A1PRECISION MEASUREMENTS- · 2016-09-13 · To study some of the instruments and methods used in...

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SPH 2160 PHYSCS I

A1PRECISION MEASUREMENTS- Objectives:

To study some of the instruments and methods used in precision measurements , and to compute the volume and density of various items.

Apparatus: Metre rule, vernier calipers ,micrometer screw gauge ,electronic balance and traveling microscope .Such items as copper cylinder , steel ball and glass

capillary tube are also supplied.

METHOD: The experiment comprises e measurement of the various objects supplied with the appropriate instruments. Where feasible, at least two instruments

should be used for each measurement and the precision obtained in each case compared. In this way, the volume and density of atleast two metal objects

weighings should be done on the electronic balance.In the second part of the experiment, some electrical circuits have been set up for you to measure the current.

Measure the current using an ammeter, a milliammeter and a microammeter, and estimate the reading errors in each case.N.B. in all cases an estimate of the

precision obtained should be, i.e. note the reading errors on all measurements. Where appropriate note the zero error.Record the data in work sheet 1,working out

any calculations asked for. Answer the questions posed on the sheet.

WORKSHEET 1

N.B. You must include in the table the units of any measurements you take.

ITEMS

MEASURING INSTRUMENTS

Meter

rule

Vernier

calipers

Micrometer

Screw Gauge

Balance

Ammete

r

Milli

Ammeter

µA

scope

Travelling Microscope

X Y Z

Zero error

Reading error

Copper cylinder:

mass

height

Diameter (external)

Diameter (internal)

Steel Ball: Diameter

Copper wire: length

Diameter

glass rod: diameter

length

Current

scope voltage signal

height peak-peak height

peak height=


Analysis :

volume Density of the material

Copper cylinder:

Internal volume

External volume

Steel bar

Glass rod

Calculation of voltage:

Instrument Value of Resistances Calculated V= IR

From Ammeter

From Milli-Ammeter

From µA

scope voltage signal sensitivity= voltage = sensitivity x height

ERRORS

Now work out the errors in volumes and densities and voltages calculated above using the reading errors of the appropriate instruments. Refer to the section on

errors in this manual for instructions on how to calculate errors.

volume Density of the material

Copper cylinder:

Internal volume

External volume

Steel bar

Glass rod

Instrument calculated V= IR

From Ammeter

From Milliammeter

From µA

from scope

QUESTIONS:Why is it appropriate to use the metre rule for measuring the length of the copper wire but the micrometer screw gauge for he diameter?.What

is the difference between accuracy and precision? CONCLUSION:The volume of the copper cylinder was found to be -----------------------------------------------------

(units) ,and its density was found to be------------------------ ------------------- ------------ (units)Write similar conclusions for the steel ball `and capillary tube ,

and give correct values for the densities of copper and steel . The values may be found in the reference book Tables of physical and chemical

constants,15th Edition , G.W.C. Kaye.and Labye (Longman 1986 ) .


A4Hookes 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: Weigh the spring using a balance. What would you expect the effective mass of the spring to be using this measured

vlue? Compare it with the one obtained from the graph.

Question 5:

What is the percent discrepancy between your value of g and the expected valu


FRICTION- A2 a) COEFFICIENT OF STATIC AND 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 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

B C

S

F

R


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 points. Find the error in μ from the

variation in slope.

b) COEFFICIENT OF DYNAMIC FRICTION

Apparatus As before

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

F

R

b

a


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’= …

Conclusion

The coefficient of dynamic friction is …

Errors and order of accuracy As before.

F

R

a

b


H19Measurements 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

D

T

R A

V S

C


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

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/A2 or r = A1/A2 x

Where x is any temperature drop from the observed final temperature and A1, A2 are the areas shown in Fig.15b. The areas A1, A2 are obtained by

counting squares. From the graph.

r = A1/A2 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/c1 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.

Temp

Initial

temp.

Time

A2 A

Max


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 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

heat

A

C

D

E


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 =…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)


CONCLUSION T he specific heat capacity of the oil was…Jkg-1K-1

ERRORS AND ORDER OF ACCURACY!

Sph 2161 phyics 11

B7: PROPERTIES OF LENSES OBJECTIVESs

1. To investigate properties of lenses.

PROPERTIES OF LENSES:

Apparatus

An illuminated object, pins, screen, concave and convex lenses.

Fig.2

Theory

The location and type of image formed in a lens can beascertained by drawing a ray diagram:

The ray of light from the object, which enters the lens parallel to the principle axis, will be refracted through

the focus.

The ray of light, which goes through the center of the lens, will emerge undeviated.

It can be shown that: 1=1+1

f u v

Where f=focal length.

u=distance of object from the lens.

v=distance of image from the lens.

Method:

1. Establish a rough value for the focal length of the convex lens by focusing on a distant object (e.g. window

of laboratory) on the screen.

lens

Lens holder

screen

Illuminated

object


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

until a clear image is in focus on it.

3. Measure the distance from the object to the lens (u) and from the lens to the screen (v).

4. Calculate f using the above values of u and v.

5. Repeat the above steps for following positions of the object: u=2f; 2f<u<f; u=f. Get 1/u and 1/v of each data

obtained and draw graph of 1/u versus 1/v. From the graph determine the focal lenth of the lense.

6. Using the lense formulae, determine the focal length of each step and finaly the average value of f. compare

with the one obtained using the the graphical method

1=1+1

f u v

NB: hand in original ray diagrams

7. Use the method of parallax to determine the focal length of diverging lens using the object pin and

the long search pin provided. No source light is required.

8. Repeat this 3 times and write it down in a suitable table.

9. Calculate the average value of the focal length of the diverging lens.

Lenses:

i) Convex lens

u v u-1 v-1 calculated f State if the image is:

Error &

units Real/virtual Upright/in

verted

Magnified/di

minished

u>2f

U=2f

F<u<2f

U=f

U<f

Average f?

Conclusion.

n for glass was found to be ……………+ ….. %. Focal length of converging lens was 1. Rough

value………+ ….. %. 2. From average………………………+ ….. %. 3. From graphical

method……………….. + ….. %.


C12- WHEATSTONE BRIDGE Aim: to find the values of resistances

X1 , X2 and X3

To find out whether the formulas of 1. Resistances in series 2. And parallel are true.

To find the resistivity of the material of the wire given

Theory

When resistances are connected as shown in Fig. 2 below, they constitute a wheatstone network. If P, Q and R are known

resistances adjusted in such away that the galvanometer G reads zero, the points B and D will be at the same potential and no

current flows between them. The network is said to be balanced. Thus:If the current through the meter is Ig = 0 , I1 =I3 and I2=I4.Or

I2/I1=I4/I3 also PI1/RI2 =QI3 =XI4. Hence X = QR/P. If the above condition is satisfied then it is possible to use the network to determine

the value of the unknown resistance X

Apparatus: Decade resistance box, wheat stone bridge, dry cell, three assorted resistors, galvanometer, resistivity wire,

galvanometer and assorted wires.

Procedure/method: In Fig. below , P and Q are resistances of the portions AB and BC respectively, of a wire of uniform

resistance. Commonly, this wire is 50 or 100 cm long. The point B on the wire is where the galvanometer G shows no

deflection. P and Q will be proportional to the lengths AB and BC of the wire, respectively. R is a standard resistance (decade

resistance box). Set up the circuit as shown in Fig. 1 above. Find an approximate balance point with the protective resistor in the circuit

(NB: this resistor limits current flowing in the galvanometer). Now obtain the accurate balance point by shorting this protective resistor.

Reverse the terminals of the accumulator E and repeat the measurement. Interchange R and X, and repeat the procedure. How does the

balance point change? Repeat the experiment for two other resistors X and tabulate your results with errors.Measure the resistances of

the unknown resistor X and compare the values with those from your experiment.

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%

Part 2: Resistivity of the wire

Now use the bridge to measure the resistance of each of the wire given. Before connecting the battery to the

bridge, carefully check that all the connections are correct. Get the wire, attach it to the bridge, and set the

decade box resistance Rk to be as near to Rx as possible(you know Rx roughly from your DMM measurements).

Balance the bridge by moving the sliding contact along the wire while watching the galvanometer. With the

bridge balanced, measure L1 and L2, and compute

(11) .

Repeat this procedure as the table below shows.

From the results from the table , compute the average resistivity, and the uncertainty of the average ( ).

Compare your average value with the known value.

Ig

I1 I3

I4 I2


Now use the resistance meter to determine the actual values of the resistances.

TABLE OF RESULTS :

LENGTHS DUE TO TERMINALS UNREVERSED TERMINALS REVERSED Actual resistance (meter)

P Q P Q

X1

X2

X3

X1 and X2 series

X1 and X3 series

X2 and X3 series

X1 , X2and X3 series

X1 and X2 parallel

X2and X3parallel

X1 and X3parallel

X1 , X2and X3parallel

Wire given length= ...………cm

Diameter= …………. mm

AFTER INTERCHANGING R AND X:

LENGTHS DUE TO TERMINALS UNREVERSED TERMINALS REVERSED Actual resistance (meter)

P Q P Q

X1

X2

X3

X1 and X2 series

X1 and X3 series

X2 and X3 series

X1 , X2and X3 series

X1 and X2 parallel

X2and X3parallel

X1 and X3parallel

X1 , X2and X3parallel

Wire given length= ...………cm Diameter= …………. mm

Questions: How would the resistance per unit length change if you used: A) a shorter wire B)a thicker wire, than that

used in Q. 2 above.What are the possible sources of error in the experiment?


B13 LAWS OF REFRACTION Aim: 1. Determination of refractive index of glass by

plotting (graphical method)

apparent depth method

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 line 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 precicely.

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.

P

E B

C D

A

F

P1

P2

r

i

i


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.

r3

m v r1 m m v r2 m

a) b) } a c)

p p p

Method

Place the block B on a sheet of paper P and arrange the traveling microscope so that the microscope M and the scale s are vertical.

Focus the microscope M on the upper surface of the block using a little lycopodium powder L or chalk dust if necessary (Fig.1

(a)). Having achieved a sharp focus using the fine adjustment screw take the reading r1 of the vernier v on the scale S.

Move the microscope down until the paper seen through the block is in sharp focus. Take the reading r2 of the vernier (fig 1 (b)).

Remove the block and focus on the paper and take the vernier reading r3 (Fig.3 (c)). Turn the block onto another face and repeat

the measurements.

Calculate (r1-r2) (mm) /(r1-r3) (mm) to get n. repeat this 5 more times

Measurements

r1 (mm) r2 (mm) r3 (mm) (r1-r2) (mm) (r1-r3) (mm) (r1-r2) (mm) /(r1-r3) (mm)= n

AVERAGE VALUE OF n


Now draw a graph of (r1-r2) (mm) /(r1-r3) (mm) and find n graphically.

The refractive index of glass was found to be:

Plotting method:…………+ ….% Apparent 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.

A1PRECISION MEASUREMENTS- · 2016-09-13 · To study some of the instruments and methods used in...

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Transcript of A1PRECISION MEASUREMENTS- · 2016-09-13 · To study some of the instruments and methods used in...