Seebeck-Effect-Thermoelectricity

 Q. Define thermoelectricity?

Thermoelectricity:

It is the phenomenon in which heat energy is directly converted into electrical energy when two different metals are joined and their junctions are kept at different temperatures.

Q. What is thermocouple?

Thermocouple:

A thermocouple is a device made of two dissimilar metals joined at two junctions (one hot and one cold ) which produces an emf due to the temperature difference.

Q. What is Seebeck effect?

Seebeck Effect:

The Seebeck effect is the production of an emf in a closed circuit made of two different metals when their junctions are maintained at different temperatures.

Or

The Seebeck effect is the phenomenon in which an emf (voltage) is produced when two dissimilar metals form a closed circuit and their junctions are kept at different temperatures.

The size of the emf depends on the metals used and the temperature difference between the two junctions.

For curious minds

The Spark of Heat: The Story of Thermoelectricity

 A long time ago, in the year 1821, there lived a curious scientist named Thomas Seebeck. He loved to play with magnets, wires, and bits of metal. One chilly morning, while warming his hands by the fire, he had a bright idea!

“What happens,” he wondered, “if I join two different metals together and heat one end while keeping the other cool?”

He quickly twisted two wires (one of iron and one of copper) and made tiny loops at both ends. Then he held one end near the fire (the hot junction) and left the other end on his cold table (the cold junction).

To his surprise, something amazing happened : a magnetic needle nearby started to move!

Thomas was shocked . He realized that the heat had created electricity in the wires. The difference in temperature between the two ends made tiny electric charges start to move just like in a battery!

And that’s how thermoelectricity was discovered the idea that heat can make electricity.

Today, this same principle is used in thermocouples to measure temperature and even in space probes to make electricity from the Sun’s heat!

So, thanks to Thomas Seebeck’s curious mind, we now know that even a little bit of heat can make a powerful spark of science! 

The-Galvanometer-Structure-Working-Applications

 

The Galvanometer: Structure, Working, and Applications

 

Galvanometer is a sensitive instrument that detects and measures small electric currents.

 

What is a Galvanometer?

A galvanometer is an electromechanical device that converts electrical energy into mechanical movement.

When current flows through its coil, the instrument’s pointer deflects, giving a visual indication of the current’s presence and magnitude.

It works on the principle of electromagnetic deflection

Structure of a Moving Coil Galvanometer

The most common type used in laboratories is the Moving Coil Galvanometer. Its main parts are:

1. Moving Coil

•             A lightweight coil of copper wire, wound in a rectangular or circular shape.

•             Suspended between the poles of a permanent magnet.

•             Carries the current to be measured.

2. Permanent Magnet

•             Usually a horseshoe-shaped magnet producing a strong, radial magnetic field.

•             Ensures uniform torque on the coil for accurate readings.

3. Soft Iron Core

•             Placed inside the coil to strengthen the magnetic field and improve sensitivity.

4. Suspension System

•             A fine strip or wire (often gold or copper) suspends the coil and also conducts current into it.

•             Allows the coil to rotate freely.

5. Torsion Spring / Control Head

•             Provides a restoring torque to bring the pointer back to zero when no current flows.

•             Helps calibrate the instrument.

6. Pointer and Scale

•             The pointer is attached to the coil and moves over a calibrated scale.

•             Indicates the magnitude of current based on the coil’s deflection.

7. Mirror (in sensitive models)

•             Reflects a light beam for precise measurement of very small deflections.

Working Principle

When current flows through the coil:

1.          The coil generates its own magnetic field.

2.          This field interacts with the permanent magnet’s field.

3.          A torque is produced, causing the coil (and pointer) to rotate.

4.          The deflection angle is proportional to the current:

  5.          The torsion spring provides a restoring force, balancing the torque at a steady position.

 

Applications of a Galvanometer

•             Detecting Current: To check if current is flowing in a circuit.

•             Measuring Small Currents: Especially in physics experiments and sensitive circuits.

•             Analog Meters: Forms the core of devices like VU meters, light meters, and other sensor-based instruments.

•             Conversion to Ammeter: By connecting a low resistance (shunt) in parallel.

•             Conversion to Voltmeter: By connecting a high resistance in series.

•             Bridge Circuits: Used in Wheatstone bridge and other setups to detect balance points.

metre-bridge-current electricity

 

Metre Bridge

Above figure shows the diagram of meter bridge. It consists of a ---------

one-meter wire of uniform cross section fixed on a wooden table with a metre scale.

Two L shaped metallic strips separated by a single metallic strip,

an unknown resistance X connected in left gap and

a resistance box connected in right gap,

galvanometer connected to the central tap and other terminal is connected to the jockey J.

A cell of emf ε along with a key and a rheostat are connected between the points A and B.

Working:

A suitable resistance R is selected from resistance box. The jockey is brought in contact with AB at various points on the wire AB and the balance point (null point), D, is obtained. The galvanometer shows no deflection when the jockey is at the balance point.

If l_x and l_R are the respective lengths of the wire between AD and DC respectively, then using the conditions for balance we get

where R_AD and R_DB are resistance of the wire of the parts AD and DB.

The resistance R_AD and R_DB are given as

Thus if we know the value of R, l_x and l_R then we can determine the value of unknown resistance.

Two-Marks-Current electricity

 

Two Marks Each

1.  State the following laws

            I.        Kirchhoff’s Current Law

         II.        Kirchhoff’s Voltage Law

       III.        Potentiometer principle

2.  Define the following terms

a.  Potentiometer

b.  Potential gradient

3.  What are the advantages of potentiometer over voltmeter?

4.  Distinguish between voltmeter and ammeter

5.  What purpose the galvanometer is used for?

6.  Draw the internal structure of galvanometer.

7.  Write the balancing condition of Wheatstone bridge.

8.  Write any three conditions to convert a moving coil galvanometer into ammeter.

9.  Write any three conditions to convert a moving coil galvanometer into voltmeter.

10.     What are the uses of shunt?

11.     Write any three applications of potentiometer.

12.     What is sum method of potentiometer to compare the emfs of cell?

13.     What is the difference method of potentiometer to compare the emfs of cell?

14.     Draw the circuit diagram of Wheatstone bridge.

Full-Wave-Rectifier

 

Full Wave Rectifier

Figure 1 shows typical circuit of a full wave rectifier. The circuit consists of a center tapped transformer and diodes D₁ and D₂.

During the positive half cycle of the input voltage, the point A is at a higher potential than that of the point B and the diode D₁ conducts. The current through the load resistance R_L follows the path APQRC as shown in Fig.

During the negative half cycle of the input voltage, point B is at higher potential than point A and the diode D₂ conducts. The current through the load resistance R_L follows the path BPQRC.

Thus, the current flowing through the load resistance is in the same direction during both the cycles.

The input and output waveforms of a full wave rectifier are shown in Fig.2.

 

Half-Wave-Rectifier

 

Half Wave Rectifier

Above figure 1 shows the circuit diagram of half wave rectifier. As shown in the figure it consists of a transformer, the diode D and load resistance R_L.

The secondary coil AB of a transformer is connected in series with a diode D and the load resistance R_L.

When the positive half cycle begins, the voltage at the point A is at higher potential with respect to that at the point B, therefore, the diode (D) is forward biased. It conducts and current flows through the circuit.

When the negative half cycle begins, the voltage at the point A is lower potential with respect to the point B and the diode is reverse biased, therefore, it does not conduct. Current does not flow through the circuit.

Hence, the diode conducts only in the positive half cycles of the AC input.

The waveform for input and output voltages are shown in fig 2.

Hence a DC output voltage obtained across R_L is in the form of alternate pulses.

 .

Logic-Gates-Question-Bank

 

Logic Gates Practice Questions

Q.1. Draw the symbols and truth table for the following logic gates

1. NOT gate

2. OR gate

3. AND gate

4. NAND gate

5. NOR gate

6. EX-OR gate

Q.2. Which gate is called inverter?

Q.3. Why  is the NOT gate called inverter?

Q.4. Which gate is used to compare the level of input signals?

Q.5. Which gate gives the HIGH at it's output when all inputs are LOW? 

Q.6. Which gate is used to perform logical addition?

Q.7. Write the Boolean expression for 

        1. NOR gate

        2. NOT Gate

        3. OR Gate

        4. NAND Gate

        5. AND Gate

        6. XOR Gate

Q.8. Which Gates are called universal gates? Why?

Q.9. Define logic gate.

Q.10. What is the difference between analog and digital signal?

Logic Gates

 

Logic gates

Introduction:

Logic gates are the basic building blocks of digital electronics. They are used in telecommunications, calculators, computers, robots, industrial control systems etc.

In digital signals only discrete values of voltages are possible. To obtain the discrete values of voltages a pulse waveform is used which shows only two values of voltages.

HIGH voltage is written as 1 i.e. ON condition and LOW voltage is written as 0 i.e. OFF condition.

The logic gates follow the logical relationship between the input and output voltages.

Analog signal and Digital signal:

Continuous time varying voltage Vs Only two levels of voltages (HIGH or LOW)

                           

In fig. 1 the voltage has all values range from (0 – 5 volt). Thus as time changes, the voltage change from 0 – 5 volt or 5 – 0 volt.

In fig.2 the voltage has only two values 5 volt and 0 volt.

The HIGH/ON = 5 V

The LOW/OFF = 0 V

A digital circuit with one or more inputs but only one output signal is called a logic gate.

Logic gate is a switching circuit. It controls the flow of signal or information.

There are five common logic gates NOT Gate, AND Gate and OR Gate, NOR Gate, NAND Gate.

NOT Gate:

This is most basic gate with one input and one output. It produces 1 or HIGH at its output if the input is 0 or LOW and vice versa.

As NOT Gate produces the inversion of input at its output it is called INVERTER.

                        

                            

Above fig. shows the symbol and truth table of NOT Gate.

According to the truth table the timing diagram of NOT Gate can be drawn as

                    

                    

 OR Gate:

OR Gate performs logical addition or logical disjunction. The output of an OR gate is 1 when any one of its inputs is 1 or HIGH. The output of the OR gate is 0 only when all of its inputs are 0 or LOW.

                

Above fig. shows the symbol and truth table of OR Gate.

According to the truth table the timing diagram of OR Gate can be drawn as

                    

AND Gate:

AND Gate performs logical multiplication or logical conjunction. The output of an AND gate is 1 only when all of its inputs are 1 or HIGH. The output of the AND gate is 0 when any one of its inputs are 0 or LOW.

                                             

Above fig. shows the symbol and truth table of AND Gate.

According to the truth table the timing diagram of AND Gate can be drawn as

                        

NAND Gate:

This is AND Gate followed by NOT Gate.

The output of an NAND gate is 1 when any one of its inputs are 0 or LOW. The output of an NAND gate is 0 when all of its inputs are 1 or HIGH.

Therefore, it is called NOT AND Gate (behaviour).

NAND Gate is also called universal gate because by using the combinations of NAND Gate, other basic Gates can be obtained.

                                          

Above fig. shows the symbol and truth table of NAND Gate. According to the truth table the timing diagram of NAND Gate can be drawn as

                     

NOR Gate:

This is OR Gate followed by NOT Gate.

The output of an NOR gate is 1 only when both the inputs are low or 0. The output of NOR gate is 0 when any one of its inputs are 1 or HIGH.

Therefore, it is called NOT OR Gate (behaviour).

NOR Gate is also called universal gate because by using the combinations of NOR Gate, other basic Gates can be obtained.

                                        

Above fig. shows the symbol and truth table of NOR Gate. According to the truth table the timing diagram of NOR Gate can be drawn as

                     

Exclusive OR Gate/X-OR Gate:

Exclusive-OR gate can compare two logic levels and produce an output value dependent upon the input condition. The output of an Exclusive-OR gate goes 'HIGH' only when its two input terminals are at different logic levels with respect to each other.

An odd number of high or '1' at its input gives high or '1' at the output.

           

Above fig. shows the symbol and truth table of XOR Gate. According to the truth table the timing diagram of XOR Gate can be drawn as