Sph 2182 physics for life sciences
B9- REFRACTIVE INDEX
LAWS OF REFRACTION
Aim: 1. Determination of refractive index of glass and water by
 plotting (graphical method) (glass)
 apparent depth method (water)
A. PLOTTING (GRAPHICAL METHOD)
APPARATUS
ABCD is a rectangular glass block.P1, P2, P3 and P4 are pins on a drawing board and paper.
i
P
B
A
r
E
F
C
D
i
P1
P2
Method
1. Place a rectangular glass block on a paper on the drawing board.
2. Draw line P as shown in the figure.
3. Look in along the direction of P 1 and P2 until the image of line P through the glass is in line with the pins.
4. Remove the pins and mark their positions on the paper.
5. Repeat the procedure for 5 more lines namely Q, R, S, T, and U. To get pins P 3 and P4, P5 and P6, P7 and P8 P9 and P10 and P11 and
P12. Make sure you mark the positions of the pins precisely.
6. Draw the outline of the glass block on the drawing paper.
7. Remove the glass block and pins from the paper.
8. Draw the normals at points E and F and join E&F.
9. Measure the angles i and R with a protractor, and calculate the refractive index. Repeat this for 5 more times and plot a graph of
sin i/sine r and get the refractive index of glass. Also calculate for each set of data sin i/sin r and get their average value. Compare
this with the one obtained from plotting.
I
Sin i
r
Sin r
Sin i/sin r
B. APPARENT DEPTH METHOD
Apparatus
Glass or Perspex block B, traveling microscope M, lycopodium powder L and beaker.
r1
fig
(b)).
(fig
(a)).
ethod
r3
r2
(fig (c)).




Place the beaker B on a sheet of paper P and arrange the travelling microscope so that the microscope M
and the scale s are vertical . Put a pin on the bottom of the beaker. Focus the microscope M on the pin.
Having achieved a sharp focus using the fine adjustment screw take the reading r3 (fig (c)). of the vertical
scale of the microscope.
NOW almost fill the beaker B with water. Move the microscope down until the pin seen through the water
is in sharp focus. Take the reading r2 fig (b)). of the vertical scale of the microscope.
Focus the microscope M on the upper surface of the water which is sprinkled using a little lycopodium
powder L or chalk dust if necessary Having achieved a sharp focus using the fine adjustment screw take the
reading r1 (fig (a)). Of the vertical scale of the microscope.
Repeat the procedure above for 5 more different depths of water and fill the table below.
Measurements
r1 (mm)
r2 (mm)
r3 (mm)
(r1-r2)
(mm)
(r1-r3) (mm)
1.
2.
3.
4.
5.
6.

Draw a graph of (r1-r3) (mm) versus (r1-r2) (mm) and find n for water graphically.
Conclusion:The refractive index of water is: Apparent method:…………+ ….%.The refractive index of
glass is: Plotting method:…………+ ….%.
W4 -THE RIPPLE TANK
AIMS: The aims of this experiment are:
1. To observe the characteristics and behavior of water waves.
2. To show the analogy between water waves and light waves.
APPARATUS
Water ripple tank, Metal reflectors , Low voltage power unit (3.0 V D-C) ,Ammeter ,Variable resistor, Motor
Vibrator, Lamp, Level.
INTRODUCTION
The ripple tank is an apparatus for studying the phenomena of water waves. The wave generator is a vibrator set
into motion by a 3V.D.C Motor. A variable resistor in series with the motor varies its speed and therefore the
frequency of vibrations. A lamp illuminates the wave pattern. The wave pattern is projected on the table through
the transparent bottom of tank. If one wishes to copy a wave pattern on paper the paper can be spread out on the
table under the ripple tank. When measuring wavelengths or other distances remember to measure these lengths
as they are in the ripple tank. For calibration place an object of known length on the bottom of the ripple tank
and measure the length of its image.The ripple tank should be leveled using the spirit level. Use so much water
that it stands midways on the sloping walls. The wave generator with wooden plate and motor has to be raised
or lowered so that the wave source just touches the water surface. The wave pattern can be ‘stopped’ by viewing
through stroboscope.
Single point source
1. Screw the bent metal rod onto the front of the place of the wave generator so that the rod points
forwards. Switch on the power and let the motor run slowly observe and draw a fig.1.
2. Place small pieces of paper on the water and see if they move. Are the pieces of paper displaced at the
wave speed? If not explain your observations.
3. Switch off the power and remove the bent metal rod. Lower the plane generator to touch just touch the
water surface.
4. Place the plane reflector at a small distance in front of the generator.
5. Observe the reflected pulse and draw a fig.2. Where is the center from which the reflected pulse seems
to diverge? Compare your observations with the plane mirror image of a light source.
6. Repeat step (3) using the two reflectors with a gap of 1-2cm between them observe and draw a fig.3 .
Where is the source from which the transmitted pulse seems to diverge? Compare your observation with
Huygen’s principle.
7. Place the metal parabolic reflector (convex side) so that the point source is at its focus. Give a single
push to the generator to produce a wave pulse. Observe (and draw a fig.4 ) the reflected pulse and
compare with the effect of a parabolic mirror when a light source is placed at its focus.
8. Repeat 7 metal parabolic reflector (concave side) observe and draw a fig.5
Two Synchronous point sources
Attach the two bent metal rods to the plate of the wave generator. Start the vibrator. Observe and observe and
draw a fig.4 the curves where the two waves interfere so that the water is at rest. Vary the frequency of the
waves by increasing the speed of the vibrator and observe observe and draw a fig.6 then explain the effect on
the interference pattern.
A Plane Wave
1. Use the plate of the wave generator itself as a source of waves. Produce waves with a wavelength about
2.5cm or to do this move the plate to and fro by hand.
2. Place the long reflector diagonally in the tank and observe reflected waves. Compare your observation
with the law of reflection for light observe and draw a fig.7.
3. Replace the long reflector by the two shorter reflectors parallel to the wave fronts 5-6cm away from the
wave generator and as far as possible from each other. Generate waves by hand or with the motor (about
2cm)observe observe and draw a fig.8. Decrease the distance between the two reflectors until about
1cm. Observe the wave fronts observe and draw a fig.9 then compare this with Huygen’s principle.
4. Place the very short reflector between the two reflectors so that two open spaces of 1cm or less are left
between the reflectors. Observe (and draw a fig.10) the interferences pattern and compare with the
results of experiment W4.2 and the experiment of Young.
5. Now remove the reflectors and put the rectangular plane block in the ripple tank at about 5cm from the
plane wave generator. The length of the block should parallel to the wave fronts observe and observe
and draw a fig.11.
6. Repeat 5 above with the block length about 450 to the wave front observe and draw a fig.12
The Report
The report should include the observations with carefully drawn neat figures and explanation where applicable
as well as answers to every question.
A4-HOOKES LAW
Introduction:
If an object is strained and released (or if an impulse is delivered), it will oscillate periodically about its
equilibrium or rest position. Examples of such objects are a saw blade clamped at one end, a mass attached to a spring,
a mass attached to a rod (torsional oscillations), musical string instrument; drum head, spider’s web, eardrum, and a car
body (oscillates vertically on its springs).
If during the oscillation, the elastic restoring force has a magnitude, which is proportional to the displacement
from the equilibrium position and a direction such as to restore the object to that equilibrium position, then the motion
is simple harmonic.
In this exercise you are going to perform a set of experiments to illustrate simple harmonic
motion using a spiral spring.
Apparatus
Spiral spring to which a light pointer is attached by plasticine at its lower end, rigid stand and clamp, meter rule, scale
pan and weights, stop watch.
a) To find the spring constant
If a spring is stretched a distance x which is not too large then the Hooke’s law states that the spring exerts a force F
which is proportional to x:
F = -kx………(1)
Where k is the force constant of the spring.
Method
The spring, with scale pan attached, is firmly clamped and the meter scale placed vertically so that the pointer moves
slightly over it (Fig 1). Place weights on the scale pan and measure the stretch produced in each case. The scale readings
are also taken when unloading the spring and the mean stretch thus obtained. Loads less than 1kg should be used as
more may permanently deform the spring. Plot the magnitude of the spring force (load) versus the stretch of the spring.
Fig.1
Question 1:
Is your graph describable by Hooke’s law? If so, determine the spring constant k.
Question 2:
Does your graph pass through the origin? If not, explain why.
Question 3:
From your graph what is the change in elastic potential energy of the spring when the load is increased from 0.5kg to
0.7kg?
b) To determine the acceleration of gravity (g) and the effective mass if the spring
Theory:
If a mass m is attached to a spring and the spring is extended by a further distance x a restoring force kx is called
into play. The spring on being released executes vertical oscillations the motion of the mass being
Md2x/dt2 = -kx
i.e.
d2x/dt2 + kx/M =0…. (2)
The motion is thus simple harmonic with periodic time T given by
T = 2π√ M/k…(3)
The above analysis assumes the spring to be weightless. In practice the spring has a mass and therefore a correction has
to be made to equation (3) to include the ‘effective’ mass of the spring.
Method:
A load is added to the pan, which is set in vertical vibration by giving it a small additional displacement. The periodic
time T is obtained by timing 20 oscillations. Repeat the experiment with different loads. Plot a graph of T2 versus load
and then find the values of g and m from it. Note that the mass of the scale-pan should be included in the load in this
experiment. Experimental errors must also be included.
Question 4:
Weigh the spring using a balance. What would you expect the effective mass of the spring to be using this measured
value? Compare it with the one obtained from the graph.
Question 5:
What is the percent discrepancy between your value of g and the expected value?
H18-HEAT CAPACITY OF METAL BLOCK
& SPECIFIC HEAT CAPACITY OF OIL
i.
ii.
HEAT CAPACITY OF A METAL BLOCK
SPECIFIC HEAT CAPACITY OF OIL, BY MIXTURES
APPARATUS
Large mass of metal (about 0.2kg) A, beaker B, copper calorimeter C in insulating jacket D, copper stirrer E, tripod,
gauze, burner, chemical balance, weights, oil (e .g paraffin or castrolite), thread, stop-watch, thermometer 0-100oC
E
E
C
D
A
heat
i.
HEAT CAPACITY OF METAL
METHOD
Fill the beaker B with some water, place the metal A inside it, and boil the water, meanwhile, weigh the calorimeter and
stirrer, fill it a bout one-half with tap water, and re-weigh. Take the temperature of the water in the calorimeter. Take
the temperature of the boiling water, and then quickly transfer metal A to the water in the calorimeter C. Observe the
water temperature every 10s until it reaches a maximum and then drops several degrees below the maximum reached.
MEASUREMENTS
Mass of calorimeter + stirrer m1 (c1 =… Jkg-1K-1)
=…kg
Mass of calorimeter + stirrer + water m1 + mass of A
=…kg
Initial water temperature t1
=…0C
Final temperature observed
=…0C
Final temperature, corrected for cooling t2
=…0C
Temperature of boiling water t
=…0C
COOLING CORRECTION
This may be obtained by a graphical method, as explained 0n p. 49. An alternative method is as follows: Suppose it took
a time x for the water to reach its final temperature when the hot metal was dropped in; then, approximately, the
cooling correction is the temperature drop from the maximum temperature in a time x/2. Since a metal is a good
conductor, it gives up its heat quickly, and the cooling correction may therefore be negligible.
CALCULATION
Heat lost by metal = Heat gained by water and calorimeter + stirrer. If C is the heat capacity of the metal and m the mass
of water of specific heat capacity
Cw(=4200Jkg-1K-1), then
CONCLUSION
The heat capacity of the metal was…JK-1
ERRORS
1. Heat lost by the hot metal on transferring it to the calorimeter;
2. Some hot water is carried over with the metal;
3. Observations of the temperature (e. g. 16.4+ 0.20c) and mass (e. g 194+ 194.6+ 0.1 x 10-3kg )
ORDER OF ACCURACY
ii.
SPECIFIC HEAT CAPACITY OF OIL
METHOD
Add some water to the beaker, place the metal A inside it, and heat the water until it boils. Meanwhile weigh the
calorimeter, fill it about one-half with the oil, and re-weigh. Observe the oil temperature. Take the temperature of the
boiling water, and then quickly transfer A to the oil. Observe the time taken for the oil to reach its maximum
temperature, and then find the temperature drop c, in half this time. This is the cooling correction
MEASUREMENTS
Mass of calorimeter m1+ stirer (c1 =…Jkg-1K-1)
=…kg
Mass of calorimeter + oil m1 + stirrer +Mass of A
=…kg
Initial oil temperature t1
=…0C
Final temperature, corrected for cooling t2
Temperature of boiling water t
Heat capacity of metal (C) ~ from previous experiment
=…0C
=…0C
=…JK-1
CALCULATION
Heat loss by metal = Heat gained by oil and calorimeter. If c is the oil’s specific heat capacity and m is the mass of the oil,
then with m and m1 in kg, calculate c from
H x (t-t1) = (mc + m1c1) (t2 – t1)
CONCLUSION
T he specific heat capacity of the oil was…Jkg-1K-1
ERRORS AND ORDER OF ACCURACY!