Some Interesting/Effective Physics Experiments for
Pre-University Students
Foong See Kit1, Ho Seng Yong2,3, Lim Chim Chai2, Lin Kai2,4, Loganantham Kuppan1,2
1
Natural Sciences and Science Education, National Institute of Education,
Nanyang Technological University, 1, Nanyang Walk, Singapore 637616
2
Centre for Research in Pedagogy and Practice, National Institute of Education,
Nanyang Technological University, 1, Nanyang Walk, Singapore 637616
3
Currently PhD candidate in physics at University of Toronto
4
Currently 2nd year physics student at Cambridge University
Some objectives of physics education:
1.
Help to inculcate proper character and perspective among students. E.g.
objectivity, inquisitiveness, patience, determination, clarity and
impartiality.
2.
To educate students so that they are able to better appreciate the relation
between human beings to their environment. E.g. role and relation of
human being to other living things and his physical environment.
3.
To educate students so that they are able to consider alternative methods of
project development and choose the most efficient and effective means of
development.
4.
To educate students so that they are able to make use of the principles of
physics in the development of products that are beneficial to mankind.
In teaching physics, school experiments are used to
•
arouse and sustain the students’ interest in the learning of the subject
•
facilitate the teaching of various principles and concepts
•
repeat well-known experiments and verify known results in basic physics
•
demonstrate various phenomena
The experiments shown are some of those that are being tried out in the teaching
of physics at pre-university level in Singapore. We try to make use of easily
available inexpensive materials without the need for expensive equipments. They
may be adapted for use in different countries.
Induced emf due to a swinging ferromagnetic
material
Computer
Strings about 0.5m long
Datalogger
Iron bar
Voltage sensor
N
Search Coil with 400
turns of wire
Magnet
Objective :
Iron bar oscillating past a search coil in the vicinity of a magnetic field.
To investigate if emf would be induced when magnetic flux changes
even without relative motion between pemanent magnet and
induction coil.
Special features:
To instill an enquiry attitude, and to show that it is possible to
induce an emf in an induction coil without having relative motion
between induction coil and permanent magnet. It is achieved by
passing a soft iron bar in the vicinity of the permanent magnet,
thereby causing the magnetic field in the region to vary.
Procedure:
1. Set up the apparatus as shown using a magnet, a small iron bar, a
string (0.8 m long) and search coil with 400 turns of wire.
Suspend an iron bar from a height of about 0.8 m such that it is
oriented vertically facing the coil. Make adjustments such that
the iron bar maintains its oscillation in a plane. Position the
magnet vertically with the North pole nearer to the search coil.
2. Predict how the induced emf E in the search coil will vary with
time for one complete oscillation of the iron bar.
3. When the oscillation of the iron bar stabilises, click “record” at
the computer to start recording the variation of E.
4. Note the time interval between successive peaks.
5. Determine the period of oscillation of the iron bar.
6. Examine the period obtained from steps 4 and 5, and establish
their relationship.
Result:
Typical computer plot
Induced e.m.f, E /
V
Projectile on inclined plane
Steamer causing
condensation on
perspex surface
Track left by
steel ball
u
H
θ
φ = 40ο
R
Objectives:
To enable the students
1. To appreciate the convenience of resolving a vector such as a
velocity vector into two mutually perpendicular components.
2. To analyse the factors affecting the trajectory of a projectile:
both the projection angle and the Perspex’s angle of inclination
can be varied.
Special feature:
The track left by the steel ball depicting the trajectory of the
projectile is visible to students. Maximum height and range can be
measured directly.
Procedure:
1. Set up the perspex such that it is inclined at an angle φ of about
40o to the horizontal. Refer to the figure.
2. Clean the piece of perspex provided such that the surface where
steam is to be condensed is free of dirt and stain. Direct the
steamer at the perspex from a distance of about 5 cm away
(excessive heating will cause the perspex to bend). Apply until a
layer of steam condenses evenly on the surface of the perspex.
3. To study the variation of R and H with θ, the ball bearing has to
be projected at always nearly the same velocity, u. This can be
achieved by means of a launcher which can be improvised with a
pen that has a spring as shown below.
4. Repeat Step 3 above with a different angle of inclination φ.
Steel ball
Spring
release
θ
Results:
Range R vs sin2θ
φ = 40
2
Maximum Height H vs sin θ
φ = 40
0.450
0.180
y = 0.3331x + 0.002
2
R = 0.9915
0.400
0.350
y = 0.1731x - 0.0018
2
R = 0.9991
0.160
0.140
0.120
0.250
0.100
H
R
0.300
0.200
0.080
0.150
0.060
0.100
0.040
0.050
0.020
0.000
0.000
0.200
0.400
0.600
0.800
sin2θ
1.000
1.200
1.400
0.000
0.000
0.200
0.400
0.600
0.800
2
sin θ
Sources of errors:
1. The steel ball may loose contact with top of the compressed
spring when it is accelerated outward by the spring before the
spring fully regain its original length.
2. In addition to translational motion, the steel ball also has
rotational motion when it is gliding along the surface of the
Perspex sheet.
3. The steel ball is elevated by the compressed spring during
projection. The amount of elevation differs slightly depending
on the angle of projection θ.
1.000
Illustration of action of a bridge rectifier using
Light Emitting Diode (LED)
Objective :
Typical bridge rectifier circuit
The direction of flow of current in a diode cannot be visually seen.
With LED replacing the normal diode, the LED lights up whenever
current is flowing through it in forward direction. This allows the
action of a bridge rectifier to be visually seen by students.
Special Feature :
The action of the 4 diodes, which are working in pairs of green (G1,
G2) or yellow (Y1, Y2) as shown, can be visually seen when one of
the pairs of LED is allowing the current to flow in the forward
direction and another pair stops the current from flowing in the
reverse direction. The load (red LED) in the middle lights up when
either pair is in the forward direction.
Procedure:
Setup the circuit as shown.
Since a low voltage ac source is not readily available at this poster
session, we improvise it with a low voltage dc source and a pair of
double-throw switches to allow the polarity of the supply voltage to
be reversed.
In an actual laboratory condition, if the ac source is supplied by a
signal generator with variable frequency control, the visual impact
on students will be good especially at a frequency of about 0.5Hz.
A low value resistor is recommended to be included in the circuit if the
supply voltage is higher than 10V, in order not to damage the LED.
This illustration, with ac source, has also appeared in an article by Juan
A. Pomarico (THE PHYSICS TEACHER, Vol. 40, February 2002).
Ballistic pendulum: Applying conservation of
momentum to determine speed of a fast moving
object
Figure 1: Experimental setup of ballistic pendulum
Plastic cylinder with pointer stick
and a meter-rule below, which
helps in the reading of Lmax
Objectives:
1. To appreciate how conservation of momentum can be used to
measure the speed of a small fast moving object.
2. Students will be able to do simple calculations related to the
conservation of momentum and make modifications to the
apparatus for other applications such as the speed of ‘bullet’
from a toy gun.
Procedure:
PartA
1a. Record the mass M of the plastic cylinder (including its content),
and the mass m of the metal ball. Set up the experiment as
shown in Fig.1.
2a. Let a small metal ball roll down the plastic tubing fixed with a
flexible rubber hose at the outlet end. This small metal ball is
like a bullet in our analysis. At the end of the tubing, the metal
ball is projected horizontally with velocity u1 and “caught” by a
plastic cylinder. This plastic cylinder is closed at one end and
filled with sponge which is attached to the cylinder with a
double sided tape. The speed u1 of the metal ball is altered by
changing the height H. A small pointer stick attached to the
closed end of the plastic cylinder is
used to indicate the maximum
horizontal distance swept through,
Lmax. hmax can then be computed as
shown.
3a. Place a meter-rule directly below the plastic cylinder (Fig.1).
4a. Release the metal ball from H=1.00m and record the
corresponding Lmax.
5a. Calculate the speed u1 of the metal ball when it leaves the rubber
tubing. Using the principle of conservation of linear momentum
as well as conservation of energy
u1 =
(M + m )
m
2ghmax
,
6a. Repeat step 4a. to 5a. above for different values of H.
Part B
1b. The accuracy of computing the speed of the fast moving metal
ball can be checked as
follows:
2b. The plastic tube together with
the flexible rubber hose is
transferred to a table top
approximately 0.8m above the
floor (Fig.2).
Figure 2 : Experimental setup of projectile method
3b. The metal ball is released from the top of the plastic tube with
H=1.00m as in 4a.
4b. The metal ball will shoot out from the end of the flexible rubber
hose and drop onto a piece of carbon paper, leaving a mark on
the piece of white paper which is laid below the carbon paper.
Measure the horizontal distance x. Compute the speed of
projection of the metal ball u2 using the equation
g
u2 = x
2y
.
5b. Repeat 3b. to 4b. with the same set of values of H as in 6a.
6b. Plot the graphs: a) u12 and
u22
vs H
and b)
u1
vs u2 .
Result:
From graph c), the accuracy of the speed obtained from the ballistic
pendulum method is about 91% compared to the projectile method.
speed square of the steel ball ((u_1)^2 and (u_2)^2) against H/m
u1 against u2
speed square of
the steel ball
10.00
3.50
y = 11.712x - 1.2417
R 2 = 0.9793
9.00
3.00
8.00
y = 0.9115x + 0.0477
R2 = 0.9385
2.50
7.00
6.00
(u_1)^2
5.00
(u_2)^2
4.00
2.00
u1
1.00
y = 10.407x - 1.2437
R2 = 0.9712
3.00
0.50
2.00
0.00
-0.50
0.00
-0.50
1.00
0.00
0.30
1.50
0.40
0.50
0.60
0.70
H/m
0.80
0.90
1.00
0.50
1.00
1.50
u2
2.00
2.50
3.00
3.50
Natural frequency and resonance
Oscillator
Signal Generator
Mass on spring attached to a driver
Objectives:
Resonance of a spring-mass system
1. To appreciate the concept of natural frequencies of a system.
2. To appreciate the concepts of driver frequency of an oscillating
system and condition(s) required for the occurrence of resonance.
Special features:
1. Students are able to observe resonance and we believe they
will gain a strong impression of the phenomena.
2. Students are guided by questions to conclude on their own the
condition(s) for resonance to occur in a vibrating system.
Procedure:
PartA:
1a. Set up the experiment as shown. Supply a low driving
frequency to the mechanical driver which would force the
spring-mass system (spring S1, mass m1) into vibration. Note
the amplitude of vibration of the mass.
3a. Tabulate the data for the
amplitude of the vibrating mass
against the driving frequency
and plot the graph as shown.
Amplitude/cm vs driving frequency/Hz
60
55
50
45
Amplitude/cm
2a. Slowly increase the driving
frequency of the mechanical
driver,
and
note
the
corresponding amplitude of the
vibrating mass.
40
35
30
25
20
15
10
5
0
0
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
1
1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9
Driving frequency/Hz
2
2.1
4a. Determine from the graph the driving frequency that would
produce the maximum amplitude of the vibrating mass. Call it f1.
5a. Repeat step 2a to 4a with a different mass (m2). Call the
frequency determined as f2.
6a. Repeat step 2a to 4a using a spring of different stiffness (S2)
and mass (m1). Call the frequency determined as f3.
PartB:
1b. Repeat the experiments with the mechanical driver switched off.
2b. With a mass attached to the spring, release the mass from a
point a few cm below the equilibrium position to allow the
system to vibrate naturally. Using a stop watch, time the period
required for 20 complete vibrations. Calculate the frequency of
this natural vibration.
3b. Tabulate the results from PartA and PartB :
PartA – vibration
with driver
PartB – natural
vibration
f1
f2
f3
f 1'
f 2'
f 3'
'
'
'
4b. Establish a relationship between ( f1 , f 2 , f 3 ) and ( f1 , f 2 , f 3 ) and
guide the students to deduce that resonance would occur when
driving frequency matches the natural frequency of the
vibrating system.