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.  

 

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2. Identify  the  properties  of  cathode  rays  that  indicated  they  might  have  been  electromagnetic  waves.  Justify  each  property  as  characteristic  of  a  wave.  

 

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3. Identify  the  properties  of  cathode  rays  that  did  not  support  them  being  either  waves  or  particles.    

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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?    .......................................................................................................................................................................................  

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5. Describe  the  experiment  that  proved  the  existence  of  cathode  rays  as  a  stream  of  negatively  charged  particles.    .......................................................................................................................................................................................  

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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.    ......................................................................................................................................................................................    ......................................................................................................................................................................................    ......................................................................................................................................................................................      ......................................................................................................................................................................................    

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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.    

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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.  

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(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?    

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12. Explain  how  are  electrons  produced  in  the  electron  gun?    .......................................................................................................................................................................................  

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13. Compare  the  methods  used  to  control  the  movement  of  the  cathode  ray  beam  in  a  CRO  and  a  television  set.    .......................................................................................................................................................................................  

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14. Outline  the  role  played  in  the  cathode  ray  tube  by:    (a) the  applied  voltage  and  the  electrode  in  the  electron  gun  

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(b) the  electric  field  supplied  by  deflection  plates,  for  example  in  a  CRO    

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(c) the  current  carrying  coils,  for  example  in  a  television    .................................................................................................................................................................................      .................................................................................................................................................................................      .................................................................................................................................................................................  

(d) the  fluorescent  screen    

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15. Explain  why  the  fluorescent  screen  glows  when  struck  by  an  electron.    .......................................................................................................................................................................................  

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16. What  are  the  two  functions  of  the  anode  in  a  cathode  ray  oscilloscope?    .......................................................................................................................................................................................  

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17. Explain  the  mechanism  by  which  the  brightness  is  adjusted  in  a  cathode  ray  oscilloscope.    .......................................................................................................................................................................................  

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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