GRADE 12 SCIENCE PAPER 1 PHYSICS - Amazon S3...12 56000 56000 8 7000 i s v N p F t N ' ' Example -1...
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Transcript of GRADE 12 SCIENCE PAPER 1 PHYSICS - Amazon S3...12 56000 56000 8 7000 i s v N p F t N ' ' Example -1...
GRADE 12 SCIENCE PAPER 1 PHYSICS
Question 2
Mechanics/Newton ‘s Laws ........................................................................................................................ 1
Question 3
Mechanics/Projectile motion ...................................................................................................................... 6
Question 4
Mechanics/Momentum ............................................................................................................................... 8
Question 5
Mechanics/Work ........................................................................................................................................ 10
Mechanics/Energy ...................................................................................................................................... 13
Question 6
Waves/Doppler Effect .............................................................................................................................. 14
Question 7
Electricity/Electrostatics ........................................................................................................................... 15
Question 8
Electricity/Circuits ..................................................................................................................................... 19
Question 9
Electricity/Electrodynamics...................................................................................................................... 21
Question 10
Materials & matter/Photoelectric effect ................................................................................................. 22
Paper 1 MEMOS/Question 2/Mechanics/Newton‘s Laws/Part of 42% 1
Paper 1 MEMOS
Question 2 Mechanics/Newton‘s Laws
Part of 42% RATIO PROBLEMS – page 2
Example There is a gravitational force F between
objects A and B at a distance R from each
other. What will the gravitational force be
if the mass of A is doubled and the distance
of separation made three times greater ?
Answer
2
2 2
2 2
2
3
2
3
2
9
A B Ai f
A B
i
km m k m mF F
R R
km m
R
F
NET GRAVITATIONAL FORCE – page 2
Example
363 ,
517 a
Three spheres li
nd 154
e stationary in a straight line.
The masses of the spheres are
Determine the magnitude and direction of the
net gravitatio ...
Sphere A
nal force
5.7
on
A
B C
m kg
m kg m kg
a
5
5
5
10 right
3.5 10 right Sphere B
Sph 9 10 er lefeC t
b
c
N
N
N
Answer
2
11
2
11 5
2
11
2
11 6
between A & B
?
363
517 6.67 10 363 517
0.5 0.5
6.67 10 5 10
between A & C
?
363
154 6.67 10 363 154
0.75 0.7
take right
5
6.67 10 6.6 10
AB A B
AB
ABA
B
AB
AB A C
AC
ACA
C
AC
F
F Gm mF
rm
m
r
G N
F
F Gm mF
rm
m
r
G N
5 6
5
:
5 10 6.6 10
5.7
as positive
10 right
net AB ACA F F Fa
N
Paper 1 MEMOS/Question 2/Mechanics/Newton‘s Laws/Part of 42% 2
2
11
2
11 5
2
11
2
11 5
between A & B
?
363
517 6.67 10 363 517
0.5 0.5
6.67 10 5 10
between B & C
?
517
154 6.67 10 517 154
0.25 0.2
take right
5
6.67 10 8.5 10
AB A B
AB
ABA
B
AB
AB B C
BC
BCB
C
BC
F
F Gm mF
rm
m
r
G N
F
F Gm mF
rm
m
r
G N
5 5
5
:
8.5 10
as p
5 10
3.5 10 righ
osit ve
t
i
net BC ABB F F Fb
N
2
11
2
11 6
2
11
2
11 5
between A & C
?
363
154 6.67 10 363 154
0.75 0.75
6.67 10 6.6 10
between B & C
?
517
154 6.67 10 517 154
0.25 0.25
6.67 10 8.5
r
10
take
AB A C
AC
ACA
C
AC
AB B C
BC
BCB
C
BC
F
F Gm mF
rm
m
r
G N
F
F Gm mF
rm
m
r
G N
6 5
5
5
:
6.6 10 8.5 10
9 10
9 10 l
ight as positi
e
v
t
e
f
net AC BCC F F Fc
N
N
Paper 1 MEMOS/Question 2/FORCE DIAGRAMS – page4/Part of 42% 3
FORCE DIAGRAMS – page4
normal force
F Gravitation (weight)
friction
F Applied force
N
g
T
F
f
sin cos
cossin
cossin
y x
TT
x Ty T
t a
s s
F F
FF
F FF F
normal force
F Gravitation (weight)
friction
F Vertical komponent of
pplied force
F Horizontal komonent of
pplied force
N
g
y
x
F
f
a
a
||
||
sin cos
sin cos
sin cos
g g
g g
g g g g
t a
s s
F F
F F
F F F F
||
normal force
friction
F Vertical komponent of weight
F Vertical komponent of weight
N
g
g
F
f
Paper 1 MEMOS/Question 2/FORCE DIAGRAMS – page4/Part of 42% 4
NEWTON’S PROBLEMS – page5
Example
o
A block of mass 1 kg is connected to another block of
mass 4 kg by a light inextensible string.
The system is pulled up a rough plane inclined at 30 to
the horizontal, by means of a constant
40 N force parallel to the plane as shown in the diagram
above.
The magnitude of the kinetic frictional force between the
surface and the 4 kg block is 10 N.
The coefficient of kinetic friction between the 1 kg b
lock
and the surface is 0,29.
State Newton's third law in words.
Draw a labelled free-body diagram showing ALL
the forces acting on the 1 kg block as it moves up
the incline. Calculate the magnitude
a
b
of the:
Kinetic frictional force between the 1 kg block and
the surface
Tension in the string connecting the two blocks
c
d
||
||
o o
For the 1kg block
sin cos
sin cos
sin cos
1 9.8 sin 30 1 9.8 cos30
g g
g g
g g g g
o a
h h
F F
F F
F F F F
||
||
o o
For the 4kg block
sin cos
sin cos
sin cos
4 9.8 sin 30 4 9.8 cos30
g g
g g
g g g g
o a
h h
F F
F F
F F F F
Answer
o
||
o
left
0.29 8.48take up as positive
2.46 up
0
1 9.8 cos30
8.48
for 1kg block
-
take up as positive
F
40 2.45 1 9.8 sin 30 1
32.6 1
for 4kg bloc
N
res
N g
N g
res
T g
a see
y axis f Fb
F ma N
F F
F F
N
c
x axis
ma
F f T F ma
T a
T a
||
o
2
k
-
neem 'op' as positief
F
10 4 9.8 sin 30 4
29.6 4
T=T Susbtitute a in 29.6 4
32.6 1 29.6 4 29.6 4 0.6
3.03 5 32.03
0.6 .
res
g
x axis
ma
T f F ma
T a
T a
let T a
a a
a N
a m s
Paper 1 MEMOS/Question 2/FORCE DIAGRAMS – page4/Part of 42% 5
ACTION-REACTION PAIRS – page 5
Paper 1 MEMOS/Question 3/Mechanics/Projectile motion/Part of 42% 6
Question 3 Mechanics/Projectile motion
Part of 42% PROJECTILE MOTION PROBLEMS-page6
Example
-1
A ball,A, is thrown vertically upward from a
height, h, with a speed of 15 mns .
AT THE SAME INSTANT, a second identical
ball,B, is dropped from the same height as ball A
as shown in the diagram below
a Calculate the time it takes for ball A to
return to its starting point
b Calculate
.Both balls
undergo f
the distance between
ree fall an
ball A and
d eventually hit the
ball B when ball A i
gro
s
und.
at its maximum height.
For ball A
For ball B
Answer
Take up as positieve
For upward motion
15
9.8 0 15 9.8
? 9.8 15
0 1.53
Time back to starting point
=1.53 2=3.06s
i f i
f
a
v v v g t
g t
t t
v t s
2
2
2
2
Time for ball A to reach maximum = 1.53s
For ball A
15 1
29.8
11.5306.. 15 1.53 9.8 1.532?
11.48 up
For ball B
0 1
29.8
11.5306.. 0 1.53 9.8 1.532?
11.48
11.48
ii
ii
b
vy v t g t
g
t
ym
vy v t g t
g
t
y
m
up
Distance between A & B
= 11.48 11.48
22.96m
Paper 1 MEMOS/Question 3/Mechanics/Projectile motion/Part of 42% 7
RELATIONSHIP BETWEEN GRAPHS
Example
-1
A boy stands at the edge of a high cliff. He throws a stone
vertically upwards with an initial velocity of 10 m·s . The
stone strikes the ground at a point below the cliff after 3,5 s.
The velocity-t
ime graph below was obtained from
measurements made during the motion of the stone.
Use the information on the graph to answer the following
questions:
Calculate the acceleration of the stone between a
-1
times t = 2 s and t = 3 s.
At which time s is the stone moving at a speed
of 5 m·s ?
After how many seconds does the stone reach its
highest point?
Determine the height of the cliff from which the
b
c
d
stone was thrown.
Using the top of the cliff as the initial position
of the stone, sketch the position-time graph
displacement-time graph for the motion of
the stone from its highest point until it
e
reaches
the ground. Only indicate relevant time values
on the x-axis.
Answer
1
2
1 1
2; 10 & 3; 20
10 2010 10 .
0.5 en 1.5s
(speed of 5m.s =velocity of +5m.s or -5
do
m.s )
wnward2 3
s
a
t
b
va m s
Highest point = positive area triangle 0-1s
Reaches maximum hight at t=1s
Upward motion = positive area
triangle 0-1s
1 1Height 1 10 5
2 2
Downward motion = negative area
triangle 1-3.5s
1Height
c
d
b h m
13.5 1 25 31.25
2 2
Height of the cliff 31.25 5 26.25
b h m
m
e
Paper 1 MEMOS/Question 4/Mechanics/Momentum/Part of 42% 8
Question 4
Mechanics/Momentum Part of 42%
MOMENTUM, CHANGE IN MOMENTUM & FORCE – page9
Example
-1
Two toy cars are moving on a horizontal plane.
Car A, weighing 0.8kg, moves to the left, in the
direction of car B, at 1.5m.s . Car B, weighing
1.2kg, is stationary. After the collision car A is
stati -1
a Determine the initial momentum of car A
b Determine the momentum of car B after
the collision
c
onary and car B is moving at 1m.s to the left.
)
)
) What is the momentum of car A after the
collision?
d Determine the change of momentum of car A
e Determine the average force that car B exerts
on car A, if the collision lasts 0.04 seconds
f How would the average force change
)
)
) if a
small cushion is attached to one of the cars
(before the collision)?
Answer
1
1
( )
1
11.2 0 0 . .
0 1.2
1.2
1.5
1.2
0.04
30
30 right
Smaller
Force is indi
Take left as positive
0.8 1.5 1.
rectly
2 . . left
0.8 0 0 . .
. . right
B
A f i
A
res
A
BopA
A
a p mv kg m s
p mv kg m
b p mv kg m s
c
p p p
s
kg m s
d
peF
t
N
f
proportional to time, when
change in momentum remains constant
The pillows will lengthen the time of the
collision (increase in time) and therefore
the force will decrease
8000 5 8000 12
56000
56000
8
7000
f f i i
res
p m v m v
N
pF
t
N
Example
-1 -1
A truck, weighing 8000 kg, reduces its speed
from 12m.s to 5m.s in 8 seconds.
The force required to do this
5 000N 12 000N
7 000N
is.
2
..
4 000N
A C
B D
Answer
8000 5 8000 12
56000
56000
8
7000
f f i i
res
p m v m v
N
pF
t
N
Paper 1 MEMOS/Question 4/Mechanics/Momentum/Part of 42% 9
FORMULA VS GRAPHS
Example Which one of the following momentum-time graphs
represent the motion of an object moving, from rest,
in a straight line under the influence of a constant
net force?
Answer
force is constante
the gradient of the straight line is also constant
res
resp
p
xy
F
t
m
t
F
Paper 1 MEMOS/Question 5/Mechanics/Work/Part of 42% 10
Question 5
Mechanics/Work Part of 42%
WORK WITH RESULTANT FORCE – page 12
Example
o
A man pulls a box with a mass of 25kg from rest
across a horizontal surface. He applies a constant
force of 40N, with an angle of 40 with the horizontal
axis. While in motion, the box experiences a co
nstant
friction force of 10N
Draw a free body diagram and show ALL
forces acting on the box
Give a reason why none of the vertical forces
perform any work on the box
Determine the net work done o th
.
n
a
b
c
e box when
it moves from A to B (5m apart)
Use the work-energy theorem to determine the
speed of the box when it reached B
The man now applies the same force, but with
a smaller angle with the horizontal
d
e
.
How does the work performed now (with the
smaller angle) relate to the answer in c)
Give a reason for your answer
(no calculation necess
ary)
oo
sin cos
cossin
cossin
40cos 4040sin 40
y x
Tt
x Ty T
o a
h h
F F
FF
F FF F
F Gravitation (weight)
friction
F Vertical komponent of pplied force
F Horizontal komonent of pplied force
g
y
x
f
a
a
e
Answer
o
normal force
F Gravitation (weight)
friction
F Applied force normal
The vertical forces are all 90 to the direction of
motion, so that W=F
forc
c
e
os 0
N
g
T N
a
b
F
f
x J
F
o
o
40cos 40 10
20.64 regs
determine F determine W
take right as positive cos
F 20.64 5 cos0
103.2
res net
net res
res x
N
W F x
c F f
J
o
o
o
o
determine W
cos
10 5 cos180
50 153.250
103.2
determine W
cos
5 cos 0
153.25
determine W
cos
5 cos 4
40 cos 40
0
153.2
40
x
x
T
x
T
f
f f
net f F
F
Fx x
net f F
F
F T
W F x
W W W
J
J
ORW F x
W W WJ
W F x
J
OR
0 153.2
103.2J
Paper 1 MEMOS/Question 5/Mechanics/Work/Part of 42% 11
2 2
22
2
2
1
=
1 1
2 2
1 1103.2 25 25 0
2 2
1103.2 25 0
2
8.256
2.9 .
If the angle decreases, then
cos will increase
and therefore the net work will
also increase
T
T
net K
net f i
f
f
f
f
net f F
F T
d W E
W mv mv
v
v
v
v m s
e W W W
W F x
WORK WITHOUT RESULTING FORCE - PAGE 12
Example
oMegan slides down a 10m slide that has a 30 angle
of elevation.
If she weighs 60kg and a frictional force of 26N is
present...
Draw a free body diagram
Determine the work done by friction
Determine t
a
b
c
he work done by gravity
Determine the total work done on Megan
Determine her velocity at the bottom of the slide
d
e
OR
||
normal force normal force
friction friction
F weight F Vertical component
of weight
F Vertical component
of weight
N N
g g
g
F F
f fa
Answer
o
cos
26 10 cos180
260
f fW Fb x
J
||
||
||
o
o
o
||
o
cos
10 cos 60
29
sin60 9.8
588 sin
sin
588sin 30588
588sin 30
40cos
10 cos 0
2940
g
g
F g
F g
g
g
g
g g
c
F mg OR o
h
FN
F
W F x
JW x
J
F
F
F
o
2 2
22
2
2
1
||
o260 2940
2680
cos
268 10 cos 0
2680
=
1 1
2 2
1 12680 60 60 0
2 2
1268
588sin 3
0 60 02
0 26
26
89.3
9.5 .
8
gnet f F
net res
net K
f i
f
re
f
f
s g
f
W W W
J
W F x
J
W E
mv mv
v
or F F fd
N
v
v
v m s
e
Paper 1 MEMOS/Question 5/Mechanics/Work/Part of 42% 12
WORK WITH NON-CONSERVATIVE FORCES-page12
Example
A stationary 5kg block is released from a
height of 5m. It slides down the frictionless
slope to point P. It then moves across the
frictionless horizontal plane PQ en finally
moves up a second rough s
1
urface QR where
it comes to rest at R, 3m above ground.
It experiences a constant friction force of 18N
while in motion. The speed at Q is 9.89
alculate the angle θ of the slope QR
94m.s
a C
Answer
2 2
2 2
o
1 1
2 2
1 15 0 5 9.8994
2 2
245
5 9.8 3 5 9.8 018 245 147
1475.44
cos
18 cos180
18
18
nc k p
k f i
p f i
nc k p
f
nc f
W E E
E mv mv
J
E mgh mgh
W E E
xN
x m
W f x
x
x
W W
x
in the triangle
sin =
3sin
5.44
33.5o
o
h
Paper 1 MEMOS/Question 5/Mechanics/Energy/Part of 42% 13
Mechanics/Energy Part of 42%
CONSERVATION OF ENERGY-page12
Example
A stationary 5kg block is released from a
height of 5m. It slides down the frictionless
slope to point P. It then moves across the
frictionless horizontal plane PQ en finally
moves up a second rough s
urface QR where
it comes to rest at R, 3m above ground.
It experiences a constant friction force of 18N
while in motion.
By using energy principles only, determine
the speed of the block at P
Explain
a
b why the kinetic energy is the same
at P and Q
Answer
( ) ( )
2 2
2 2
2
2
1
1 1
2 2
1 15 9.8 5 5 0 5 9.8 0 5
2 2
1245 5
2
98
9.9 .
PQ is a closed system (no friction)
mechanical energy is therefore conserved
meg voor meg na
Pi ki Pf kf
i fi f
f
f
f
f
E Ea
E E E E
mgh mv mgh mv
v
v
v
v m s
b
Paper 1 MEMOS/Question 6/Waves/Doppler Effect/11% 14
Question 6
Waves/Doppler Effect 11%
GENERAL DOPPLER EFFECT – page 15
Example
-1
Dolphins use ultrasonic waves to explore their
surroundings. When a dolphin is 100m from a
rock, it emits an ultrasonic wave with a frequency
of 250 kHz, while swimming at 20m.s towards
the rock. As
-1
a Calculate the frequency of the sound waves
that reach the rock
b When the dolphin is 50m from the rock
sume that the speed of so
, it
emits another wave o
und in water
f 250 kHz .
H
o
is 1500
w does
m.s .
this preceived frequency relate
to the answer is a)
Answer
3
1500
0
1500 020250 10
1500 20250253378?253
The same
The detected frequency is independent of
the distance between the source and the
observer
L
L S
SL
S
S
L
v v vaf f
v vv
v
f kHzHzf
kHz
b
CHANGES IN FREQUENCY – page 15
Example
The siren of a stationary ambulance emits ound
with a frequency of 700 Hz.
The driver of a car approaches the ambulance and
then passes it by. He perceives that the frequency
of the siren changes by
s
-1
a Name and state the wave phenomena
b Take the speed of sound in air as 340m.s
and calculate the speed of the car when it
passes the ambul
80Hz
ance
Answer
TOWARD
340
?
3400700
340 0700
?
AWAY
340
?
3400700
340 0700
?
340 34080 700 700
340 340
27200 340 700 340 700
27200 700 340 340
L
L S
SL
S
S
L
L
L S
SL
S
S
L
L L L
v v vf f
v vv
vv
f
f
v v vf f
v vv
vv
f
f
f f TOWARD f AWAY
v v
v v
v v
1
38.86 340 340
38.86 2
19.43 .
v v
v
v m s
Paper 1 MEMOS/Question 7/Electricity/Electrostatics/Part of 36% 15
Question 7
Electricity/Electrostatics Part of 36%
NET FORCE CALCULATIONS with only 3 forces in equilibrium – page 17
Example
8
A learner hangs a graphite covered,
polystyrene sphere T on the ceiling with a
light, inelastic string. The sphere carries a
charge of +4.8 10 and weighs 2g.
Next, the learner brings another identic
C
al sphere S,
mounted on an insulating stand, close to sphere T.
Sphere T comes to rest at a position 5cm away from
sphere S
Explain briefly why the polystyrene spheres
are covered with graphite
Calcul
a
b
ate the magnitude and direction of the
electrostatic force that sphere S exerts on
sphere T
Draw a free body diagram of all the forces
experienced by sphere T. Include the magnitude
of the forces wher
c
o
e they are known
Determine the tension in the string if it makes
an angle of 67 with the ceiling
d
Answer
Electrostatic force
F Gravitation
Tension in rope
E
g
F
T
1 2
2
9 8 8
2
3
2 2 2
22 3
2
Graphite is a good conductor - it ensures that
the charge is distributed evenly acros
9 10 4,8 10 4,8 10
0,05
8,29 10
repulsive
see top
0.0196 8
s the
sphe
.29 10
4.5 1
res
g E
a
kQ QbF
r
N
c
d T F F
T
4
o
0
0.02 67 to ceilingT N
Paper 1 MEMOS/Question 7/Electricity/Electrostatics/Part of 36% 16
NET FORCE CALCULATIONS with more than three forces – page 17
Example
8
A learner hangs a graphite covered,
polystyrene sphere T on the ceiling with a
light, inelastic string. The sphere carries a
charge of +4.8 10 and weighs 2g.
Next, the learner brings another identic
C
o
al sphere S,
mounted on an insulating stand, close to sphere T.
Sphere T comes to rest at a position 5cm away from
sphere S
Determine the tension in the string if it makes
an angle of 67 with the cei
d
ling
oo
sin cos
cossin
cossin
cos67sin 67
y x
xy
o a
h h
T T
TT
T TT T
TT
Answer
Electrostatic force
F Gravitation
T Vertical component of tension in rope
T Horisontal component of tention in rope
E
g
y
x
F
o
o
o
o
o 3
3 o
3
o
o
take up as positive
0 sin 67 0.0196
0.0196 sin 67
0.0196
sin 23
0.02 67 to ceiling
take left as positive
0 cos 67 8.29 10
8.29 10 cos 67
8.29 10
cos 67
0.02 67 t
res y g
res x E
y axis
F T F
T
T
T
N
x axis
F T F
T
T
T
N
o ceiling
Paper 1 MEMOS/Question 7/Electricity/Electrostatics/Part of 36% 17
NET FIELD – page 18
Example
1 2
1
2
Two charges,Q en Q , are placed a distance of
3m from each other. The charge on Q is -14 C
and the charge on Q is +20 C
Draw the electric field pattern due to these
two charges
Calculate the net e
a
b
2
lectric field at point P,
2m left of Q
Answer
1 2
9 6
2
1
2
2 2
9 6
2
1
1 2
1
1
1
9 10 14 10
1
126000 . left
9 10 20 10
2
45000 .
Take left as positive
126000 45000
171000 .
171000 . left
PQ
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Paper 1 MEMOS/Question 7/Electricity/Electrostatics/Part of 36% 18
RATIO PROBLEMS – page 18
Example The magnitude of an electric field, a distance r from a
point charge is E. The magnitude of an electric field,
a distance 2r from the same point charge will be …
1 1A E B E C 2E D 4E
4 2
Answer
2 2
2
2
2
4
1
4
1
4
i f
i
kQ kQ AE E
r r
kQ
r
kQ
r
E
Example
Two identical metal spheres, carrying charges Q and q,
are placed on insulating stands. At a distance of r
between them, they experience a force F. The two
spheres are now moved closer together so that the
distance between them is half of the original distance.
Which of the following best describe the force that they
experience at the new distance
1 12 4
4 2A F B F C F D F
Answer
2 2
2
2
1
2
1
4
4
4
i f
f
kQQ kQQ DF F
rr
kQQ
r
kQQ
r
F
Paper 1 MEMOS/Question 8/Electricity/Circuits/Part of 36% 19
Question 8
Electricity/Circuits Part of 36%
CIRCUIT PROBLEMS – page 20
Example
A battery is used to send current through three resistors.
What is the value of the emf of the battery?
Give a reason for your answer
A current of 3A flows through the 5 resistor,
when both switches
a
2
are closed. Calculate the
internal resistance of the battery
current passing through R
b
c
Answer
1
1 2
2
2 2 2
2
2
24V....it is the potential difference when no
current is flowing (S is open)
24 3 7
8 7
1
1 1 1
3 2
1 1 6
6 3
1
2
2
6 3
2
T T
P P P
P
P
P
a
b mf I R r
r
r
r
V I Rc
R R R
V
V V
R
V I R
I
I A
3
3
2
1 2
1 2
1 2
24 15 6
3 33
7 25
1
6 6
21 3 1 2
3 3 6 3
7 1
P
T P
T P
i
T i
T i
T i
mf V V
I II
R RR
r
V V
V V I I
I I R R
R r
3
1 2
3
1 2
3
1 2
1 1 1
T i
T P
P
T i P
P
T P
P
mf V V
V V V
V V V
I I I I
I I I
R R R
R R R
Paper 1 MEMOS/Question 8/Electricity/Circuits/Part of 36% 20
RATIO PROBLEMS –page 21
Example
2Switch S is opened. What happens to the
total resistance of the circuit
current passing through the circuit
the voltmeter reading over the battery
d
e
f
Answer i i T iT T
V I r mf V Vmf I R r
Resistance INCREASES, because the circuit
changes from parallel to series
Current DECREASES, becasue current and
resistance is indirectly proportional when emf
remains constant
The internal potential di
d
e
f fference decreases
(because current decreases), therefore the
total (external) potential difference increases,
so that the emf remains constant.
Paper 1 MEMOS/Question 9/Electricity/Electrodynamics/Part of 36% 21
Question 9
Electricity/Electrodynamics Part of 36%
CIRCUITS WITH ALTERNATING CURRENT – page 26
Example
A source supplies an rms-potential difference of 36V
to a 4 and 8 loudspeaker that is connected in series.
Determine the following
ms-current through the 4 loudspeaker
Peak current through ea
Ω Ω
a r Ω
b ch lo
udspeaker
Average power usage of the 4 loudspeaker
Without any further calculation, how will the
average power usage of the 4 loudspeaker
compare the average power usage of the 8
loudspeaker? G
c Ω
Ω
Ω
ive
d
a reason for your answer
Answer
1 2 1
2
2
2
4 8 336 12
12 3
2 3 4
3632
4.24
The power usage of the 4 is dubble the
power usage of the 8 loadspeaker
Power i
T wgk wgk T wgk
wgk
wgk
maks gemid wgkwgk
maks
maks
wgk
gemid
R R R V I R I Ia
AI
I A
Ib c P I RI
IJ
I A
d
VP
R
1 2
s inversely proportional to resistance
when potential difference remains constant
(The potential difference across R and R is the same)
Paper 1 MEMOS/Question 10/Materials & matter/Photoelectric effect/10% 22
Question 10
Materials & matter/Photoelectric effect 10%
PHOTOELECTRIC EFFECT PROBLEMS – page 28
Example
19
A learner, who wants to demonstrate the photoelectric
effect, uses a zinc plate fitted to the top of a gold leaf
electroscope. The work function of zinc is 6.9 10
Calculate the maximum wavelengt
J
a
h of light that
will emit electrons from the zinc plate
The electroscope is negatively charged and UV light is
shone on it. One of the wavelengths of the light is 260nm.
Calculate the kinetic energy ob f a photoelectron
emitted from the surface of the zinc plate
When the learner tries to replicate the experiment with
a positively charged electroscope, he finds that the UV
light has no noticeable effe
ct
Explain this observationc
19
o
34
8
6.9 10
?
6.63 10
3 10
?k
W J
h
c
E
Answer
o o
19 34
o
15
o
8 15
7
8 9
15
34 15
19
o
19 19
20
6.9 10 6.63 10
1.04 10
3 10 1.04 10
2.88 10
3 10 260 10
1.15 10
6.63 10 1.15 10
7.65 10
7.65 10 6.9 10
7.5 10
The p
k
k
k
E hfa
W hf
f
f Hz
c f
m
c fb
f
f Hz
E hf
J
E W E
E
E J
c
ositively charged zinc plate will attract
electrons and the emision of photo-electrons
will be prevented
