cathode of a discharge tube. (b) have a q/m ratio less than that of the hydrogen ion. (c) cause glass to fluoresce. (d) carry energy and momentum. 9. The diagram shows the side view of a simple cathode ray tube. What is the function of the component labelled R? (a) To produce cathode rays (b) To stop cathode rays striking the screen. (c) To deflect the cathode rays vertically. (d) To deflect the cathode rays horizontally. 10. In a first- hand investigation that you performed, you used a discharge tube containing a Maltese Cross. You would have observed an image similar to the one shown below. Which of the following statements is a valid conclusion from the observations made in this Maltese Cross investigation? (a) Cathode rays pass through the glass. (b) Cathode rays pass through metals. (c) Cathode rays are charged particles. (d) Cathode rays travel in straight lines. - 3 -
11. In class you performed a first- hand investigation investigating the occurrence of different striation patterns for different pressures in discharge tubes. The apparatus used is shown below. (a) Identify any safety issues associated with this experiment. (b) Using a table compare the striation patterns in the different tubes as the pressure in the tube is decreased. (c) What is the function of the induction coil in this experiment? - 4 -
12. Explain how are electrons produced in the electron gun? 13. Compare the methods used to control the movement of the cathode ray beam in a CRO and a television set. 14. Outline the role played in the cathode ray tube by: (a) the applied voltage and the electrode in the electron gun (b) the electric field supplied by deflection plates, for example in a CRO (c) the current carrying coils, for example in a television (d) the fluorescent screen - 5 -
15. Explain why the fluorescent screen glows when struck by an electron. 16. What are the two functions of the anode in a cathode ray oscilloscope? 17. Explain the mechanism by which the brightness is adjusted in a cathode ray oscilloscope. 18. Identify the following components of a cathode ray oscilloscope by labelling the diagram below: (a) horizontal deflecting plates (b) vertical deflecting plates (c) anode (d) cathode (e) electron gun (f) cathode ray (g) phosphor screen - 6 -