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Turning Points in Physics Active Recall Answers
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Answers to the Turning Points in Physics Active Recall Questions
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Turning Points Active Recall ANSWERS:1. What is a cathode ray tube? A discharge tube with a potential difference
applied across it, with a low pressure gas
inside it
2. What is a cathode ray? A beam of electrons, seen as a glow.
3. What does a cathode ray Glowing tube
look like?
4. Where does the ray glow the At the cathode. The gas ions and electrons
brightest? Why? recombine and emits photons of light.
5. What four properties do Mass, negative charge, same properties no
cathode rays have? matter the gas used in the discharge tube,
large charge to mass ratio.
6. What was it concluded that Electrons
cathode ray particles were?
7. What is the process by which The high potential difference pulled
the discharge tube begins to electrons of the gas particles, forming ion
glow? and electron pairs. The positive gas ions
accelerate towards the cathode and when
the collide with the cathode, they release
even more electrons. The electrons
accelerate along the tube and collide with
gas atoms causing them to be excited.
These excited gas atoms quickly de excite
and release photons of light.
8. How are ion and electron The high potential difference pulls
pairs formed in the discharge electrons of the gas atoms.
tube?
9. Where is the gas ions Cathode
accelerated towards?
10.What happens when the gas They release even more electrons.
ions collide with the cathode? Thermionic emission, as the collisions heat
Why? the cathode up allowing it released
electrons.
11.When electrons formed from They collide with gas atoms and excite
gas ions are accelerated them, so when they de excite they emit
along the tube what photons of visible light.
happens?
12.How is the glow produced? The excited gas atoms de excite and
produce photons of visible light.
13.What is thermionic emission? When a metal is heated until free electrons
on its surface gain enough energy to be
emitted.
14.How does an electron gun They have a potential difference which
use thermionic emission? accelerates electrons to the cathode,
which heats up and can emit electrons.
These are then accelerated to the anode,
which will have a small gap that the
electrons pass through and create a
narrow beam.
15.What is the equation for work Work done = QV
done on a charged particle in
an electric field?
16.What is the work done on an eV=Work done
, electron accelerated through
a potential difference?
17.As an electron moves from Electric potential energy is converted to
the cathode to an anode in kinetic energy so the the electron speeds
an electron gun which up.
energy does it originally have
that it is converted to? What
does this make the electrons
do?
18.When an electron reaches an Kinetic energy is equal to work done
anode, its kinetic will be therefore eV=1/2mv2
equal to what?
19.What is a fine beam tube? Low pressure gas that has a uniform
magnetic field passing through it.
20.What happens when you If the electrons enter a fine beam tube
released electrons from an perpendicular to the direction of the
electron gun into a fine beam uniform magnetic field, the electrons will
tube? act in a circular path, as the magnetic
force acts as the centripetal force.
21.When electrons move They collide with gas atoms, causing them
through the fine beam tube, to be excited and de excite therefore
how do they interact with the releasing photons of visible light, meaning
gas atoms in the tube? What the path of light is visible.
does this cause the gas
atoms to do?
22.Why can the radius of the The gas atoms release photons of visible
circular path of the electrons light, so their path can be seen, therefore
be measured in a fine beam the radius of their circular path can be
tube once accelerated into measured.
from an electron gun?
23.Using the fine beam tube
experiment, derive the
equation for specific charge
24.Which three main equations
are used to derive the
specific charge using the fine
,
beam tube method?
25.What is Thompsons crossed A magnetic and electric field are
fields? perpendicular to each other, therefore
deflect the electrons in opposite directions.
26.When electrons are Upwards by electric and downwards by
accelerated into the crossed magnetic.
fields, which direction does
the magnetic field deflect the
electrons and which direction
does the electric field deflect
the electrons?
27.What is done to the strength Strengths adjusted until electron beam
of the fields? What is the passes through the crossed field
desired effect by adjusting undeflected. Therefore the electric and
the fields? magnetic field strengths are equal and
opposite in directions.
28.By adjusting the fields, what Equal and opposite directions.
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