Transcript Experiments in L.C. Physicsx

Experiments in L.C. Physics
By a Gentleman
TO SHOW THAT a F
Dual
timer
t1
Light
beam
Air
track
Photogate
Pulley
l
Card
s
Slotted
weights
TO SHOW THAT a F
t1
Dual
timer
Photo
gate
Light
beam
t1 time for card to pass
first photo-gate
TO SHOW THAT a F
t1
t2
Dual
timer
Photo
gate
Light
beam
t2 time for card to pass
second photo-gate
Procedure
Set up the apparatus as in the diagram. Make sure the
card cuts both light beams as it passes along the track.
Level the air track.
Set the weight F at 1 N. Release the vehicle.
Note the times t1 and t2.
Remove one 0.1 N disc from the slotted weight, store
this on the vehicle, and repeat.
Continue for values of F from 1.0 N to 0.1 N.
Use a metre-stick to measure the length of the card l
and the separation of the photo gate beams s.
l
u
t1
F/N
1/.
t1/s
l
v
t2
t2/s
v u

2s
2
a
V/m/s
U/m.s
2
A/m/s2
Remember to include the following table to get full marks.
All tables are worth 3 marks when the Data has to be
changed. Draw a graph of a/m s-2 against F/N Straight
line though origin proves Newton's second law
VERIFICATION OF THE PRINCIPLE OF
CONSERVATION OF MOMENTUM
t1
l
Dual
timer
Photogate
Light
beam
Card
Air track
Vehicle 1
Velcro pad
Vehicle 2
1. Set up apparatus as in the diagram.
2. Level the air-track. To see if the track is level carry
out these tests:
a) A vehicle placed on a level track should not drift
toward either end.
Measure the mass of each vehicle m1 and m2
respectively, including attachments, using a balance.
4. Measure the length l of the black card in metres.
5. With vehicle 2 stationary, give vehicle 1 a gentle push.
After collision the two vehicles coalesce and move off
together.
6 Read the transit times t1and t2 for the card through
the two beams.
l
v
t2
l
u
t1
Calculate the velocity before the collision, and after
the collision,
momentum before the collision=momentum after the
collision,
m1u = (m1 + m2) v.
Repeat several times, with different velocities and
different masses.
MEASUREMENT OF g
Electromagnet
Switch
Ball bearing
h
Trapdoor
Electronic timer
When the switch opens the ball falls
The
timer
records
the time
from
when the
switch
opens
until trap
door
opens
When the switch opens the ball falls
The
timer
records
the time
from
when the
switch
opens
until trap
door
opens
Set up the apparatus. The millisecond timer starts when the
ball is released and stops when the ball hits the trapdoor
Measure the height h as shown, using a metre stick.
Release the ball and record the time t from the millisecond
timer.
Repeat three times for this height h and take the smallest
time as the correct value for t.
Repeat for different values of h.
Calculate the values for g using the equation . Obtain an
average value for g.
h  gt
1
2
2
Place a piece of paper between the ball bearing and the
electromagnet to ensure a quick release
VERIFICATION OF BOYLE’S LAW
Volume
scale
Bicycle pump
Tube with volume of
air trapped by oil
Reservoir of oil
Valve
Pressure
gauge
Using the pump, increase the pressure on the air in
the tube. Close the valve and wait 20 s to allow the
temperature of the enclosed air to reach equilibrium.
Read the volume V of the air column from the scale.
Take the corresponding pressure reading from the
gauge and record the pressure P of the trapped air.
Reduce the pressure by opening the valve slightly –
this causes an increase the volume of the trapped air
column. Again let the temperature of the enclosed air
reach equilibrium.
Record the corresponding values for the volume V
and pressure P .
Repeat steps two to five to get at least six pairs of
readings.
P
1/V
Plot a graph of P against 1/V.
A straight-line graph through the origin will
verify that, for a fixed mass of gas at constant
temperature, the pressure is inversely
proportional to the volume, i.e. Boyle’s law.
INVESTIGATION OF THE LAWS OF
EQUILIBRIUM FOR A SET OF CO-PLANAR FORCES
Support
Newton
balance
w1
w2
Newton
balance
w3
1. Use a balance to find the centre of gravity of
the metre stick and its weight.
2. The apparatus was set up as shown and a
equilibrium point found.
3.
Record the reading on each Newton balance.
4. Record the postions on the metre stick of
each weight, each Newton balance and the centre
of gravity of the metre stick
For each situation
(1) Forces up = Forces down
i.e. the sum of the readings on the balances
should be equal to the sum of the weights
plus the weight of the metre stick.
(2)The sum of the clockwise moments about
an axis through any of the chosen points
should be equal to the sum of the
anticlockwise moments about the same axis.
INVESTIGATION OF THE RELATIONSHIP
BETWEEN PERIOD AND LENGTH FOR A SIMPLE
PENDULUM AND HENCE CALCULATION OF g
Split
cork
l
Bob
Timer
20:30
1.
Place the thread of the pendulum between
two halves of a cork and clamp to a stand.
2. Set the length of the thread at one metre
from the bottom of the cork to the centre of
the bob.
3. Set the pendulum swinging through a small
angle (<10°). Measure the time t for thirty
complete oscillations.
4. Divide this time t by thirty to get the
periodic time T.
5. Repeat for different lengths of the
pendulum.
T2
l
T  4
g
T 2 4 2


 slope
l
g
4 2
 g 
(slope)
2
l
2
MEASUREMENT OF THE FOCAL
LENGTH OF A CONCAVE
MIRROR
Concave
mirror
Crosswire
Lamp-box
Screen
u
v
Approximate focal length by focusing image of window
onto sheet of paper.
Place the lamp-box well outside the approximate focal
length
Move the screen until a clear inverted image of the
crosswire is obtained.
Measure the distance u from the crosswire to the mirror,
using the metre stick.
Measure the distance v from the screen to the mirror.
Repeat this procedure for different values of u.
Calculate f each time and then find an average value.
Precautions The largest errors are in measuring with the
meter rule and finding the exact position of the
sharpest image.
VERIFICATION OF SNELL’S LAW
OF REFRACTION
Lamp-box
0 - 360° Protractor
i
Glass
Block
r
1. Place a glass block on the 0-3600 protractor in
the position shown on the diagram and mark its
outline.
2. Shine a ray of light from a lamp-box at a
specified angle to the near side of the block
and note the angle of incidence.
3. Mark the exact point B where it leaves the
glass block.
4. Remove the glass block. Join marks to trace
ray.
• Measure the angle of refraction r with
protractor.
• Repeat for different values of i.
• Draw up a table and Plot a graph of
sin i against sin r.
• The slope is refractive index, n
sin i
sin r.
MEASUREMENT OF THE
REFRACTIVE INDEX OF A LIQUID
Cork
Pin
Apparent depth
Mirror
Real depth
Water
Image
Pin
Finding No Parallax – Looking
Down
Pin at
bottom
Pin
reflection
in mirror
Parallax
No Parallax
Set up the apparatus as shown.
Adjust the height of the pin in the cork above the mirror
until there is no parallax between its image in the mirror
and the image of the pin in the water.
Measure the distance from the pin in the cork to the
back of the mirror – this is the apparent depth.
Measure the depth of the container – this is the real
depth.
Calculate the refractive index n= Real/Apparent
Repeat using different size containers and get an average
value for n.
MEASUREMENT OF THE FOCAL LENGTH
OF A CONVERGING LENS
Lamp-box with
crosswire
Screen
Lens
u
v
1.
Place the lamp-box well outside the approximate focal
length
2. Move the screen until a clear inverted image of the
crosswire is obtained.
3. Measure the distance u from the crosswire to the lens,
using the metre stick.
4. Measure the distance v from the screen to the lens.
5. Calculate the focal length of the lens using
1 1 1
 
f u v
6. Repeat this procedure for different values of u.
7. Calculate f each time and then find the average value.
MEASUREMENT OF THE WAVELENGTH
OF MONOCHROMATIC LIGHT
n=2
Metre
stick
n=1
Laser
θ
x
n=0
Diffraction
grating
D
Tan θ = x/D
n=1
n=2
1. Set up the apparatus as shown. Observe the
interference pattern on the metre stick – a series of
bright spots.
2. Calculate the mean distance x between the centre
(n=1) bright spot and the first (n =1) bright spot on
both sides of centre.
3. Measure the distance D from the grating to the
metre stick.
4. Calculate θ.
5. Calculate the distance d between the slits, using
d=1/N the grating number.
Calculate the wavelength λ using nλ = dsinθ.
6. Repeat this procedure for different values of n
and get the average value for λ
CALIBRATION CURVE OF A THERMOMETER USING
THE LABORATORY MERCURY THERMOMETER AS
A STANDARD
Multimeter as
ohmmeter
Mercury thermometer

Boiling tube
Water
Glycerol
Thermistor
Heat source
1. Set up apparatus as shown in the diagram.
2. Place the mercury thermometer and the
thermistor in the boiling tube.
3. Record the temperature , in C, from the mercury
thermometer and the corresponding thermistor
resistance R, in ohms, from the ohmmeter.
4. Increase the temperature of the glycerol by 5 C.
5. Again record the temperature and the
corresponding thermistor resistance.
6. Repeat the procedure until at least ten sets of
readings have been recorded.
7. Plot a graph of resistance R against temperature 
and join the points in a smooth, continuous curve.
MEASUREMENT OF THE SPECIFIC
HEAT CAPACITY OF A METAL BY AN
ELECTRICAL METHOD
12 V a.c.
Power supply
Joulemeter
10°C
350 J
Heating coil
Glycerol
Metal block
Lagging
1.
Find the mass of the metal block m.
2. Set up the apparatus as shown in the diagram.
3. Record the initial temperature θ1 of the metal block.
4. Plug in the joulemeter and switch it on.
5. Zero the joulemeter and allow current to flow until
there is a temperature rise of 10 C.
6. Switch off the power supply, allow time for the heat
energy to spread throughout the metal block and record
the highest temperature θ2.
7. The rise in temperature  is therefore θ2 – θ1.
8. Record the final joulemeter reading Q.
Energy supplied electrically = Energy gained by metal block
Q = mc.
MEASUREMENT OF SPECIFIC HEAT CAPACITY
OF WATER BY AN ELECTRICAL METHOD
10°C
12 V a.c.
Power supply
Joulemeter
350 J
Cover
Digital
thermometer
Water
Lagging
Calorimeter
Heating coil
1. Find the mass of the calorimeter mcal.
2. Find the mass of the calorimeter plus the water m1.
Hence the mass of the water mw is m1 – mcal.
3. Set up the apparatus as shown. Record the initial
temperature θ1.
4. Plug in the joulemeter , switch it on and zero it.
5. Switch on the power supply and allow current to
flow until a temperature rise of 10 C has been
achieved.
6. Switch off the power supply, stir the water well
and record the highest temperature θ2. Hence the rise
in temperature is θ2 – θ1.
7. Record the final joulemeter reading Q.
Electrical energy supplied = energy gained by (water +calorimeter)
Q
Precautions
=
mwcw θ
+ mcalccal. θ
1/. Lagging
2/. Cool water slightly so
final temperature not far from room temperature.
MEASUREMENT OF THE SPECIFIC HEAT
CAPACITY OF A METAL OR WATER BY A
MECHANICAL METHOD
Cotton wool
10°C
Boiling tube
Water
Digital
thermometer
Copper
rivets
Heat
source
Water
Lagging
Calorimeter
1. Place some copper rivets in a boiling tube. Fill a
beaker with water and place the boiling tube in it.
2. Heat the beaker until the water boils. Allow boiling
for a further five minutes to ensure that the copper
pieces are 100° C.
3. Find the mass of the copper calorimeter mcal.
4. Fill the calorimeter, one quarter full with cold water.
Find the combined mass of the calorimeter and water m1.
5. Record the initial temperature of the calorimeter
plus water θ1. Place in lagging
6. Quickly add the hot copper rivets to the calorimeter,
without splashing.
7. Stir the water and record the highest temperature
θ2.
8. Find the mass of the calorimeter plus water plus
copper rivets m2 and hence find the mass of the rivets
mco.
6. Quickly add the hot copper rivets to the
calorimeter, without splashing.
7. Stir the water and record the highest
temperature θ2.
8. Find the mass of the calorimeter plus water plus
copper rivets m2 and hence find the mass of the
rivets mco.
Heat lost by the Riverts=Heat gained by water and calorimeter
mco cco = mw cw + mc cc
MEASUREMENT OF THE SPECIFIC LATENT
HEAT OF FUSION OF ICE
10°C
Wrap ice in
cloth to
crush and
dry.
Crushed
ice
Calorimeter
Digital
thermometer
Water
Lagging
1.
Place some ice cubes in a beaker of water and keep until
the ice-water mixture reaches 0 °C.
2. Find the mass of the calorimeter mcal. Surround with
lagging
3. Half fill the calorimeter with water warmed to
approximately 10 °C above room temperature. Find the
combined mass of the calorimeter and water m2.
4. Record the initial temperature θ1 of the calorimeter plus
water.
5. Surround the ice cubes with kitchen paper or a cloth and
crush them between wooden blocks – dry them with the
kitchen paper.
6. Add the pieces of dry crushed ice, a little at a time, to
the calorimeter.
7. Record the lowest temperature θ2 of the calorimeter.
Find the mass of the calorimeter + water + melted ice m3
Calculations
Energy gained by ice =
energy lost by calorimeter
+ energy lost by the water.
mil +micw 1= mcalcc 2+mwcw 2
MEASUREMENT OF THE SPECIFIC
LATENT HEAT OF VAPORISATION OF
WATER
10°C
Steam
Trap
Digital
Thermometer
Lagging
Water
Calorimeter
Heat
source
1.
Set up as shown
2. Find the mass of the calorimeter mcal.
3. Half fill the calorimeter with water cooled to
approximately 10 °C below room temperature.
4. Find the mass m1 of the water plus calorimeter.
5. Record the temperature of the calorimeter + water θ1.
6. Allow dry steam to pass into the water in the
calorimeter until temperature has risen by about 20 °C.
7. Remove the steam delivery tube from the water,
taking care not to remove any water from the calorimeter
in the process.
8. Record the final temperature θ2 of the calorimeter
plus water plus condensed steam.
9. Find the mass of the calorimeter plus water plus
condensed steam m2.
Energy lost by steam = energy
gained by calorimeter + energy
gained by the water
msl+mscw ∆ = mcalcc ∆ +mwcw.∆
Joules law
10°C
A
Digital
thermometer
Calorimeter
Heating coil
Lid
Water
Lagging
Method
1.
Put sufficient water in a calorimeter to cover
the heating coil. Set up the circuit as shown.
2.
Note the temperature.
3.
Switch on the power and simultaneously start
the stopwatch. Allow a current of 0.5 A to flow for
five minutes. Make sure the current stays constant
throughout; adjust the rheostat if necessary.
4.
Note the current, using the ammeter.
5.
Note the time for which the current flowed.
6.
Stir and note the highest temperature.
Calculate the change in temperature ∆.
Calculation and Graph
Repeat the above procedure for increasing
values of current I, taking care not to exceed
the current rating marked on the rheostat or
the power supply. Take at least six readings.
Plot a graph of ∆(Y-axis) against I 2 (X-axis).
∆
I2
A straight-line graph through the origin verifies that
∆  I 2 i.e. Joule’s law.
Electrical Power lost as Heat P  I2 is Joules law
The power lost (Rate at which heat is produced) is
proportional to the square of the current.
RESISTIVITY OF THE
MATERIAL OF A WIRE
Micrometer
Nichrome
wire
Crocodile clips
l

Metre stick
Bench
clamp
Stand
Method
1. Note the resistance of the leads when the crocodile clips are
connected together. Could also be precaution.
2. Stretch the wire enough to remove any kinks or ‘slack’ in the
wire.
3.Read the resistance of the leads plus the resistance of wire
between the crocodile clips from the ohmmeter. Subtract the
resistance of the leads to get R.
4.Measure the length l of the wire between the crocodile clips,
with the metre stick.
5.Increase the distance between the crocodile clips. Measure the
new values of R and l and tabulate the results.
6.Make a note of the zero error on the micrometer. Find the
average value of the diameter d.
 R
1.
Calculate the resistivity ρñ    A,
2

d
l
where A =
4
2.
Calculate the average value for .
Precautions Ensure wire is straight
and has no kinks like ....
Take the diameter of the wire at
different angles
VARIATION OF THE RESISTANCE OF A
METALLIC CONDUCTOR WITH TEMPERATURE
10º C
10ºC
Ω
Digital
thermometer
Wire wound
on frame
Water
Glycerol
Heat source
Method
1.
Set up as shown.
2.
Use the thermometer to note the temperature
of the glycerol, which is also the temperature of the
coil.
3.
Record the resistance of the coil of wire using
the ohmmeter.
4.
Heat the beaker.
5.
For each 10 C rise in temperature record the
resistance and temperature using the ohmmeter and
the thermometer.
6.
Plot a graph of resistance against temperature.
Graph and Precautions
R

Precautions
- Heat the water slowly so temperature does not
rise at end of experiment
-Wait until glycerol is the same temperature as
water before taking a reading.
THE VARIATION OF THE RESISTANCE OF
A THERMISTOR WITH TEMPERATURE
10°C
Digital
thermometer
Ω
Water
Thermistor
Glycerol
Heat source
Method
1.Set up the apparatus as shown.
2.
Use the thermometer to note the temperature
of the glycerol and thermistor.
3.
Record the resistance of the thermistor using
the ohmmeter.
4.
Heat the beaker.
5.
For each 10 C rise in temperature, record the
resistance and the temperature using the ohmmeter
and the thermometer.
6.
Plot a graph of resistance against temperature
and join the points in a smooth, continuous curve.
Precautions
• Heat the water slowly so temperature
does not rise at end of experiment
• Wait until glycerol is the same
temperature as water before taking a
reading.
VARIATION OF CURRENT (I) WITH
P.D. (V)
A
+
6V
-
V
Nichrome
wire
Method
1.
Set up the circuit as shown and set
the voltage supply at 6 V d.c.
2.Adjust the potential divider to obtain
different values for the voltage V and
hence for the current I.
3.Obtain at least six values for V and I
using the voltmeter and the ammeter.
4.Plot a graph of V against I
Variations
(a) A METALLIC CONDUCTOR
With a wire
(b) A FILAMENT BULB
(c) COPPER SULFATE SOLUTION
WITH COPPER ELECTRODES
(d) SEMICONDUCTOR DIODE
Done both ways with a milli-Ammeter and the
a micro Ammeter
VARIATION OF CURRENT (I) WITH
P.D. (V)
mA
+
6V
-
V
Diode in
forward
bias
VARIATION OF CURRENT (I) WITH
P.D. (V)
A
+
6V
-
V
Diode in
Reverse
bias
MEASUREMENT OF THE
SPEED OF SOUND IN AIR
Tuning fork
l1
d
λ = 4(l1 + 0.3d)
Graduated
cylinder
Tube
Water
Method
1.
Strike the highest frequency (512 Hz)
tuning fork and hold it in a horizontal
position just above the mouth of the
tube.
2. Slide the tube slowly up from zero (To
get fundamental frequency) until the note
heard from the tube is at its loudest;
resonance is now occurring.
3. Measure the length of the air column
(from the water level to the top of the
tube) l1 with a metre stick.
• An end correction factor has to be added to the
length e = 0.3d, where d is the average internal
diameter of the tube (measured using a vernier
callipers).
• Hence λ = 4(l1 + 0.3d)
•
•
c = f
c = 4f(l1 + 0.3d).
• Calculate a value of c for each tuning fork and
find an average value for the speed of sound.
INVESTIGATION OF THE
VARIATION OF FUNDAMENTAL
FREQUENCY OF A STRETCHED
STRING WITH LENGTH
Tuning
Fork
Paper rider
l
Sonometer
Bridge
Place the bridges as far apart as possible.
Strike the turning fork putting the end on the
bridge and reduce the length until the maximum
vibration is reached (the light paper rider should
jump off the wire).
Measure the length with a metre rule.
Note the value of this frequency on the tuning
fork.
Repeat this procedure for different tuning forks
and measure the corresponding lengths.
Plot a graph of frequency f
against inverse of length 1
f
l
1
l
INVESTIGATION OF THE VARIATION
OF THE FUNDAMENTAL FREQUENCY OF
A STRETCHED STRING WITH TENSION
Tuning
Fork
Paper
rider
Pulley
Sonometer
Bridge
Weight
•Select a wire length l (e.g. 30 cm), by suitable
placement of the bridges. Keep this length
fixed throughout the experiment.
•Strike the tuning fork and hold it on the
bridge.
•Increase the tension by adding weight slowly
from lowest possible until resonance occurs.
(Jumping paper)
•Note tension from weight used (In Newtons)
and frequency from the tuning fork.
Plot a graph of frequency f
against square root of the tension
f
T
There you are and good
luck