Download 12Phyass15 Ideas to Implementation

YEAR 12 PHYSICS.
ASSIGNMENT #15.
Due Monday 8th April
Q1. (a) What is a “Geissler tube”? – use a diagram in your answer. [3]
(b) What was meant by the term “cathode rays”? [1]
(c) Why was it regarded as surprising that cathode rays could cross between the electrodes? [1]
(d) What is one way of proving they come out from the cathode? [1]
(e) How are cathode rays shown to possess momentum (or kinetic energy)? – include a
diagram. [3]
(f) What was significant about cathode rays possessing momentum? [1]
(g) Sketch the “Maltese Cross” experiment, and label it. [2]
(h) What property of cathode rays did this experiment demonstrate? [1]
(i) Contrast the “British view” and the “German view” of the nature of cathode rays. [2]
(j) State two pieces of evidence supporting the German view. [2]
(k) How was the impasse finally resolved? [1]
(l) What is today’s view of the nature of cathode rays? [2]
Q2. (a) Carefully sketch the electric fields surrounding:i/
a negative point charge; [1]
ii/ two positive point charges of equal strength about 2½ cm apart; [2]
iii/ two oppositely-charged point charges of equal strength about 2½ cm apart; [2]
iv/ two parallel plates about 1½ cm apart carrying potentials of +25 and –25 volts; [2]
v/
two parallel plates about 1½ cm apart carrying potentials of +150 and +100 volts. [1]
(b) What work is done by an electric field 1.00 cm wide, and with
+ + + +
a strength of 4000 V m-1 on an electron [qe = 1.60  10-19 C] as
electron
1.00 cm
–
.
–
–
–
it crosses from the negative to the positive plate? [2]
(c) Assuming all this work is converted into kinetic energy of the
electron, what is its speed as it reaches the positive plate? [2]
(d) What is the special property of the element selenium that enables it to be utilised in
photocopiers? [1]
(e) Explain how a photocopier photocopies. [2]
Q3. Consider the Thomson experiment. Initially we examine the velocity selector.
(a) Write down the magnitude and direction of the force acting on an electron as it passes
through an electric field of magnitude E newtons/coulomb, directed vertically upwards. [2]
(b) Write down the magnitude of the magnetic force acting on the electron as it passes with
velocity v m s-1 due east through a magnetic field of magnitude B teslas. [1]
(c) Identify how the magnetic field must be directed such that the deflection of the electron by
the electric field is annulled. [1]
E
[2]
B
(d) Hence show that v 
(e) Explain why the charge of the moving particle (even whether it is positive or negative) is
irrelevant in Thomson’s velocity selector. [1]
(f) Follow e above reasoning through to show that
q
E

[2]
m
r B2
(g) Thomson showed that the q/m ratio for cathode rays is 1.76  1011 C kg-1. He was then
able to discover that the q/m ratio for hydrogen is 9.6  107 C kg-1. Discuss the significance
of these values. [3]
(h) A beam of electrons is coming from behind you, and is striking
P
Q
this frame on the small circular target in the middle, directed
vertically into the page. Two plates, P and Q, provide an electric
field when they are switched on, and a magnetic field can also be
applied. When both of these fields are switched on, the electron
beam strikes the centre of the window
Identify which of the
plates, P or Q is positive. [1]
(i) Showing your reasoning, identify the locations of the north and south poles that produce the
magnetic field that contributes to the electron beam striking that window. [2]