Government College University, Faisalabad Department of Telecommunication Engineering,

Applied Physics

Lab Manual

document.doc 2

Prepared & Edited by:

Dr. Ijaz Ahmad Khan (Assistant Professor)

Engr. Maria Hanif (Lab Engineer)

Verified by:

Engr. Kasif Nisar Paracha (Lecturer)

Approved by:

Engr. Muhammad Afzal Sipra (TI, M)

Associate Professor and Chairman

Telecommunication Engineering Department

document.doc 3

TABLE OF LAB EXPERIMENTS

Sr. No. Experiment Page No.

1.To analyze simple circuits using Ohm’s Law.

6

2.To determine the frequency of AC supply.

10

3. To use potentiometer as a voltage divider. 13

4. To demonstrate current flow in rectifier circuits by using LED’s. 16

5.To study the characteristics of RLC series (acceptor) circuit.

21

6.To study the characteristics of RLC parallel (rejecter) circuit.

25

7.To observe voltage distribution in capacitive circuits and explore series and parallel combinations of capacitors.

29

8.To study differentiator & integrator circuits.

33

9.To use LDR in circuit design. 40

10.To determine the value of an unknown small resistance using a Carey Foster’s bridge. 44

11.To determine the height of inaccessible object.

48

12 Semester Project51

document.doc 4

PREFACE

The purpose of the science of Physics is to explain natural phenomena. It is the laboratory where

new discoveries are being made. This is where the physicist is making observations for the

purpose of identifying the patterns which may later be fit to mathematical equations. Theories

are constructed to describe patterns observed and are tested by further experimentation.

The laboratory of each and every subject taught in the degree of Bachelors in Electrical

Engineering is of very much importance in every University. Fully equipped laboratories

meeting the industrial demands under the supervision of qualified, talented and practically

motivated lab assistants and lab engineers is also a basic criterion of the Pakistan Engineering

Council. This Manual has been formulated considering all these above mentioned points.

This manual is according to the equipment supplied by the RIMS, USA and meets the

requirements of all the course of Applied Physics as per the curriculum of G. C. University

Faisalabad.

With Regards

Engr. Maria Hanif

document.doc 5

General Lab Instructions

Each student group consists of a maximum of 2-4 students. Each group member is responsible in submitting lab report upon completion of each experiment on their practical Note book.

Students are to wear proper attire i.e. shoe or sandal instead of slipper. Excessive jewelleries are not advisable as they might cause electrical shock.

A permanent record in ink of observations as well as results should be maintained by each student and enclosed with the report.

The recorded data and observations from the lab manual need to be approved and signed by the lab instructor upon completion of each experiment.

Before beginning connecting up, it is essential to check that all sources of supply at the bench are switched off.

Start connecting up the experiment circuit by wiring up the main circuit path, then adds the parallel branches as indicated in the circuit diagram.

After the circuit has been connected correctly, remove all unused leads from the experiment area, set the voltage supplies at the minimum value, and check the meters are set for the intended mode of operation.

The students may ask the lab instructor to check the correctness of their circuit before switching on.

When the experiment has been satisfactory completed and the results approved by the instructor, the students may disconnect the circuit and return the components and instruments to the locker tidily. Chairs are to be slid in properly.

document.doc 6

Experiment No. 1

OHM’S LAWOBJECTIVE

In this lab you will learn how to analyze simple circuits using Ohm’s Law

EQUIPMENT: Digital Multimeter (DMM)

Resistors:

E-PAL (Training board)

THEORY:Ohm's law states that the current through a conductor is directly proportional to the potential difference across the ends of the conductor. Mathematically

V = IR

where I is the current (amperes), V is the potential difference (volts) and R is the resistance of the conductor (ohms). If, R is constant than there is a linear relation between V and I.

Fig.1: Ohm’s law

The law was named after the German physicist Georg Ohm. The slope of a V(I) graph is R. This relationship can be checked by measuring the current through and voltage across each resistor.

When measuring current be sure to place the ammeter in series with the components in question. Current flows through a circuit. When measuring voltage be sure to place the voltmeter in parallel with the resistance. Voltage drops across a resistor.

No doubt you noticed in the DC Circuits lab that voltages recorded across the series components very nearly summed to the power supply voltage. And it's almost certain that you discovered that

document.doc 7

voltage measured across each component in the parallel configuration was quite close to the power supply setting. Therefore, your astute observations should help you with this experiment as well.

CIRCUIT DIAGRAM:

Fig.2 Resisters in series

Fig.3 Resister in parallel combination

Procedure:

1. Connect the circuit according to circuit diagram of Figure 2.

2. Let R1 = 180 Ohms, R2 = 220 Ohms, R3 = 330 Ohms

3. Set the power supply to 12 volts.

4. Measure the current (in milliamps) through and voltage drop (in volts) across each resistor.

5. Connect the circuit according to circuit diagram of Figure 3.

6. Let R1 = 180 Ohms, R2 = 220 Ohms, R3 = 330 Ohms.

document.doc 8

7. Set the power supply to 3 volts.

8. Measure the current (in milliamps) through and voltage drop (in volts) across each resistor.

9. Also measure the current between the + side of the battery or power supply and R1.

CALCULATIONS:

For circuit # 1 (series):

1. Calculate the total resistance.

2. Calculate the theoretical current (in Amps) value using the total resistance value and the value of the input voltage.

3. Calculate the theoretical value of the voltage drop across each resistor by using the theoretical current value.

4. Calculate the percent error for the current (use the average of your measured values (in Amps) as your experimental value).

5. Calculate the percent error for the voltage drops across each resistor.

For Circuit # 2 (parallel):

1. Calculate the total resistance.

2. Calculate the theoretical value of the total current (in Amps) by using the total resistance and the value of the input voltage.

3. Calculate the theoretical value of the current (in Amps) through each resistor. You may assume that the voltage across each resistor is the same as the input voltage.

document.doc 9

4. Calculate the percent error for the total current.

5. Calculate the percent error for the values of the currents through each resistor.

RESULTS & CALCULATIONS:For circuit # 1:

RT (calculated) = ___________,

I(calculated) using calculated value of RT and input voltage V= ___________

VR1 (calculated) = ___________, VR2(calculated) = ___________

VR3 (calculated) = ___________

For circuit # 2:

RT (calculated) = ___________,

I(calculated) using calculated value of RT and input voltage V= ___________

IR1 (calculated) = ___________, IR2(calculated) = ___________

IR3 (calculated) = ___________

DISCUSSION AND CONCLUSION:1) -------------------------------------------------------------------------------------------

2) -------------------------------------------------------------------------------------------

3) --------------------------------------------------------------------------------------------

document.doc 10

Experiment No. 2

MELDE’S EXPERIMENTOBJECTIVE:

In this lab you will learn how to determine the frequency of AC supply.

EQUIPMENT: A stand with clamp and pulley  

A light weight pan  

A weight box

  Balance 

 A battery with eliminator and connecting wires  

Fig.1 Melde's experiment

document.doc 11

THEORY: “ An experiment to study transverse vibrations in a long, horizontal thread when one end of the thread is attached to a point of a vibrator , while the other passes over a pulley and has weights suspended from it to control the tension in the thread. “Melde's experiment is a scientific experiment carried out by the German physicist Franz Melde on the standing waves produced in a tense cable originally set oscillating by a tuning fork, later improved with connection to an electric vibrator. This experiment attempted to demonstrate that mechanical waves undergo interference phenomena. In the experiment, mechanical waves traveled in opposite directions from immobile points, called nodes. These waves were called standing waves by Melde since the position of the nodes and loops (points where the cord vibrated) stayed static.

Transverse wave motion: A transverse wave motion is that wave motion, in which individual particles of the medium execute simple harmonic motion about their mean position in a direction perpendicular to the direction of propagation of wave motion.

Fig.2 Transverse wave

Tension:In physics, tension is (magnitude of) the pulling force exerted by a string, cable, chain, or

similar solid object on another object.

PROCEDURE:1) Find the weight of pan and mass of thread 1cm in length.

2) Set the apparatus according to figure.

3) Excide the steel strip by passing A.C. current through the coil of electromagnet and put a

document.doc 12

small weight in the scale pan. The thread will vibrates under the forced vibration of steel strip.

4) Take the readings according to table and calculate the frequency by using this formula:

n=1/2l(√T/m)

5) Increase the weights in pan and calculate the frequency again.

Fig.3 Block diagram of melde’s experiment

RESULTS & CALCULATIONS:Table 1

No. of Obs.

Mass of weight in pan

No. of loops

p

Distance between extreme

nodes L

Length of each

loop l=L/p

Mass of the

pan+ wts.

Added to it W

Tension in dynes

T=Wx981n=1/2l√(T/m)

gms cms. cms. gms dynes vib./sec.1 2 3 4

document.doc 13

DISCUSSION AND CONCLUSION:1. -------------------------------------------------------------------------------------------

2. -------------------------------------------------------------------------------------------

3. --------------------------------------------------------------------------------------------

Experiment No.3

TO STUDY POTENTIAL DIVIDER CIRCUITOBJECTIVE:

In this lab you will learn how to use potentiometer as a voltage divider.

EQUIPMENT / COMPONENTS REQUIRED:

DMM TRAINER BOARD Resistor

Variable resistor

LAB SAFETY CONCERNS:

Make sure all circuit connections are correct, and no shorted wires exist. Adjust the power supply to the proper voltage before connecting it to the circuit Adjust signal generator to the proper level before connecting it to the circuit When using electrolytic capacitors, the arrows must point to the negative side of current

flow.

THEORY:

A potentiometer is a manually adjustable electrical resistor that uses three terminals. In many electrical devices, potentiometers are what establish the levels of output. For example, in a loudspeaker, a potentiometer is used to adjust the volume. In a television set, computer monitor or light dimmer, it can be used to control the brightness of the screen or light bulb.

document.doc 14

Fig.1 Potentiometer

Fig.2 Circuit diagram of potentiometer

Working:Potentiometers, sometimes called pots, are relatively simple devices. One terminal of the potentiometer is connected to a power source, and another is hooked up to a ground — a point with no voltage or resistance and which serves as a neutral reference point. The third terminal slides across a strip of resistive material. This resistive strip generally has a low resistance at one end, and its resistance gradually increases to a maximum resistance at the other end. The third terminal serves as the connection between the power source and ground, and it usually is operated by the user through the use of a knob or lever.The user can adjust the position of the third terminal along the resistive strip to manually increase or decrease resistance. The amount of resistance determines how much current flows through a circuit. When used to regulate current, the potentiometer is limited by the maximum resistivity of the strip.

document.doc 15

Fig.3 Circuitry of variable resistor

PROCEDURE: Construct the circuit given in figure below

Fig.4Circuit diagram

CALCULATIONS

1) Calculate & Measure the value of Vout.

2) What happens if 9k is replaced by 1k?

3) What happens if 9k is replaced with 2k?

4) What happens if 1k is replaced with zero?

5) .Replace +12V with ground. Measure Vout and answer all of the above questions.

CONCLUSION: 1. ---------------------------------------------------------------------------------------------------

2. ---------------------------------------------------------------------------------------------------

document.doc 16

3. ---------------------------------------------------------------------------------------------------

document.doc 17

Experiment No. 4

RECTIFIER CIRCUIT

OBJECTIVE:

To demonstrate current flow in Rectifier Circuits by using LED’s

EQUIPMENT / COMPONENTS REQUIRED:

DMM Trainer Board Resistor Diode

THEORY:

Half-Wave RectifiersAn easy way to convert ac to pulsating dc is, to simply allow half of the ac cycle to pass, while blocking current to prevent it from flowing during the other half cycle. The figure below shows the resulting output. Such circuits are known as half-wave rectifiers because they only work on half of the incoming ac wave. 

Fig.1 Half Wave Rectifier

Fig.2 Output of Half wave rectifier

document.doc 18

Full-Wave RectifiersThe more common approach is to manipulate the incoming ac wave so that both halves are used to cause output current to flow in the same direction. The resulting waveform is shown below. Because these circuits operate on the entire incoming ac wave, they are known as full-wave rectifiers.

Fig.3 Full-Wave Rectifier

Fig.4 output of Full wave rectifier

PROCEDURE: For half wave rectification

Construct the circuit given in figure below. Observe the output using oscilloscope.

Make the following measurements and take the snap short of output signal..

document.doc 19

Fig.5 Circuit Diagram

CALCULATIONS

Table 1

GRAPH

document.doc 20

Sr. no. Input Output

(Vrms) (V)

1 20

2 30

For full-wave rectification Construct the circuit given in figure below.

Fig.6 Circuit Diagram

Observe the out put using oscilloscope. Make the following measurements and take the snap short of out put signal.

Table 2

Sr. no. In put Out put

Vrms V

1 20

2 30 GRAPH

document.doc 21

CONCLUSION:1. ------------------------------------------------------------------------------------------------------------

2. ------------------------------------------------------------------------------------------------------------

3. ------------------------------------------------------------------------------------------------------------

document.doc 22

Experiment No. 5

ACCEPTOR CIRCUITS

OBJECTIVE: To study the characteristics of RLC series (acceptor) circuit

EQUIPMENT / COMPONENTS REQUIRED:

Audio oscillator

Resistors (100-1000 ohm)

Capacitors (0.1µf)

Inductance (500mH)

DMM

THEORY:A given combination of R, L and C in series allows the current to flow in certain frequency ranges only. For this reason it is known as an acceptor circuit i.e., it accepts some specific frequencies.

A series-resonant circuit that has a low impedance at the frequency to which it is tuned and a higher impedance at all other frequencies

At resonance frequency, XC=XL and XL-XC = 0. Therefore, the only electrical characteristic left in the circuit to oppose current is the internal resistance of the two components and resistance used. Hence, at resonance frequency, Z = R.

Fig.1 Acceptor Circuit

document.doc 23

RESONANCE:For a certain frequency of the sinusoidal voltage applied to RLC series circuit the current flowing in the circuit has a maximum value. This phenomenon is called resonance.

RESPONSE CURVE:When RLC series circuit is excited by a sinusoidal voltage, the current changes with frequency of applied voltage. A graph between current n frequencies is known as the response curve.

Fig.2 Response curve

QUALITY FECTOR:It is the ratio between the resonance frequency and the bandwidth, i.e.

Quality factor=Q= fr/∆fPROCEDURE:

Construct the circuit given in figure below.

Fig.3 Circuit diagram

document.doc 24

Set the oscillator to resonance frequency.

Switch on the oscillator and observe the current flowing in the circuit with the help of multi-meter.

Observe the current by increasing and decreasing the frequency and note the corresponding current.

Record two more sets of observations for different values of R.

GRAPH:

document.doc 25

CALCULATIONS:

fr=………hertz

R ohms No. of Obs. 1 2 3 4 5 6 7 8 9

R1=

freq. (Hz) Current (mA)

R2=

freq. (Hz) Current (mA)

R3=

freq. (Hz) Current (mA)

Results from graph: Lower limit frequency= f1 =………….hz

Upper limit frequency= f2 =………….hz

Bandwidth = f2 – f1=∆f=……hz

Quality factor =Q=fr/∆f=………

DISCUSSION AND CONCLUSION:1) -------------------------------------------------------------------------------------------

2) -------------------------------------------------------------------------------------------

3) -------------------------------------------------------------------------------------------

document.doc 26

Experiment No. 6

REJECTER CIRCUITS

OBJECTIVE: To study the characteristics of RLC parallel (rejecter) circuit

EQUIPMENT / COMPONENTS REQUIRED:

Audio oscillator

Resistors (100-1000 ohm)

Capacitors (0.1µf)

Inductance (500mH)

DMM

THEORY:A given combination of R, L and C in parallel dis-allows the current to flow in certain frequency ranges only. For this reason it is known as a rejecter circuit i.e., it rejects some specific frequencies.

A parallel-resonant circuit that has a high impedance at the frequency to which it is tuned and a low impedance at all other frequencies

At resonance the impedance of the capacitor becomes equal to that of inductor (XC=XL) hence impedance is maximum so no current flows. At low frequency the capacitive reactance is high so all current flows through inductor and when the frequency is high all current flows through capacitor because at that point reactance of the capacitor is low. So we obtained a V shape graph.

It’s also used in radio stations where we have to reject current for certain frequency range.

Zeq = (1/ZL) + (1/ZC) + (1/ZR)

document.doc 27

Fig.1 Circuit diagram

RESONANCE:For a certain frequency of the sinusoidal voltage applied to RLC parallel circuit the current flowing in the circuit has a minimum value. This phenomenon is called resonance.

RESPONSE CURVE:When RLC parallel circuit is excited by a sinusoidal voltage, the current changes with frequency of applied voltage. A graph between current n frequency is known as the response curve.

Fig.2 Response Curve

document.doc 28

QUALITY FACTOR:It is the ratio between the resonance frequency and the bandwidth, i.e.

Quality factor=Q= fr/∆fPROCEDURE:

Construct the circuit given in figure below.

Set the oscillator to resonance frequency.

Switch on the oscillator and observe the current flowing in the circuit with the help of multimeter.

Observe the current by increasing and decreasing the frequency and note the corresponding current.

Record two more sets of observations for different values of R.

Fig.3 Circuit diagram

GRAPH:

document.doc 29

CALCULATIONS:

fr=………hertz

Table 1

R ohms No. of Obs. 1 2 3 4 5 6 7 8 9

R1=

freq. (Hz) Current (mA)

R2=

freq. (Hz) Current (mA)

R3=

freq. (Hz) Current (mA)

Results from graph Lower limit frequency= f1 =………….hz

Upper limit frequency= f2 =………….hz

Bandwidth = f2 – f1=∆f=……hz

Quality factor =Q=fr/∆f=………

DISCUSSION AND CONCLUSION:

1) -------------------------------------------------------------------------------------------

2) -------------------------------------------------------------------------------------------

3) --------------------------------------------------------------------------------------------

document.doc 30

Experiment No. 7

STUDY OF CAPACITORS

OBJECTIVE: In this experiment we will determine how voltages are distributed in capacitor circuits

and explore series and parallel combinations of capacitors.

EQUIPMENT: DMM Trainer board Capacitors of different values

THEORY:The capacitance is a measure of a device’s ability to store charge. Capacitors are passive electronic devices which have fixed values of capacitance and negligible resistance. The capacitance, C, is the charge stored in the device, Q, divided by the voltage difference across the device, ∆V:

C = Q/∆V. (1)

The SI unit of capacitance is the farad, 1 F = 1 C/V, In general, the capacitance can be calculated knowing the geometry of the device. For most practical devices, the capacitor consists of capacitor plates which are thin sheets of metal separated by a dielectric, insulating material. For this reason, the schematic symbol of a capacitor is has two vertical lines a small distance apart (representing the capacitor plates) connected to two lines representing the connecting wires (or leads).

There are two ways to connect capacitors in an electronic circuit - series or parallel connection.

SERIES:

document.doc 31

In a series connection the components are connected at a single point, end to end as shown below:

Fig.1 Capacitor in series

For a series connection, the charge on each capacitor will be the same and the voltage drops will add. We can find the equivalent capacitance, Ceq, from

Q · 1/Ceq = ∆V = ∆V1 + ∆V2 = Q/C1 + Q/C2 = Q [1/C1 + 1/C2] (3)So

1/Ceq = 1/C1 + 1/C2 (4)PARALLEL: In the parallel connection, the components are connected together at both ends as shown below:

Fig.2 Capacitor in parallel

For a parallel connection, the voltage drops will be the same, but the charges will add. Then the equivalent capacitance can be calculated by adding the charges:

Ceq∆V = Q = Q1 + Q2 = C1∆V + C2∆V = [C1 + C2] ∆V (5)So

Ceq =C1 + C2 (6)NOTE: Here we will use AC, the voltage is actually ∆V = I/ωC, where I is the current and ωis the angular frequency. We don’t actually measure I or ω here, and the analysis is the same .

document.doc 32

PROCEDURE:From the Diagram below, perform the following steps as mentioned under the diagram.

CIRCUIT DIAGRAM:

Fig.3 Circuit diagram

1. Turn on the power supply and set the AC voltage to 10 V.Measure the accurate voltage with the multimeter and record it below:Vac = ___________________V

2. Connect two 0.1 µF capacitors in series. Measure V2 (across C2) and record it below.V2 (measured) = ____________ V

3. Compute the expected value of V2 using Vac, the values of C1 and C2 with equations 3 and 4.V2 (expected) = ____________ V% difference = |measured - expected| / measured x 100 % =__________

4. Connect a third 0.1uF capacitor in parallel with C2.Compute their equivalent capacitance.Ceq = _________ µF.

Measure and compute the voltage across the equivalent capacitance.

Veq (measured) = ___________ V, Veq (expected) = _________V,

% difference = __________

5. Now remove the third capacitor and replace it with a 0.01uF capacitor.Compute their equivalent capacitance.Ceq = _________ µF.

document.doc 33

Measure and compute the voltage across the equivalent capacitance.Veq (measured) = ___________ V, Veq (expected) = _________V, % difference = __________

6. Now connect the 0.1uF and the 0.01uF capacitor in series. Compute the equivalent capacitance.Ceq = _________µF.

Measure and compute the voltage across the equivalent capacitance.Veq (measured) = ___________ V, Veq (expected) = _________V, % difference = __________

7. This method can be used to find an unknown capacitance. Replace C1 with the unknown value capacitor and determine its capacitance by measuring V2 and using equations 3 and 4.V1 = ___________ V, C1 = _________ uF.

DISCUSSION AND CONCLUSION:1) -------------------------------------------------------------------------------------------

2) -------------------------------------------------------------------------------------------

3) --------------------------------------------------------------------------------------------

document.doc 34

Experiment No. 8

STUDY OF RC WAVEFORMS

OBJECTIVE: To study differentiator & integrator circuits

EQUIPMENT: DMM TRAINER BOARD Resistor Oscilloscope

THEORY:

Square Wave Signal:

If we apply a Square Wave voltage to the RC circuit whose frequency matches that exactly of the 5RC time constant of the circuit, then the voltage waveform across the capacitor would look something like this:

Fig.1 5RC Input Waveform:

The voltage drop across the capacitor alternates between charging up to Vc and discharging down to zero according to the input voltage. Here in this example, the frequency (and therefore the time period, ƒ=1/T) of the input square wave voltage exactly matches that of the RC time constant, ƒ=1/RC, and the capacitor is allowed to fully charge and fully discharge on every cycle resulting in a perfectly matched RC waveform.If the time period of the input waveform is made longer (lower frequency, ƒ<1/RC) for example a time period equivalent to say "8RC", the capacitor would then stay fully charged longer and

document.doc 35

also stay fully discharged longer. As shown in fig.2. If however we reduced the time period of the input waveform (higher frequency, ƒ>1/RC), to "4RC" the capacitor would not have sufficient time to either fully charge or discharge and the resultant voltage drop across the capacitor, Vc will be less than its maximum input voltage as shown below in fig.3.

Fig.2 An 8RC Input Waveform:

Fig.3 A 4RC Input Waveform

document.doc 36

Frequency Responses

The Integrator

The Integrator is a type of Low Pass Filter circuit that converts a square wave input signal into a triangular waveform output. As seen above, if the RC time constant is long compared to the time period of the input RC waveform the resultant output will be triangular in shape and the higher the input frequency the lower will be the output amplitude compared to that of the input. Consider the output across the capacitor at high frequency i.e.

This means that the capacitor has insufficient time to charge up and so its voltage is very small. Thus the input voltage approximately equals the voltage across the resistor.

Fig.4 Circuit diagram

By ohm’s law

So

Thus output is the integral of input voltage.

The Differentiator

The Differentiator is a High Pass Filter type circuit that converts a square wave input signal into high frequency spikes at its output. If the RC time constant is short compared to the time period of the input waveform the capacitor will become fully charged quickly before the next change in the cycle. When the capacitor is fully charged the output voltage across the resistor is zero. The arrival of the falling edge of the input waveform causes the capacitor to reverse charge giving a

document.doc 37

negative output spike, then as the square wave input changes during each cycle the output spike changes from a positive value to a negative value.

Fig.5 Circuit diagram

Consider the output across the resistor at low frequency i.e.,

This means that the capacitor has time to charge up until its voltage is almost equal to the source's voltage.

Thus the output voltage is the derivative of input voltage.

Cut-off Frequency

In physics and electrical engineering, a cutoff frequency, corner frequency, or break frequency is a boundary in a system's frequency response at which energy flowing through the system begins to be reduced (attenuated or reflected) rather than passing through.

fc=1/2πRCWhere RC is the time constant of the circuit previously defined and can be replaced by tau, T. This is another example of how the Time Domain and the Frequency Domain concepts are related.

PROCEDURE:

1. Draw the circuits of Differentiator & Integrator and verify the information provided above in the discussion.

2. Do your waveforms match those that are provided in the figures above, Explain any differences.

document.doc 38

GRAPH OF THE OUTPUT OF INTEGRATOR CIRCUIT

document.doc 39

GRAPH OF THE OUTPUT OF DIFFRENTIATOR CIRCUIT

document.doc 40

DISCUSSION AND CONCLUSION

1) -------------------------------------------------------------------------------------------

2) -------------------------------------------------------------------------------------------

3) --------------------------------------------------------------------------------------------

LIGHT DEPENDENT RESISTOR (LDR) LIGHT DEPENDENT RESISTOR (LDR)

document.doc 41

Experiment No. 9

LIGHT LIGHT DEPENDENT RESISTOR (LDR)

OBJECTIVE:

In this lab you will learn how to use LDR in Circuit design

EQUIPMENT / COMPONENTS REQUIRED:

DMM TRAINER BOARD Resistor LDR

THEORY:

A photo resistor or light dependent resistor is a component that is sensitive to light. When light falls upon it then the resistance changes. Values of the resistance of the LDR may change over many orders of magnitude the value of the resistance falling as the level of light increases.It is not uncommon for the values of resistance of an LDR or photo resistor to be several mega ohms in darkness and then to fall to a few hundred ohms in bright light. With such a wide variation in resistance, LDRs are easy to use and there are many LDR circuits available.LDRs are made from semiconductor materials to enable them to have their light sensitive properties. Many materials can be used, but one popular material for these photo resistors is cadmium sulphide (CdS).

Fig.1 LDR

document.doc 42

How an LDR works

It is relatively easy to understand the basics of how an LDR works without delving into complicated explanations. It is first necessary to understand that an electrical current consists of the movement of electrons within a material. Good conductors have a large number of free electrons that can drift in a given direction under the action of a potential difference. Insulators with a high resistance have very few free electrons, and therefore it is hard to make them move and hence a current to flow.An LDR or photo resistor is made any semiconductor material with a high resistance. It has a high resistance because there are very few electrons that are free and able to move - the vast majority of the electrons are locked into the crystal lattice and unable to move. Therefore in this state there is a high LDR resistance.

As light falls on the semiconductor, the light photons are absorbed by the semiconductor lattice and some of their energy is transferred to the electrons. This gives some of them sufficient energy to break free from the crystal lattice so that they can then conduct electricity. This results

in a lowering of the resistance of the semiconductor and hence the overall LDR resistance.

The process is progressive, and as more light shines on the LDR semiconductor, so more electrons are released to conduct electricity and the resistance falls further.

PROCEDURE:

1. Construct the circuit according to fig1.

2. Start with, using a 100   resistor as the test resistor. 3. Make measurements of Vout first with the LDR in the light and then with the LDR in

the shade. Write these results in the table below:

Table1

No. of Obs.

Fixed resistor value

Vout in the light Vout in the shade Voltage change

1 2 3 4 5

Voltage change= Vout in shade – Vout in light

document.doc 43

CIRCUIT DIAGRAM No. 1:

Fig.1 Circuit diagram

CONCLUSION:

1. With this circuit, is Vout HIGH or LOW in the light?

2. Which test resistor gives the biggest voltage change between light and shade?

3. Which resistor would you use to make your light sensor most sensitive to changes in illumination?

4. Repeat the procedure by changing the position of LDR and fixed resistor.

5. Now take Vout across the LDR

document.doc 44

CIRCUIT DIAGRAM 2:

Fig.2 Circuit diagram

Table 2

No. of Obs.

Fixed resistor value

Vout in the light Vout in the shade Voltage change

1 2 3 4 5

CONCLUSION:

1. With the second circuit, is Vout HIGH or LOW in the light?

2. Which test resistor gives the biggest voltage change between light and shade?

3. Which resistor would you use to make your light sensor most sensitive to changes in illumination?

document.doc 45

Experiment No. 10

CAREY FOSTER’S BRIDGE

OBJECTIVE:

To determine the value of an unknown small resistance using a Carey Foster’s bridge

EQUIPMENT:

An unknown resistance A known resistance(variable) A DMM A dry cell A plug key A meter bridge with jockey A sorting plate A copper strip

THEORY:The Carey Foster bridge is an electrical circuit that can be used to measure very small resistances. It works on the same principle as Wheatstone’s bridge, which consists of four resistances, P, Q, R and S that are connected to each other as shown in the circuit diagram below. In this circuit, G is a galvanometer, E is a lead accumulator, and K1 and K are the galvanometer key and the battery key respectively. If the values of the resistances are adjusted so that no current flows through the galvanometer, then if any three of the resistances P, Q, R and S are known, the fourth unknown resistance can be determined by using the relationship

P/ Q= R/S

Fig.1 Wheatstone’s bridge

document.doc 46

PROCEDURE:

The connections are made as shown in fig.2 such that potential divider acts as two equal resistances P & Q. Now connect the copper strip in right gap of the bridge and a known resistances (R) in the left gap. The null point is determined and it’s distance l′1 from the bridge is measured. Interchange the position of R and copper strip and note the distance l′2 of the new null point from the left end. Take at least three readings for different values of known resistances.

Now the given wire whose resistance is to be determined (say Y) is placed in the right gap in place of copper strip and known resistance in left gap (X).Find the null point and the distance l 1

and similarly l2 when X & Y are interchanged. Take at least three readings for different values of Y.

Fig.2 Block diagram Wheatstone’s bridge

FORMULAS USED

For unknown resistance Y:

Y=X-ρ(l2-l1)Ω

Where X is the resistance introduced in the resistance box

l1 is the length of the balance point in the bridge wire where resistance box is in the left gap

l2 is the length of the balance point in the bridge wire where resistance box is in the right gap

The resistance per unit length ( )of the bridge wire is determined by:ρ ρ= R/( l′2-l′1) ohm/cmWhere R is the known resistance in the resistance box.

document.doc 47

CALCULATIONS:Table 1For determination of ρ

Sr. No. R

Distance of the null pointShift in balance point ρ= R/( l′2-l′1)

When X in left gap When X in left gap l′2-l′1    ohm l′1 (cm) l′2(cm) cm ohm/cm

1          2          3          4          5          

Table 2 For determination of X

Sr. No. X

Distance of the null pointShift in balance point Y=X- ( l2-l1)

When Y in left gap When Yin left gap l2-l1    ohm l1 (cm) l2(cm) cm ohm/cm

1          2          3          4          5          

CONCLUSION:

1) What is the principle of Wheatstone bridge?

-------------------------------------------------------------------------------------------------------

-------------------------------------------------------------------------------------------------------

-------------------------------------------------------------------------------------------------------

2) What is the principle of Carey Foster’s bridge bridge?

-------------------------------------------------------------------------------------------------------

-------------------------------------------------------------------------------------------------------

-------------------------------------------------------------------------------------------------------

document.doc 48

3) When is the C.F. bridge most sensitive?

-------------------------------------------------------------------------------------------------------

-------------------------------------------------------------------------------------------------------

-------------------------------------------------------------------------------------------------------

Experiment No. 11

document.doc 49

SEXTANT

OBJECTIVE

To determine the height of inaccessible object.

EQUIPMENT:

Sextant

Rigid stand with clamp

Measuring tape

Plump line spirit level

Colored chalks

THEORY

A sextant is an instrument used to indirectly measure distances. A measuring tape or

meter stick is incapable of measuring the distance to a star. Sextants have been used for

centuries to make this sort of indirect measurement. In this activity sextants will be made

and used to measure the height of a very tall object, such as a flagpole or a building.

Fig.1 Sextant

document.doc 50

PROCEDURE1. Choose an observation point from which you can clearly see both the top and the bottom

of the object you wish to measure. Determine the exact distance between the observation point and the base of the object.

2. Set the sextant to zero and look at the object through the eyepiece, adjusting your view until it is in the center of the frame.

3. Adjust the sextant arm to split the screen in two halves. Continue moving the arm until the top half of the object on one side of the image is aligned with the bottom half of the object on the other side of the image.

4. Use a scientific calculator to find the height of the object by multiplying its distance from the observation point by the tan of the angle that you measured. For example, if you were 150 feet from the base of the object, and the recorded angle was 75 degrees, the height of the object would be 150 x tan 75 = 560 feet.

OBSERVATIONS & CALCULATIONS Vernier constant of the sextant =………… Initial reading of the vernier against

SS for the two mirrors parallel =………… Zero correction =………….. Height of the mark Q above the

ground =……........

Table 1

Sr. No.

Sextant at point R Sextant at point S

Horizontal distance

between the points R & S

(d)

Vertical distance

between the top and

reference mark Q

h=d/(cotθ2 -cotθ1)

Initial reading

A

Final reading

BAngle

θ1=B-A

Initial reading

C

Final reading

DAngle

θ2=D-C1                2                3                

document.doc 51

DISCUSSION AND CONCLUSION1) -------------------------------------------------------------------------------------------

2) -------------------------------------------------------------------------------------------

3) --------------------------------------------------------------------------------------------

document.doc 52

(SEMESTER PROJECT)

ELECTRIC MOTOR

OBJECTIVE: The objective of this project is to build a simple electric motor in order to explore the

inter-relationship of electricity & magnetism.

THEORY:

An electric motor is an electromechanical device that converts electrical energy into mechanical energy.

Most electric motors operate through the interaction of magnetic fields and current-carrying conductors to generate force. The reverse process, producing electrical energy from mechanical energy, is done by generators such as an alternator or a dynamo; some electric motors can also be used as generators, for example, a traction motor on a vehicle may perform both tasks. Electric motors and generators are commonly referred to as electric machines.

USES:

Electric motors are found in applications as diverse as industrial fans, blowers and pumps, machine tools, household appliances, power tools, and disk drives.

OPERATING PRINCIPLE:

Nearly all electric motors are based around magnetism (exceptions include piezoelectric motors and ultrasonic motors). In these motors, magnetic fields are formed in both the rotor and the stator. The product between these two fields gives rise to a force, and thus a torque on the motor shaft. One, or both, of these fields must be made to change with the rotation of the motor. This is done by switching the poles on and off at the right time, or varying the strength of the pole.

document.doc 53