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RE ORGANISED BY ITUNE PHYSICS FOR BIOLOGIST SPH 2180 /SPH 2162(AERD/ AGRI/HORT/AFIM) A 2 FRICTION 1. COEFFICIENT OF DYNAMIC FRICTION Apparatus Wooden block A with a hook attached, a plane piece of wood B with a grooved wheel C at one end, scale-pan S, light string, weights, boxes of weights, spring balance. Method With the apparatus shown in Fig.8a, place a weight on S and give A a slight push towards C. Add increasing weights to S, giving A a slight push each time. At some stage, A will be found to continue moving with a steady, small velocity. Record the corresponding weight in the scale-pan S. Now increase the reaction of B by adding weights to A and repeat. Repeat for two more weights on A, returning the block to its original place in B each time. Measurements Weight of scale-pan = … N Weight of block A = … N Normal reaction, R/N Weight in scale-pan on moving A/N Frictional force, F’/N Calculation The frictional force, F’ = weight in scale-pan when A moves + weight of pan. Normal reaction, R = weight of A + other weights on A Graph Plot F’ v.R (Fig. 8c) The gradient, a/b = μ’= … Fig. 8c Conclusion The coefficient of dynamic friction is … Errors and order of accuracy As before. COEFFICIENT OF STATIC FRICTION F R a b B C S F R B C S F R
13

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Page 1: RE ORGANISED BY ITUNE PHYSICS FOR BIOLOGIST SPH …€¦ · RE ORGANISED BY ITUNE PHYSICS FOR BIOLOGIST SPH 2180 ... Apparatus Wooden block A with a hook ... (about 0.2kg) A, beaker

RE ORGANISED BY ITUNE

PHYSICS FOR BIOLOGIST SPH 2180

/SPH 2162(AERD/ AGRI/HORT/AFIM)

A2 FRICTION

1. COEFFICIENT OF DYNAMIC FRICTION

Apparatus

Wooden block A with a hook attached, a plane piece of wood B with a grooved wheel C at one end, scale-pan S, light string, weights, boxes of

weights, spring balance. Method

With the apparatus shown in Fig.8a, place a weight on S and give A a slight push towards C. Add increasing weights to S, giving A a slight push each time. At some

stage, A will be found to continue moving with a steady, small velocity. Record the corresponding weight in the scale-pan S. Now increase the reaction of B by adding weights to A and repeat. Repeat for two more weights on A, returning the block to its original place in B each time.

Measurements

Weight of scale-pan = … N

Weight of block A = … N

Normal reaction, R/N Weight in scale-pan on moving A/N Frictional force, F’/N

Calculation

The frictional force, F’ = weight in scale-pan when A moves + weight of pan. Normal reaction, R = weight of A + other weights on A

Graph

Plot F’ v.R (Fig. 8c) The gradient, a/b = μ’= …

Fig. 8c

Conclusion

The coefficient of dynamic friction is …

Errors and order of accuracy

As before.

COEFFICIENT OF STATIC FRICTION

F

R

a

b

B C

S

F

R

B C

S

F

R

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Apparatus

Wooden block A with a hook attached, a plane piece of wood B with a grooved wheel C at one end, scale-pan S, light string, weights, boxes of

weights, spring balance.

Method

Weigh the block A and the scale-pan S on the spring balance. Attach the scale-pan to the hook of A by light string passing round the wheel C. Mark

the position of A on the board B with pencil. Then gently add increasing weights to S until A just begins to slide. Record the total weight in S. Now

increase the reaction of B by placing a known weight on A and by adding increasing weights to S until A just begins to slide. Record the total weight

in S. Now increase the reaction of B by placing a known weight on A and by adding increasing weights to S again record the total weight in S when

A begins to slip. Repeat for two more increasing weights on A, returning the block A to its original place on B each time.

Measurements

Weight of scale-pan = …N

Weight of block A =… N

Normal reaction, R/N Weight in scale-pan on slipping /N Limiting frictional force, F/N

Calculation

The limiting frictional force, F = weight in scale-pan when A slips + weight of scale-pan.

Normal reaction, R = weight of A + other weights on A.

Graph

Plot F v.R (Fig.8b)

The gradient a/b = μ = …

Conclusion

The coefficient of static friction between block and plane at the place concerned is …

Errors and order of accuracy

Draw the lines with the least and greatest slopes, which just agree with the plotted

F

R

b

a

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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.

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?

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:

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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?

H19

Measurements of Specific Heat capacity of metals by Electrical

Method

Apparatus Metal (aluminium) block D with holes for immersion heater (heating coil) B and thermometer T (Griffin & George or Philip Harris); suitable supply S, voltmeter V, ammeter A, rheostat R; stopwatch.

Method 1. Insert the immersion heater B and thermometer T in the metal block (use a little glyseline to improve thermal contact between the thermometer bulb and the metal) (Fig 1)

2. Connect the electric circuit shown to the heater B. Use suitable high values of I and V.

3. Record the initial steady temperature on T. Then switch on the current, simultaneously start the stopwatch and record the temperature on T at equal intervals such as ½ min or 1 min for 30min.. During the

heating, keep the current and p.d. constant by means of the rheostat R.

4. After a suitable temperature rise has been obtained, switch off the current, and note the time t of heating. As the temperature of the metal continues to rise, record. Start cooling the metal blocks until the

temperature fall half of its maximum value reached.

a) Its final maximum temperature

b) The lower temperature reached 1 min later

5. Record the mass of the metal block. Repeat the experiment with values of V and I a little lower than before.

Measurements

Mass METAL = …kg

Temperature /oC

Time /s

Current I = …A

P.d. across coil V = …V

Initial water temperature =…oC

Maximum temperature = …oC

Calculation

Heat supplied = Ivt. The heat is in joule when I, V, t are in ampere, volt and second respectively.

Thus (Mc + mc1) θ = Ivt

Where m is the mass of oil of specific heat capacity c1, M is the mass of the calorimeter and stirrer, θ is the temperature rise (corrected for cooling), and t is the time for which the current was switched on. With m and M in

kg, calculate c.

Graph and cooling correction

Temp

Initial

temp.

Time

A2

A1

Max

D

T

R A

V S

C

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Plot a graph of temperature (oC) v. time (min). The ‘cooling correction’, r, is the temperature to be added to the final observed and can be calculate from the relation

r/A1 = x/A

2 or r = A

1/A

2 x

Where x is any temperature drop from the observed final temperature and A1, A

2 are the areas shown in Fig.15b. The areas A

1, A

2 are obtained by counting squares. From the graph.

r = A1/A

2 x = …K

Conclusion

The specific heat capacity of the oil was found to be …Jkg-1K-1.

Errors, order of accuracy

1. The masses may be determined to within 0.1% by weighing to the nearest tenth of a gram. No greater accuracy is required, as the other errors exceed this considerably.

2. The errors in the reading of the ammeter and voltmeter will depend upon the instruments used, and the size of their scales.

3. The error in the time is small, since the heating is fairly slow and t is large.

4. The error in θ is the sum of the error in measuring the initial and final temperatures and the cooling correction.

Neglecting the small percentage errors in t, M and m, the maximum percentage error in c1 is given approximately by:

δc1/c

1 X 100% = (δθ/θ + δI/I + δV/V) X 100%

Note a. The coil should have a resistance of about 5-6Ω, and should be well varnished.

b. The same method can be used to measure the specific heat capacity of water.

H18HEAT CAPACITY OF METAL

BLOCK & SPECIFIC HEAT CAPACITY OF

OIL i. HEAT CAPACITY OF A METAL BLOCK

ii. 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

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 m

1 (c

1 =… 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

heat

A

C

D

E

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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 (c

1 =…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 =…0C

Temperature of boiling water t =…0C

Heat capacity of metal (C) ~ from previous experiment =…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

)

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PHYSICS FOR BIOLOGIST II SPH 2181

REFRACTIVE INDEX- B9 AWS 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.

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 P1 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 P3 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

P

E B

C D

A

F

P1

P2

r

i

i

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B. APPARENT DEPTH METHOD

Apparatus

Glass or Perspex block B, traveling microscope M, lycopodium powder L and beaker

.

Method

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 r

1 (mm) r

2 (mm) r

3 (mm) (r

1-r

2) (mm) (r

1-r

3) (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:…………+ ….%.

(fig (a)). fig (b)).

r1

r2

r3

(fig (c)).

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C11: OHM’S LAW and Diode characteristics Objectives To verify or prove experimentally that these statements are true

a) Ohm’s law for a metallic conductor

b) R = R1

+ R2 + R

3 for resistances in series

c) 1/R = 1/R1 + 1/R

2 + 1/R

3 for resistances in parallel

d) Ohm’s law is not obeyed by a semiconductor

Apparatus

Theory Ohm’s law for a metal conductor states that potential difference, V, between two ends of the conductor is directly proportional to the current, I, flowing

through it, at a constant temperature. i.e. V = RI, where R is a constant known as resistance (in ohms)

Method A 1. Determine the resistances R

1, R

2 and R

3 separately as above.

2. Determine the resistances R1, R

2 and R

3 in series.

3. Determine the resistance of the three (R1

, R2 and R

3) resistors in parallel.

Record all values on the worksheet and test to see if the relationships for resistors in series and in parallel hold. Use your experimental values of V and I to

plot graphs of V versus I. A straight-line graph proves ohm/s law. Find Rs

from the slope of your graphs.

Method B Repeat the first part of the experiment using a semiconductor and draw the graph of V against I. Set the potentiometer R so that the voltage in V and the current

in A are zero. Adjust R so that voltage V increases in suitable small steps such as 0.2V from 0 to the maximum such as IV, and record the values of V and I from

the meters. Reverse the diode D in the circuit. Record the value of I at a reverse voltage of IV.

R1 R

2 R

3 Series Parallel

V (v) I (A) V (v) I (A) V (v) I (A) V (v) I (A) V (A) I (A)

From graphs From formula % Difference

R (series)

R (parallel)

Compare your experimental results with those obtained using the formula. Read the actual values of the resistors using the colour code and compare with

your experimental values. Discuss the sources of errors in these measurements on resistance. Is this the most accurate way of measuring resistance? If not,

what would you use and why? Comment on your graph. Is ohm’s law verified? Use a resistance meter to check your values for Rs. Comment

a) Semiconductor

Forward bias Reverse bias

(volts) I (amps) V (volts) I (amps)

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Calculation:Using the graph of forward bias (fig below), calculate:

1) The reciprocal, V/I, of the gradient of the graph at V=0.7v (this gives the a.c resistance of the diode at this voltage)

2) The ration V/I at V = 0.7, the D.C. resistance at this voltage.

a.c. resistance at 0.7v = … I

D.C. resistance at 0.7v =…

V I

O v

Use the chart below to determine the values of the resisances using the colour bands or codes.

color 1st – significant figure 2nd – significant figure 3rd - multiplier 4th - tolerance

Black 0 0 100 + 0%

Brown 1 1 101 + 1%

Red 2 2 102 + 2%

Orange 3 3 103 -

yellow 4 4 104 + 5%

Green 5 5 105 + 0.5%

Blue 6 6 106 + 0.25%

violet 7 7 107 + 0.1%

Grey 8 8 108 + 0.5% (+10%)

white 9 9 109 -

Gold - - 10-1 + 5%

Silver - - 10-2 +10%

None - - - +20%

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Use now the resistance meter to determine the actual values of the resistances.

Conclusion:

For comparison plot your six graphs on the same axis.

Discuss the resistance of the junction diode in forward and

reverse bias and whether the diode is an ‘ohmic’ or ‘non-

ohmic’ component.

Now write a independent lab report following all the step

B14TO VERIFY THE PROPERTIES OF LENSES

source of light object pin lens screen

Establish a rough value for converging mirror by focusing a distant object on the screen.

Switch on the illuminated object and place it a position greater than 2f from the mirror. Move the screen until

a clear image is in focus on it. Measure the distance from the object to the mirror (u) and from the mirror (v) .

Calculate f. Repeat u=2f, u>u<f, u=f and u<f

Fill in the table 3 below

Convex lens

Position

U

1/u

V

1/v

f

State of the image

Real/virtual Erect/inverted size

U>2f

U=2f

2f>u>f

U=f

U<f

Use the method of no parallax to locate the image in the convex mirror. Put it in the table 4 below.

Resistors Colour code Resistance meter

R1

R2

R3

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Concave lens.

Value units

u

v

f

1. Use the table for convex lens and draw a graph of 1/u versus 1/v and from the graph determine the focal

length of the convex lenses.

2. Use the lenses formula to determine the focal length of the concave lens

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.

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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.