From Ideas to Implementation
Curriculum revision lecture pre- and post-work
Complete the following pre-work prior to attending the videoconference lecture. After
the presentation, reflect on your responses then try the post-work questions.
Pre-work
1.
Define the following terms to the wave model:
anode
capacitor
cathode
coherent
composite video signal
oscillating
pixel
phosphors
photocathode
positive electrode
raster scan
standing wave
RURAL AND REMOTE EDUCATION – A BLUEPRINT FOR ACTION 10.2
2.
Two parallel plates having a potential difference of 1000 V are separated by a gap of 0.02 m. What is the strength of the
electric field between the plates?
3.
A charge of +6 pC enters an electric field of 50 000 NC-1 acting between two parallel plates. What is the size of the force
acting on the charge.
4.
Two parallel conducting plates separated by 0.1 m have a potential difference of 100 V between them. What is the strength
of the electric field between the plates?
5.
What is the potential difference at a point mid way between the plates from the question above with respect to the positive
plate? Explain your answer.
6.
Label the following diagram
RURAL AND REMOTE EDUCATION – A BLUEPRINT FOR ACTION 10.2
7.
Gas discharge tubes were invented when the air pump could evacuate the air well enough to allow the gas in the tube to
conduct an electric current.
The phenomenon that appears in gas discharge tubes is pressure dependent. Some of the features that occur include:
8.
A systematic study of Crookes’ tubes showed the behaviour of cathode rays that were evidence that the rays were both of
a wave like character and a particle like character.
The evidence for a wave nature was:
The evidence for a particle nature was:
9.
The formula to describe the force acting on a moving charge in a magnetic field is:
10. The formula to describe the effect of an electric field on a charge between two parallel charged plates is:
11. What properties of cathode rays are demonstrated by discharge tubes:
a) containing a Maltese cross.
b) with a fluorescent display screen.
c) containing a glass paddle wheel.
12. An electron (-1.6 X 10-19 C) is moving between two parallel oppositely charged plates that create an electric field strength of
100 NC-1. What is the size of the force acting on the charge and in which direction is the force acting?
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13. Calculate the force acting on a electron entering a magnetic field of 4 T at 90° to the magnetic field if the velocity of the
electron at entry was 2000 ms-1.
14. Describe the path taken by an alpha particle (positively charged) as it passes between the poles of a large horseshoe
shaped magnet. The alpha particle enters the magnetic field at 90°. Explain your answer with a diagram.
15. A proton with a charge of 1.6 X10-19 C travelling with a velocity of 106 ms-1 enters a magnetic field at an angle of 30° to the
direction of the magnetic field. The magnetic field strength is 0.5 T.
Calculate the magnitude of the force acting on the proton.
16. A) If the direction of the magnetic field for the previous question is directly down the page and the proton enters the field
from the right of the magnetic field, in which direction will the force act as the proton enters the field?.
B) Will the direction of action of the force in the example above remain constant throughout the passage of the proton
through the magnetic field? Explain your answer.
RURAL AND REMOTE EDUCATION – A BLUEPRINT FOR ACTION 10.2
17. An oscilloscope is particularly good for studying regularly fluctuating voltages in electrical circuits or electronic equipment.
After considering how the oscilloscope works, propose reasons why this tool should be so useful for this purpose.
18. Outline the sequence of events that led to the development of the CRO with particular reference to the development of an
increased understanding of cathode rays.
19. The cathode ray tube in an oscilloscope, television and electron microscope have a number of features in common.
List the common features. Describe the common role each feature has in the operation of the device.
20. Describe how the magnetic fields used in television sets control the production of the image.
21. What is the role of the electron gun in a television?
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22. An image can be created on the screen of a black and white television even though the size of the dot produced by the
electron beam at any instant of time is at a maximum the size of a pin head. Explain how this is possible by referring to the
characteristics of the screen and the human eye. Discuss the role of magnetic fields in making the image possible in your
answer.
RURAL AND REMOTE EDUCATION – A BLUEPRINT FOR ACTION 10.2
Post-work
Test how well your understanding has improved by completing the following questions after the
videoconference lecture.
23. In a vacuum tube an electron with a charge of -1.6 X 10-19 C travelling at 1 X 105 ms-1 enters an electric field of 1 NC-1
between two 0.5 cm long horizontally placed parallel plates. The plates are 1.5 cm apart and the electron enters the gap
between the plates at right angles and at a point midway between the plates.
The mass of an electron is 9 X 10-31 kg. The arrangement of the equipment is shown in the figure below. Note that this
arrangement is similar to the operating principle of a working television. The screen is 0.2 m away from the end of the
plates.
Calculate:
a) The force applied to the electron by the electric field between the plates.
b) The acceleration of the electron due to the force produced by the electric field.
c) The velocity change that will occur to the electron as a result of the applied force acting over the full length of the plates.
(Hint: calculate the time it takes to travel through the full length of the plates.)
RURAL AND REMOTE EDUCATION – A BLUEPRINT FOR ACTION 10.2
d) The electron continued on its path toward a screen located 0.2 m from the exit end of the parallel plates. That screen
had a horizontal line drawn on it parallel with the middle of the separation distance for the two plates. Describe
quantitatively where on the screen it would hit.
(Hint: find the vertical displacement that occurs within the field first, then calculate the vertical displacement after it leaves
the field.)
24. Imagine you were to bring the north pole of a bar magnet directly in front of a cathode ray tube, where the cathode was
located on the left of the page and the anode on the right. Which way would the cathode beam deflect?
25. Explain why Thomson was able to determine the charge to mass ratio in his famous experiment using cathode rays but
could not measure the mass nor the charge by themselves accurately.
RURAL AND REMOTE EDUCATION – A BLUEPRINT FOR ACTION 10.2
Further information
Learning and Leadership
Directorate
Science Advisor
Level 3, Oxford Street
Darlinghurst NSW 2010
CAASTRO in the Classroom
Sydney University
citc@caastro.org
www.caastro.org/citc
© February 2014
NSW Department of Education and Communities
RURAL AND REMOTE EDUCATION – A BLUEPRINT FOR ACTION 10.2